Phenotypic Spectrum and Long-term Outcome in Children With Genetic Causes of Early-onset Epileptic Encephalopathy

DOI: https://doi.org/10.21203/rs.3.rs-257334/v1

Abstract

Background To explore the clinical phenotype and long-term outcome in children with genetic causes of early-onset epileptic encephalopathies.

Methods The clinical data of 118 children between 2010 and 2020 was obtained and analyzed. The whole exome sequencing and copy number variation studies in family were used to find pathogenic mutations. The confirmed mutations were verified by Sanger sequencing.

Results Among 118 patients, 39 patients were diagnosed with DS, 18 were WS, 3 were OS, 3 were EME, 2 were MMFSI, 1 was GLUT1 deficiency syndrome, 1 was Pyridoxine dependent epilepsy and 51 were non-symptomatic EOEEs. The initial EEG showed frequent multiple and multifocal sharp waves, spike waves, sharp slow waves or spike slow waves. In the later period, some transformed into infrequent discharging or normal EEG. 112 patients (112/118, 94.9%) showed normal brain MRI, and the remaining 6 had widened extracerebral space. In the later stage, 115 patients were re-examined with brain MRI 1 to 3 times, the widened gap became normal, only 2 had mild brain atrophy. After treatment, 42 patients (42/118, 35.6%) had seizure control. In EOEE-BS, 6 patients were found KCNQ2 mutations and the remaining mutations were SCN2A (n=2), STXBP1 (n=1). After treatment, only 2 patients had seizure control, 6 had uncontrolled seizures and 1 died. 7 patients with dyskinesia were found. 1 patient starting with a febrile convulsion was caused by HNRNPU mutation. SCN1A mutations were detected in 38 patients (38/118, 32.2%), representing the largest proportion. The second common mutations were KCNQ2 mutations in 9 patients. The third one was CDKL5 mutations in 8 patients. Genes associated with ionic channels represented the largest proportion (66/118, 55.9%), sodium channel potassium channel and calcium channel respectively. In WS, we detected SCN3A, SCN2A, SCN8A, CACNA1H, DEPDC5, MECP2, DYNC1H1, CDKL5, ALG11, CCDC88C, GABAA1, IL1RAPL1, RNASEH2B, SLC19A3, STXBP1, QARS, COL4A2 mutations. In addition to common gene mutations, we reported rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B and COL4A2 in WS. In non-syndromic genetic causes of EOEEs, we detected rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A. As for genetic modes, denovo heterozygous mutations account for the largest proportion (104/118, 88.1%). 3 patients with SMC1A mutations response to KD add-on therapy. VPA added treatment showed good effects on KCNB1 and PACS2 encephalopathy. LEV showed good effects on STXBP1, and OXC showed good effects on SCN8A encephalopathy.  

Conclusion The clinical manifestations of EOEE are variable, including dyskinesia. EOEE-BS usually response poorly to AEDS therapy. Although some patients achieve seizure-free, there is no remarkable improvement in their development. EOEEs starting with a febrile convulsion may be a special phenotype of HNRNPU related neurodevelopmental syndrome, similar to DS. We report rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B, COL4A2 in WS and detect rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A in non-syndromic genetic causes of EOEEs. Although genetic causes of EOEEs response poorly to AEDS treatment, we find that some gene mutation related EOEEs receive good effects on specific AEDS.

1. Introduction

Epilepsy is a disease of brain defined by at least two unprovoked (or reflex) seizures occurring > 24 h apart or one unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk (at least 60%) after two unprovoked seizures, occurring over the next 10 years, or diagnosis of an epilepsy syndrome[1]. A certain cluster of epilepsy syndromes is grouped as “early-onset epileptic encephalopathies” including early myoclonic encephalopathy(EME), Ohtahara syndrome(OS), West syndrome(WS), Dravet syndrome(DS), malignant migrating focal seizures of infancy (MMFSI) and non-syndromic epileptic encephalopathy[2]. Early-onset epileptic encephalopathies (EOEEs) or early infantile epileptic encephalopathies (EIEEs) are one of the most devastating early onset epilepsies that contributes to a progressive decline of cerebral function. The onset age of seizure is within 6 months. Most patients with EOEEs show three main features: refractory seizures, severe electroencephalography (EEG) abnormalities, and developmental delay or intellectual disability[3]. The etiology of EOEEs are classified as infectious, immune, structural, metabolic, genetic and unknown factors. Genetic etiology has attracted more attention with lots of gene mutations having been identified. At least 20–30% of EOEEs are caused by a single gene variation[4]. In recent years, an increasing number of novel genes are being identified in EOEEs. Many genes related to EOEEs have been detected, such as SCNIA, SCN2A, SCN8A, STXBP1, CDKL5 and KCNQ2[5]. Many patients with genetic causes of EOEEs are sporadic, occurring in patients with no family history of seizures or epilepsy. Although genetic causes of EOEEs are increasingly being identified, there is considerable genetic heterogeneity as well as phenotypic heterogeneity. A relatively rare clinical symptom, dyskinesia, has been identified in EOEEs[6]. And some specific phenotype, genetic causes of EOEE with burst suppression (EOEE-BS), has also been characterized[7, 8]. However, the long-term outcome of genetic causes of EOEEs remains unknown. Hence, there is a need to develop a deeper understanding of the broader clinical spectrum, specific genotype–phenotype and long-term outcome of genetic causes of EOEEs. In this study we aimed to describe the clinical features and long-term outcome of genetic causes of EOEEs in a cohort of patients and followed for a period of up to ten years.

2. Materials And Methods

2.1. Patients

The retrospective study included children with genetic causes of EOEEs at the Department of Neurology, Children’s Hospital of Fudan University.

The project ethics were approved by Ethic Committees of Children’s Hospital of Fudan University.
All the experiment protocol for involving humans was in accordance to guidelines of national/international/institutional or Declaration of Helsinki. Informed consent was obtained from all subjects.

The inclusion criteria are as follows: (1) seizure within 6 months after birth, (2) frequent seizures, (3) developmental retardation, stagnation or regression.

The exclusion criteria are as follows: (1) perinatal brain injury, (2) metabolic disease, (3) intrauterine infection, (4) neonatal and infantile seizures caused by brain structural abnormalities. The clinical data of 470 affected patients between January 2010 and January 2020 was obtained.

2.2. Next generation sequencing and copy number variation studies

The peripheral blood samples of these children and their parents were collected. The whole exome sequencing and copy number variation studies in family were used to find pathogenic mutations.

The inclusion criteria of sequencing are as follows: (1) insertion or deletion mutations, (2) mutations in coding amino acids or termination codons, (3) mutations in splicing sites, (4) non-synonymous mutations may destroy protein function predicted by PolyPhen-2 HVAR.

The exclusion criteria of sequencing are as follows: (1) copy number variations, microdeletions or microduplications, (2) nucleotide variations in all normal controls, (3) synonymous mutations, (4) single nucleotide polymorphisms (SNPs) annotated in human gene mutation database (HGMD), thousand human genome database, PubMed database and UCSC database.

Sanger sequencing was performed on verifying mutations. PolyPhen-2 analysis was carried out to predict variant effects. All patients were followed up for 1 year to 10 years.

3. Results

3.1 Patients’ demographics and clinical features

118 patients diagnosed with genetic causes of EOEEs were analyzed excluding 10 patients with copy number variations. The gene mutation rate was 27.2% (128/470). Among 118 patients, 62 (62/118, 52.5%) were males, 56 (56/118,47.5%) were females. The seizure onset age ranged from 1 day to 6 months (3.5 ± 1.5 months). Their parents were not close relatives, and these children were not related except patients 73 and 74.

39 patients (39/118, 33.1%) were diagnosed with DS, 18 (18/118, 15.3%) were WS, 3 (3/118, 2.5%) were OS, 3 (3/118, 2.5%) were EME, 2 (2/118,1.7%) were MMFSI, 1 (3/52, 0.8%) was GLUT1 deficiency syndrome, 1 (1/118, 0.8%) was Pyridoxine dependent epilepsy, 51 (51/118, 43.3%) were non-symptomatic EOEEs. The initial EEG showed frequent multiple and multifocal sharp waves, spike waves, sharp slow waves or spike slow waves. In the later period, some transformed into infrequent discharging or normal EEG. 112 patients (112/118, 94.9%) showed normal brain MRI, and the remaining 6 had widened extracerebral space. In the later stage, 115 patients were re-examined with brain MRI 1 to 3 times, the widened gap became normal, only 2 had mild brain atrophy. After treatment, 42 patients (42/118, 35.6%) had seizure control. 16 patients (16/118, 13.6%) had seizure control for more than 1 year, 3 (3/118, 2.5%) had seizure control for more than 2 years, 9 patients had seizure control for more than 3 years (9/118, 7.6%), 8 had seizure control for more than 4 years (8/118, 6.8%), 4 had seizure control for more than 5 years (4/118, 3.4%), 2 had seizure control for more than 6 years (2/118, 1.7%). 2 patients died from SE (2/118, 1.7%). At the final follow-up, those patients remained seizure-free but no remarkable improvement in their development. 38 patients diagnosed with DS caused by SCN1A are not listed in Table 1 because their clinical features are easily identified. All remaining 80 patients’ features were summarized in Table 1.

Table 1

Summary of the phenotypic features in our 80 patients

P

Gene

Current age,

Sex

Seizure

onset age

Seizure

semiology

Other

Phenotype

Development retardation

Epilepsy

syndrome

EEG

MRI

AEDS tried

Effective

AEDS

Seizure

outcome

1

SCN2A

10y, F

3d

FS, GTCS,

T

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

B6

TPM

LEV

VPA

LTG

OXC

PB

KD

No

Uncontrolled

2

SCN2A

10y, F

5m

FS, GTCS,

T, SE

No

Severe

Severe

EOEE

BS

Frequent

Infrequent

N

Atrophy

TPM

VPA

LTG

OXC

LEV

PB

Mexitil

KD

VNS

No

Uncontrolled

3

SCN2A

5y, M

4m

S

No

Severe

Moderate

WS

BS

H

Infrequent

N

N

VPA

MP

KD

MP

KD

Controlled

Free for 3y

4

SCN3A

8y, M

6m

S

No

Severe

Moderate

WS

H

Infrequent

N

N

VPA

P

KD

P

KD

Controlled

Free for 4y

5

SCN8A

10y, M

6m

S

No

Severe

Moderate

WS

H

Infrequent

N

N

ACTH

P

TPM

ACTH

P

TPM

Controlled

Free for 5y

6

SCN8A

3y, M

6m

FS, T, S

No

Severe

Severe

EOEE

Frequent

Infrequent

WG

N

LEV

CZP

TPM

OXC

OXC

Controlled

Free for 2y

7

SCN8A

3y, F

6m

T, FS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

LEV

PB

VPA

TPM

OXC

KD

No

Uncontrolled

8

SCN8A

5y, F

6m

S, FS,

T, AA

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

ACTH

P

OXC

TPM

LCM

KD

No

Uncontrolled

9

SCN8A

2y, M

6m

FS

No

Severe

Severe

EOEE

Infrequent

Infrequent

N

N

PB

OXC

OXC

Controlled

Free for 1y

10

KCNQ2

6m, M

6d

GTCS, SE

No

Severe

EOEE

Frequent,

Low voltage,

BS

N

B6

PB

VPA

LEV

No

Died of SE

at 6m

11

KCNQ2

4y, M

1d

T, FS, S

No

Severe

Severe

OS

Frequent,

BS

Infrequent

N

N

B6

LEV

OXC

TPM

No

Uncontrolled

12

KCNQ2

4y, F

1d

FS,T

No

Severe

Severe

EOEE

BS

Frequent

Frequent

N

N

B6

TPM

OXC

VPA

LCM

KD

No

Uncontrolled

13

KCNQ2

6y, M

3m

T, GTCS

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

TPM

OXC

LEV

VPA

LTG

KD

No

Uncontrolled

14

KCNQ2

7y, M

3d

FS,S, GTCS

No

Severe

Severe

EOEE

BS

Frequent

Frequent

N

N

B6

NZP

LEV

ACTH

P

OXC

TPM

KD

TPM

KD

Controlled

Free for 4y

15

KCNQ2

5y, M

1d

FS,T, GTCS

No

Severe

Severe

EOEE

BS

Frequent

Frequent

N

N

B6

PB

LEV

OXC

TPM

VPA

KD

No

Uncontrolled

16

KCNQ2

2y, M

10d

FS,T, GTCS

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

B6

PB

LEV

TPM

PB

LEV

TPM

Controlled

Free for 1y

17

KCNQ2

2y, M

3d

FS,T, S,GTCS

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

B6

PB

LEV

ACTH

TPM

VPA

No

Uncontrolled

18

KCNQ2

2y, M

4d

FS,T, S,GTCS

No

Severe

Severe

OS

WS

BS

Frequent

H

Frequent

N

N

B6

PB

LEV

ACTH

P

TPM

VPA

OXC

KD

No

Uncontrolled

19

KCNQ3

2y, M

6m

S,FS,T,

GTCS, M

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

VPA

LEV

TPM

ACTH

P

VGB

OXC

No

Uncontrolled

20

KCTD7

10y, M

5m

M,FS,T

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

N

LEV

VPA

TPM

VPA

TPM

Controlled

Free for 4y

21

KCNB1

10y, F

6m

FS,T

No

Severe

Severe

EOEE

Frequent

ESES

Infrequent

N

N

P

VPA

P

VPA

Controlled

Free for 5y

22

KCNB1

4y, M

6m

FS,T

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

LEV

VPA

LEV

VPA

Controlled

Free for 3y

23

KCNT1

4y, F

1.5m

FS,T

No

Severe

Severe

MMFSI

Migrating

Frequent

Frequent

N

N

PB

LEV

VPA

OXC

TPM

QD

KD

No

Uncontrolled

24

KCNT1

2y, M

3d

FS,T

No

Severe

Severe

MMFSI

Migrating

Frequent

Frequent

N

N

B6

OXC

LEV

CZP

VPA

TPM

QD

CLB

KD

No

Uncontrolled

25

HCN1

8y, M

6m

FS,T

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

OXC

NZP

VPA

VPA

Controlled

Free for 4y

26

CACNB4

6y, F

1m

FS,T

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

B6

PB

OXC

OXC

Controlled

Free for 3y

27

CACNA1H

6y, M

6m

S

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

MP

VPA

TPM

OXC

LTG

KD

No

Uncontrolled

28

CACNA1E

2y, M

20d

FS,T,

GTCS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

OXC

LEV

VPA

TPM

VPA

TPM

Controlled

Free for 1y

29

CDKL5

8y, F

3m

FS,T,

GTCS, S

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

KD

No

Uncontrolled

30

CDKL5

8y, F

2m

FS,T,S

GTCS

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

KD

No

Uncontrolled

31

CDKL5

8y, F

2m

FS,T,S

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

KD

No

Uncontrolled

32

CDKL5

6y, F

1m

FS,T,S

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

KD

No

Uncontrolled

33

CDKL5

8y, F

2m

FS,T,

GTCS

Chorea

Severe

Severe

EOEE

Frequent

Infrequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

KD

No

Uncontrolled

34

CDKL5

5y, F

6m

S, M, FS

Chorea

Severe

Severe

EOEE

Frequent

Infrequent

WG

N

VPA

TPM

OXC

LEV

PB

LTG

KD

KD

Controlled

Free for 3y

35

CDKL5

4y, F

6m

GTCS,T, S, FS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

N

ACTH

P

VPA

TPM

OXC

LEV

PB

LTG

KD

KD

Controlled

Free for 3y

36

CDKL5

4y, F

1m

GTCS,T, S, FS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

ACTH

P

VPA

TPM

OXC

LEV

PB

LTG

KD

KD

Controlled

Free for 2y

37

PCDH19

10y, F

5m

FS,GTCS,

T

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

VPA

LEV

TPM

No

Uncontrolled

38

PCDH19

7y, F

5m

FS,T,

GTCS, M

No

Severe

Severe

DS

Infrequent

Infrequent

N

N

VPA

TPM

OXC

LEV

PB

LTG

LCM

KD

No

Uncontrolled

39

PCDH19

8y, F

6m

FS,T,

GTCS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

OXC

VPA

TPM

PB

LTG

KD

No

Uncontrolled

40

PCDH19

4y, F

5m

FS,T,

GTCS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

OXC

VPA

TPM

PB

LTG

LCM

KD

No

Uncontrolled

41

SLC2A1

8y, M

2d

FS,T,

GTCS

Dystonia

Severe

Severe

GLUT1

Frequent

Infrequent

N

WG

N

VPA

LEV

KD

BAL

KD

Controlled

Free for 6y

42

STXBP1

2y, M

1m

FS,T,

GTCS

Dystonia

Severe

Severe

EOEE

Frequent

Infrequent

Infrequent

N

N

PB

LEV

BAL

LEV

Controlled

Free for 1y

43

STXBP1

2y, M

2m

S, T, FS,

GTCS

Dystonia

Severe

Severe

WS

H

Frequent

Infrequent

WG

Arachnoid Cysts

Arachnoid Cysts

PB

ACTH

P

VGB

LEV

BAL

LEV

Controlled

Free for 1y

44

STXBP1

7y, M

1m

T, FS, S,

GTCS

No

Severe

Severe

OS

BS

Frequent

N

N

B6

PB

TPM

LEV

VPA

OXC

KD

No

Uncontrolled

45

SETBP1

9y, M

6m

T, FS,

GTCS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

N

PB

TPM

LEV

VPA

VPA

Controlled

Free for 5y

46

ARHGEF9

8y, M

4m

T, FS,

GTCS

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

LEV

OXC

OXC

Controlled

Free for 4y

47

GABRG2

8y, M

5m

T, FS,

GTCS

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

PB

LEV

VPA

LEV

VPA

Controlled

Free for 5y

48

GABAA1

3y, M

4m

S

No

Severe

Moderate

WS

H

Frequent

Infrequent

N

N

ACTH

P

KD

TPM

VGB

TPM

VGB

Controlled

Free for 1.5y

49

GABRA2

2y, M

6m

T, FS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

LEV

VPA

LEV

VPA

Controlled

Free for 1y

50

DEPDC5

5y, M

1m

S, FS

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

LEV

TPM

P

OXC

KD

VGB

No

Uncontrolled

51

MECP2

8y, F

2m

S, FS, T

No

Severe→

Severe

WS

H

Frequent

Infrequent

N

N

P

VPA

CZP

TPM

VPA

TPM

Controlled

Free for 3y

52

GRIN3B

10y, M

6m

FS,T, GTCS

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

PB

OXC

VPA

OXC

VPA

Controlled

Free for 6y

53

GRIA4

3y, M

6m

FS,T, GTCS

Ataxia

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

PB

OXC

VPA

TPM

VPA

TPM

Controlled

Free for 2y

54

DYNC1H1

5y, M

2m

S, FS,T,

No

Severe

Severe

WS

Frequent

Frequent

N

N

ACTH

P

VPA

CZP

TPM

No

Uncontrolled

55

ALDH7A1

5y, F

2d

FS,T, GTCS

No

Severe

Moderate

Pyridoxine dependent epilepsy

Frequent

Infrequent

N

N

N

LEV

PB

B6

B6

Controlled

Free for 4y

56

DPYD

5y, F

2m

FS,T, GTCS

No

Severe

Severe

EOEE

Frequent

Frequent

N

N

PB

LEV

TPM

OXC

VPA

LTG

KD

No

Uncontrolled

57

ALG11

2y, F

3m

S,FS,T

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

ACTH

P

LEV

TPM

OXC

VPA

LTG

KD

No

Uncontrolled

58

CCDC88C

2y, F

3m

S,FS,T

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

ACTH

P

LEV

TPM

OXC

VPA

LTG

KD

No

Uncontrolled

59

CSNK2B

2y, F

2m

FS,T,

GTCS

No

Severe

Moderate

EOEE

Frequent

Infrequent

WG

N

LEV

VPA

No

Controlled

Free for 1y

60

CSNK2B

3y, M

3m

FS,T,

GTCS

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

LEV

VPA

No

Controlled

Free for 1.5y

61

IL1RAPL1

3y, M

6m

S,FS,T

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

ACTH

P

TPM

KD

VGB

KD

Controlled

Free for 1.5y

62

IQSEC2

2y, M

6m

S,FS,T

No

Severe

Severe

WS

H

Frequent

Frequent

N

N

ACTH

P

TPM

KD

VGB

No

Uncontrolled

63

PACS2

5y, M

10d

FS,T

Special face

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

B6

LEV

VPA

VPA

Controlled

Free for 4y

64

PACS2

2y, F

1m

FS,T

Microcephaly

Special face

Severe

Severe

EOEE

Frequent

Infrequent

N

N

B6

LEV

TPM

BP

KD

VPA

VPA

Controlled

Free for 1y

65

PACS2

2y, F

1m

FS,T

Special face

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

B6

LEV

VPA

VPA

Controlled

Free for 1y

66

PIGA

6y, M

6m

FS,T, SE

No

Severe

Severe

EOEE

Frequent

Infrequent

N

Atrophy

LEV

PB

VPA

TPM

KD

KD

Controlled

Free for 3y

67

QARS

3y, F

2m

FS,T, S

No

Severe

Severe

WS

H

Frequent

N

N

LEV

ACTH

P

TPM

KD

No

Uncontrolled

68

RNASEH2B

3y, F

4m

FS,T, S

No

Severe

Severe

WS

H

Frequent

N

N

LEV

ACTH

P

TPM

VPA

KD

No

Uncontrolled

69

SMC1A

4y, F

6m

FS,

Cluster

Seizures

No

Severe

Severe

EOEE

Frequent

Infrequent

N

N

LEV

OXC

KD

KD

Controlled

Free for 3y

70

SMC1A

2y, F

2.5m

FS,

Cluster

seizures

No

Moderate

Moderate

EOEE

H

Frequent

N

LEV, TPM, PB

OXC

KD

Controlled

Free for 1y

71

SMC1A

1.5y, F

3m

FS,

Cluster

seizures

No

Moderate

Moderate

EOEE

Frequent

Infrequent

N

LEV

OXC

KD

KD

Controlled

Free for 1y

72

TBC1D24

15y, F

6m

M, FS,T,

EPC

Dystonia

Severe

Severe

EME

Frequent

Infrequent

N

N

LEV

PB

VPA

LTG

CLB

KD

No

Uncontrolled

73

TBC1D24

8y, F

3m

M, EPC

No

Severe

Severe

EME

Frequent

Infrequent

N

N

LEV

PB

VPA

LTG

CLB

OXC

NZP

No

Uncontrolled

74

TBC1D24

5y, M

3m

M, EPC

No

Severe

Severe

EME

Frequent

Infrequent

N

N

LEV

PB

VPA

LTG

CLB

OXC

NZP

No

Uncontrolled

75

WWOX

5y, M

6m

FS,T

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

PB

LEV

NZP

NZP

Controlled

Free for 3y

76

COL4A2

2y, M

3m

S

No

Severe

Severe

WS

H

Frequent

N

ACTH

P

ACTH

P

Controlled

Free for 1y

77

PTEN

5y, F

6m

S,FS

No

Severe

Severe

WS

H

Frequent

N

N

MP

TPM

VPA

KD

CLB

LTG

No

Uncontrolled

78

H3F3A

2y, M

2m

FS,T

No

Severe

Severe

EOEE

Frequent

Frequent

WG

BP

LEV

LEV

Controlled

Free for 1y

79

CHD2

11y, M

6m

FS,T,

GTCS, M

No

Severe

Moderate

EOEE

Frequent

Infrequent

N

N

N

BP

LEV

OXC

VPA

LTG

KD

No

Uncontrolled

80

HNRNPU

6y, M

6m

FS,T,

GTCS,AA

No

Moderate

Moderate

EOEE

Infrequent

Frequent

N

N

BP

LEV

VPA

VPA

Controlled

Free for 2y

3.2 EOEE-BS

In our study, children with EOEE-BS had various clinical phenotypes. The common phenotypes were OS and non-syndromic EOEE. 7 patients with early EEG persistent BS from 1 day to 1 month, 1 of which was accompanied by double hemisphere intermittent low voltage. The persistent BS disappeared at 2 to 3 months. For the other 2 patients caused by SCN2A mutations, EEG was temporary BS during sleep at 4 months and 5 months, and disappeared at 7 months. After performing genetic tests, 6 patients were found KCNQ2 mutations and the remaining mutations were SCN2A (n = 2), STXBP1 (n = 1). After treatment, only 2 patients had seizure control, 6 had uncontrolled seizures and 1 had died from SE at 6 months.

3.3 EOEEs with dyskinesia

A total of 7 children diagnosed with EOEES with dyskinesia were found. The dyskinesia onset age ranged from 1 month to 1 year. 2 patients with dyskinesia showed dancing-like movements, 4 patients showed dystonia, 1 patient showed ataxia. Genetic mutations included CDKL5(n = 2), SLC2A1 (n = 1), STXBP1 (n = 2), TBC1D24 (n = 1), GRIA4 (n = 1). Patients with CDKL5 encephalopathy with dyskinesia were given Madopar but they continued to have chorea. 4 patients with dystonia received good effect while on Baclofen. Among them, 1 patient with STXBP1 encephalopathy showed good responses while on LEV.

3.4 EOEEs limited to females with cluster seizures

Three patients with heterozygous de novo mutations in SMC1A gene were reviewed. All patients were females with moderate to severe developmental impairment. None of them had a clinical diagnosis of Cornelia de Lange syndrome. All three patients had prominent clinical features of cluster seizures. All the nonsense mutations were predicted damaging SMC1A protein by PolyPhen-2 HVAR. All the patients were treated with multiple antiepileptic drugs but their seizures remained refractory. When initiated with ketogenic diet, they became seizure free within 3 to 4 weeks.

3.5 EOEEs starting with a febrile convulsion

The typical clinical features of DS is that the onset of a febrile convulsion often within 1-year-old, which is characterized by repeated generalized or hemiclonic seizures. Except for DS, we found another type of EOEE starting with a febrile convulsion caused by HNRNPU mutation. The index patient was a 6 years boy, being a first-born child from full term pregnancy and natural birth. Both the pregnancy and delivery history of this boy were unremarkable. In his family history, there was no similar disease. Developmental milestone showed moderate developmental retardation. She began having a febrile convulsion at 6 months of age, which occurred 5 times a day. Video EEG showed slow activity in the background and sharp slow waves in the left occipital and posterior temporal regions during the interictal period. A febrile convulsion occurred once in half a year on average. At the age of 4 years, he began to suffer seizures without any inducing factors. EEG showed a large number of multifocal sharp waves, spike waves, and spike slow waves. The effect of BP and LEV was poor, and the epileptic seizure was reduced associated with VPA. At the final follow-up, she remained seizure-free for 2 years with LEV and VPA treatment but no remarkable improvement in his development.

3.6 Genetic analysis

38 Patients diagnosed with DS caused by SCN1A are not listed in Table 1 because their clinical features are easily identified. SCN1A mutations were detected in these 38 patients(38/118, 32.2%), representing the largest proportion, including 27 missense, 7 frameshift and 4 nonsense mutations. Our other findings suggested that genetic causes of EOEEs involve pathogenic mutations (54 missense,11 frameshift, 12 nonsense, 3 splicing mutations) (Fig. 1). All 80 patients’ genetic findings were summarized in Table 2. All 80 patients’ genetic findings were summarized in Table 2. We identified different specific types of EOEE. The identified genes were summarized in Table 3. SCN1A mutations were detected in 38 patients, representing the largest proportion (38/118, 32.2%). The second common mutations were KCNQ2 mutations, detected in 9 patients. The third one was CDKL5 mutations, identified in 8 patients. Genes associated with ionic channels represented the largest proportion(66/118, 55.9%), sodium channel potassium channel and calcium channel respectively. The number of identified genes were summarized in Table 4.

Table 2

Summary of the genetic findings in our 80 patients

P

Gene

Base change

Amino acid change

Predicted effect

on protein

Zygosity

Inheritance

1

SCN2A

c.5635A > G

p.M1879V

Missense

Heterozygous

De novo

2

SCN2A

c.4384delT

p.F1462Sfs

Frameshift

Heterozygous

De novo

3

SCN2A

c.1159G > A

p.E387K

Missense

Heterozygous

De novo

4

SCN3A

c.716C > A

p.A239A

Missense

Heterozygous

De novo

5

SCN8A

c.641G > A

p.G214D

Missense

Heterozygous

De novo

6

SCN8A

c.2942G > C

p.S981T

Missense

Heterozygous

De novo

7

SCN8A

c.2879T > A

p.V960A

Missense

Heterozygous

De novo

8

SCN8A

c.641G > A

p.G214D

Missense

Heterozygous

De novo

9

SCN8A

c.5498A > T

p.A1833V

Missense

Heterozygous

De novo

10

KCNQ2

c.14G > T

p.5S > X

Nonsense

Heterozygous

De novo

11

KCNQ2

c.629G > A

p.A210H

Missense

Heterozygous

De novo

12

KCNQ2

c.740C > T

p.S247L

Missense

Heterozygous

De novo

13

KCNQ2

c.821C > T

p.T274M

Missense

Heterozygous

De novo

14

KCNQ2

c.1678C > T

p.A560T

Missense

Heterozygous

De novo

15

KCNQ2

c.821C > T

p.T274M

Missense

Heterozygous

De novo

16

KCNQ2

c.649A > C

p.T217P

Missense

Heterozygous

De novo

17

KCNQ2

c.1179del

p.Leu394T

Frameshift

Heterozygous

De novo

18

KCNQ2

c.2048_2051dup

p.C685AfsT181

Frameshift

Heterozygous

De novo

19

KCNQ3

c.1231A > T

p.L411T

Nonsense

Heterozygous

De novo

20

KCTD7

c.334C > G

c.686A > T

p.A112G

p.A229V

Missense

Missense

Compound

heterozygous

Father

Mother

21

KCNB1

c.916C > T

p.A306C

Missense

Heterozygous

De novo

22

KCNB1

c.635C > A

p.P212H

Missense

Heterozygous

De novo

23

KCNT1

c.1421G > A

p.A474H

Missense

Heterozygous

De novo

24

KCNT1

c.1420C > T

p.A474C

Missense

Heterozygous

De novo

25

HCN1

c.1679G > A

p.R560H

Missense

Heterozygous

De novo

26

CACNB4

c.668C > T

p.T223M

Missense

Heterozygous

De novo

27

CACNA1H

c.2491G > A

p.V831M

Missense

Heterozygous

De novo

28

CACNA1E

c.2767C > T

p.H923T

Missense

Heterozygous

De novo

29

CDKL5

c.1326_1327ins A

p.443,N > Kfs

Frameshift

Heterozygous

De novo

30

CDKL5

c.1794_1795ins A

p.332,N > Kfs

Frameshift

Heterozygous

De novo

31

CDKL5

IVS9-1G > A

Splice

Splicing

Heterozygous

De novo

32

CDKL5

c.2774_c.2775: del TG

p.925M > lfs

Frameshift

Heterozygous

De novo

33

CDKL5

c.1245_c.1246: del AG

p.T415Tfs

Frameshift

Heterozygous

De novo

34

CDKL5

c.1700C > T

p.T567M

Missense

Heterozygous

De novo

35

CDKL5

c.238C > T

p.R80C

Missense

Heterozygous

De novo

36

CDKL5

c.428T > A

p.I143A

Missense

Heterozygous

De novo

37

PCDH19

c.471C > G

p.A157G

Missense

Heterozygous

De novo

38

PCDH19

c.2341delA

p.I781Sfs

Frameshift

Heterozygous

De novo

39

PCDH19

c.2113C > T

p.A705T

Nonsense

Heterozygous

De novo

40

PCDH19

c.798C > G

p.A266G

Missense

Heterozygous

De novo

41

SLC2A1

c.1278 + 30_1278 + 31insATTTCTCACC

Splice

Splicing

Homozygosis

De novo

42

STXBP1

c.69_c.70insA

p.L24Lfs

Frameshift

Heterozygous

De novo

43

STXBP1

c.364C༞T

p.A122T

Nonsense

Heterozygous

De novo

44

STXBP1

c.364C > T

p122R > X

Nonsense

Heterozygous

De novo

45

SETBP1

c.2339C > G

PS780T

Nonsense

Heterozygous

De novo

46

ARHGEF9

c.1364A > C

p.G455P

Missense

Heterozygous

De novo

47

GABRG2

c.929C > T

p.T310I

Missense

Heterozygous

De novo

48

GABAA1

c.779C > T

p.P260L

Missense

Heterozygous

De novo

49

GABRA2

c.995C > T

p.A332V

Missense

Heterozygous

De novo

50

DEPDC5

c.280-1G > A

Splicing

Splicing

Heterozygous

De novo

51

MECP2

c.158G > T

p.G53V

Missense

Heterozygous

De novo

52

GRIN3B

c.1829G > A

p.A610H

Missense

Heterozygous

De novo

53

GRIA4

c.1378A > G

p.I460V

Missense

Heterozygous

De novo

54

DYNC1H1

c.1682A > G

p.G561G

Missense

Heterozygous

De novo

55

ALDH7A1

c.961G > A

p.A321T

Missense

Homozygosis

De novo

56

DPYD

c.1774C > T

c.2897C > T

p.R592W

p.S966F

Missense

Missense

Compound

heterozygous

Father

Mother

57

ALG11

c.1192G > A

c.1403G > A

p.G398L

p.A468H

Missense

Missense

Compound

heterozygous

Mother

Father

58

CCDC88C

c.1158G༞C

c.5635C༞T

p.E386D

p.R1879W

Missense

Missense

Compound

heterozygous

Mother

Father

59

CSNK2B

c.508_509del

p.V170Afs

Frameshift

Heterozygous

De novo

60

CSNK2B

c.142C > T

p.G48T

Nonsense

Heterozygous

De novo

61

IL1RAPL1

c.2062G > C

p.G688G

Missense

Heterozygous

De novo

62

IQSEC2

c.2776C > T

p.A926T

Nonsense

Hemizygous

De novo

63

PACS2

c.625G > A

p.G209L

Missense

Heterozygous

De novo

64

PACS2

c.625G > A

p.G209L

Missense

Heterozygous

De novo

65

PACS2

c.625G > A

p.G209L

Missense

Heterozygous

De novo

66

PIGA

c.241C > T

p.A81C

Missense

Hemizygous

De novo

67

QARS

c.1852G > A

c.2068C > T

p.A618A

p.A690C

Missense

Missense

Compound

heterozygous

Mother

Father

68

RNASEH2B

c.629G > A

c.905G > A

p.A210H

p.G302G

Missense

Missense

Compound

heterozygous

Mother

Father

69

SMC1A

c.1495C > T

p.A499T

Nonsense

Heterozygous

De novo

70

SMC1A

c.1489C > T

p.G497T

Nonsense

Heterozygous

De novo

71

SMC1A

c.3463C > T

p.G1155T

Nonsense

Heterozygous

De novo

72

TBC1D24

c.1571G > C

c.680G > A

p.A524P

p.A227G

Missense

Missense

Compound

heterozygous

Mother

Father

73

TBC1D24

c.1207G > T

c.1499C > T

p.V403L

p.A500V

Missense

Missense

Compound

heterozygous

Father

Mother

74

TBC1D24

c.1207G > T

c.1499C > T

p.V403L

p.A500V

Missense

Missense

Compound

heterozygous

Father

Mother

75

WWOX

c.468G > T

p.A156S

Missense

Homozygosis

De novo

76

COL4A2

c.1148C > T

p.P383L

Missense

Heterozygous

De novo

77

PTEN

c.1034T > C

p.L345P

Missense

Heterozygous

De novo

78

H3F3A

c.377A > G

p.G126A

Missense

Heterozygous

De novo

79

CHD2

c.4909C > T

p.A1637T

Nonsense

Heterozygous

De novo

80

HNRNPU

c.1341dup

p.V448Cfs

Frameshift

Heterozygous

De novo

Table 3

Summary of the identified genes in specific EOEEs

Specific classifications of EOEE

Associated gene

Dravet syndrome

SCN1A

Ohtahara syndrome

KCNQ2, STXBP1

West syndrome

SCN3A, SCN2A, SCN8A, CACNA1H, DEPDC5, MECP2, DYNC1H1, CDKL5, ALG11, CCDC88C, GABAA1, IL1RAPL1, RNASEH2B, SLC19A3, STXBP1, QARS, COL4A2

Early myoclonic epileptic encephalopathy

TBC1D24

GLUT1 deficiency syndrome

SLC2A1

Malignant migrating focal seizures of infancy

KCNT1

EOEE-BS

KCNQ2、STXBP1、SCN2A、PIGA

EOEEs with dyskinesia

STXBP1, CDKL5, SLC2A1

EOEEs limited to females with cluster seizures

SMC1A

EOEEs starting with febrile convulsion

SCN1A,PCDH19༌HNRNPU

Table 4

Summary of the number of identified genes in EOEEs

Gene function

Mutated gene

Corresponding total cases

Sodium channel

SCN1A, SCN2A, SCN3A, SCN8A

38, 3, 1, 5

Potassium channel

KCNQ2, KCNQ3, KCTD7,KCNB1,

KCNT1,HCN1

9, 1, 1, 2, 2, 1

Calcium channel

CACNB4, CACNA1H, CACNA1E

1, 1, 1

Cyclin-dependent kinase-like

CDKL5

8

Protocadherin

PCDH19

4

Solute carrier family

SLC2A1

1

Syntaxin-binding protein

STXBP1

3

SET binding protein

SETBP1

1

CDC42 guanine nucleotide exchange factor

ARHGEF9

1

Gamma-aminobutyric acid receptor

GABRG2, GABAA1, GABRA2

1, 1, 1

DEP domain containing 5, GATOR1 subcomplex subunit

DEPDC5

1

Methyl-CpG binding protein

MECP2

1

Glutamate ionotropic receptor

GRIN3B, GRIA4

1, 1

Dynein cytoplasmic 1 heavy chain

DYNC1H1

1

Aldehyde dehydrogenase 7 family member

ALDH7A1

1

Dihydropyrimidine dehydrogenase

DPYD

1

ALG11 alpha-1,2-mannosyltransferase

ALG11

1

Coiled-coil domain containing

CCDC88C

1

Casein kinase 2

CSNK2B

2

Interleukin 1 receptor accessory protein like

IL1RAPL1

1

IQ motif and Sec7 domain ArfGEF

IQSEC2

1

Phosphofurin acidic cluster sorting protein

PACS2

3

Phosphatidylinositol glycan anchor biosynthesis class

PIGA

1

Glutaminyl-tRNA synthetase

QARS

1

Ribonuclease H2 subunit

RNASEH2B

1

Structural maintenance of chromosomes

SMC1A

3

TBC1 domain family member

TBC1D24

3

WW domain containing oxidoreductase

WWOX

1

Collagen type IV chain

COL4A2

1

Phosphatase and tensin homolog

PTEN

1

H3.3 histone

H3F3A

1

Chromodomain helicase DNA binding protein

CHD2

1

Heterogeneous nuclear ribonucleoprotein

HNRNPU

1

3.7 Genetic causes of EOEEs with a good therapeutic effect

In general, the effect of KD is sure on the treatment of genetic causes of EOEEs. 3 patients with SMC1A mutations response to KD add-on therapy. VPA added treatment showed a good effect on KCNB1 (n = 2) and PACS2 (n = 3) encephalopathy. LEV added treatment showed a good effect on STXBP1 (n = 2)encephalopathy. OXC added treatment showed a good effect on SCN8A (n = 2)encephalopathy.

4. Discussion

We report a series of individuals with genetic causes of EOEEs, delineating the phenotypic spectrum and long-term outcome. In the unknown causes of EOEEs, detection of the gene mutation rate was 27.2% (128/470). In the genetic causes of EOEEs, the non-symptomatic EOEEs represent the largest proportion, which is 43.3% (51/118). We find the initial EEG of most patients showing frequent multiple and multifocal discharging. With seizure controlled, EEG discharging gradually decreases. But only a minority of patients’ EEG transform into infrequent discharging or normal EEG. Despite performing several brain MRI, there is no significant change in the later brain MRI. In the long outcome, we find the seizure control rate in the genetic causes of EOEEs is 35.6% (42/118). The death rate is 1.7% (2/118). And we don’t find sudden unexpected death in the genetic causes of EOEEs. Although some patients achieve seizure-free, there is no remarkable improvement in their development.

BS is a common EEG phenomenon in EOEEs, which usually occurs during OS sleep and wakefulness, EME sleep period. There are two different types of BS patterns, namely early BS and late BS[7, 9]. As for the definition of early BS and late BS, it is not very clear at present. Yoshitomi thought that it should be divided according to the age of one month[9]. It is believed that the appearance in the early infancy is related to asymmetric BS pattern, but the appearance in late infancy is related to symmetric BS characteristics. This study did find that BS is not only found in OS, but also in other non-syndromic EOEE. This study provides an in-depth understanding of the genetic factors of EOEE-BS and explains the important role of genetic factors in addition to common causes such as cortical malformations. In this study, pathogenic mutations were identified, accounting for 7.6% (9/118). This study found that the largest genetic subgroup of EOEE-BS is the subgroup with KCNQ2 mutations, accounting for 66.7% (6/9). These 9 patients in this group had various types of seizures. The treatment effect and prognosis were poor. For the early onset of persistent tonic, spasm seizures and other types of intractable seizures, seizures with early EEG-BS performance may suggest the possibility of KCNQ2 pathogenic mutations. However, EOEE-BS is highly heterogeneous in terms of genetic etiology. Except for the largest genetic KCNQ2 subgroup, the second is SCN2A subgroup. For these 2 patients in this study, EEG was temporarily suppressed during sleep at 4 months and 5 months, and disappeared at 7 months. The reason for transient BS in SCN2A subgroup is unknown, which may be related to the immaturity of the central nervous system or gene mutation leading to brain dysfunction at this stage. 1 patient of STXBP1 subgroup was found in the third genetic subgroup. EOEE related to STXBP1 gene mutation has been mostly reported, and the common phenotype is OS. Mutations in the STXBP1 gene can cause abnormal neurotransmitter release, and cause brain stem cell apoptosis and dysfunction, change the excitability of neurons, and cause seizures[10]. This study find that EOEE-BS usually response poorly to AEDS.

Symptoms of dyskinesia include dystonia, chorea, paroxysmal dyskinesia, Parkinson's syndrome, ataxia, tremor and so on. At first, EOEEs with dyskinesia were focused on by Guerrini[11], who first reported ARX gene mutation associated with dyskinesia. And then STXBP1, FOXG1, CDKL5 related dyskinesia were gradually reported[1214]. Kobayashi reported 11 cases of infantile dyskinesia associated with EOEE. 9 cases were definitely diagnosed with epilepsy syndrome including WS[6]. In this study, 7 cases of EOEEs with dyskinesia were found. The onset age of dyskinesia ranged from 1 month to 1 year. 3 patients were diagnosed as epilepsy syndrome, namely WS, GLUT1 deficiency syndrome, EME. In this study, the main clinical symptoms of dyskinesia were dystonia, chorea and ataxia. Genetic mutations included CDKL5, SLC2A1, STXBP1, TBC1D24 and GRIA4. Our findings indicate 4 patients wtih dystonia received a good effect with Baclofen. 1 patient of STXBP1 encephalopathy with dystonia showed good response with LEV. This study find that with the control of epileptic seizures, the symptoms of dyskinesia in a few patients were also relieved.

SMC1A mutations can cause early onset epilepsy only in females with cluster seizures. At present, a spectrum of SMC1A gene have been related with Cornelia de Lange syndrome (CdLS), SMC1A-related encephalopathy only with female patients, colorectal carcinomas, bladder cancer and leukemia[1522]. Consistent with previous clinical reports, our 3 patients have moderate to severe neurological impairment and epilepsy. The seizures usually start in infancy. The presence of cluster seizures is an obvious characteristic. Although a minority of variants have also been found pathogenic, there is no clear relationship between severity of clinical phenotype and mutation types of truncation and missense variants[23]. However, the therapy strategy is still challenging. Among them, most patients show drug-resistant. All our 3 patients became seizure-free when KD was used as add-on therapy. There is evidence to show a relationship between SMC1A-mutated CdLS cell lines and oxidative stress[24]. KD in children with refractory epilepsy has also been demonstrated to improve mitochondrial function and decrease oxidative stress[25, 26]. Therefore, we speculate that KD add-on therapy reduces seizures by down-regulating the level of oxidative stress when combined with AEDS.

HNRNPU locating at chromosome 1, encodes heteronuclear ribonucleoprotein u. It is expressed in adult brain, heart, kidney and liver, especially in cerebellum. Firstly, it was reported related to 1q43-q44 deletion syndrome[27]. Later, a variety of clinical phenotypes related to HNRNPU mutation were reported, mainly including early-onset epilepsy with severe mental retardation, WS, EOEE, Lennox Gastaut syndrome and craniofacial deformity[2830]. Durkin thought that HNRNPU gene mutation related disease is more likely to be a kind of neurodevelopmental syndrome[30]. Durkin reported 21 cases of children, of which 3 cases were onset with febrile convulsion. Combined with 1 case in this study, we think that EOEEs onset with febrile convulsion is a special phenotype of HNRNPU related neurodevelopmental syndrome, similar to DS.

These responsible genes and their functions are mainly classified as: genes responsible for ion channels, genes responsible for the synapsis, neurotransmitters, and receptors, genes responsible for signal transduction, genes regulating DNA and RNA, genes responsible for the organelles and cell membrane, genes responsible for the development and growth of the neurons[31]. In this study, we find the ion channel gene mutations are the most common, representing the largest proportion (66/118, 55.9%). Among them, sodium channel gene mutations represent the largest proportion (47/66, 71.2%). In WS, we detect SCN3A, SCN2A, SCN8A, CACNA1H, DEPDC5, MECP2, DYNC1H1, CDKL5, ALG11, CCDC88C, GABAA1, IL1RAPL1, RNASEH2B, SLC19A3, STXBP1, RARS2, COL4A2 mutations. In addition to common gene mutations, we report rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B and COL4A2 in WS. In non-syndromic genetic causes of EOEEs, we detect rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A. As for genetic modes, denovo heterozygous mutations account for the largest proportion, 88.1% (104/118). Among these types of mutations, missense mutations represent the largest proportion, 68.6%(81/118). As expected, some of the genes are included in more than one group of the classification, as they have multiple functions.

Generally, genetic causes of EOEEs response poorly to AEDS treatment. However, we find that some gene mutation related EOEEs receive a good effect on specific AEDS. Besides the effect of KD is sure on the treatment of SMC1A encephalopathy. We also find that VPA added treatment shows a good effect on KCNB1 and PACS2 encephalopathy, LEV added treatment shows a good effect on STXBP1 encephalopathy, OXC added treatment shows a good effect on SCN8A encephalopathy.

VPA is a broad-spectrum antiepileptic drug, which exerts its anticonvulsant effect through a variety of mechanisms. VPA promotes the synthesis and release of gamma aminobutyric acid (GABA) through presynaptic and postsynaptic mechanisms, thereby increasing GABA mediated inhibition[32, 33]. VPA can regulate the expression of endoplasmic reticulum stress proteins (GRP78, GRP94 and calreticulin). It proves that VPA can inhibit excessive endoplasmic reticulum stress, reduce neuronal apoptosis and play a neuroprotective role in acute epileptic seizures[3436]. VPA can also regulate the level of intracellular Ca2+ by increasing the expression of endoplasmic reticulum stress protein, improve the calcium binding ability of endoplasmic reticulum, and enable cells to adapt to the cellular stress caused by the imbalance of intracellular Ca2+ homeostasis[36]. PACS2 plays an important role in controlling endoplasmic reticulum (ER) - mitochondrial communication, including the connection between mitochondria and ER and the homeostasis of ER. PACS2 is necessary for effective Ca2+ transfer between endoplasmic reticulum and mitochondria, while GRP78 is involved in Ca2+ transport from endoplasmic reticulum to mitochondria[3739]. Both of them play an important role in maintaining endoplasmic reticulum mitochondrial Ca2+ homeostasis. Therefore, we speculate that VPA may not only increase the concentration of GABA neurotransmitter and inhibit the voltage-gated Na+ channel, but also play a role by enhancing Akt phosphorylation, inhibiting endoplasmic reticulum stress and regulating intracellular Ca2+ level in children with PACS2 encephalopathy.

Certainly, knowing the pathophysiology of the underlying gene defect will help to pave the way for possible future individualized treatments. The limitations of our study are the small number of rare genes. Further research should include a larger cohort to validate our observations. We will continue to study and explore the detailed mechanism between rare gene mutation and seizure outcome.

5. Conclusion

We describe the clinical features and long-term outcome of genetic causes of EOEEs. The clinical manifestations of EOEE are variable, including dyskinesia. EOEE-BS usually responds poorly to AEDS therapy. Although some patients achieve seizure-free, there is no remarkable improvement in their development. EOEEs starting with febrile convulsion may be a special phenotype of HNRNPU related neurodevelopmental syndrome, similar to DS. We find the ion channel gene mutations are the most common. We report rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B and COL4A2 in WS and detect rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A in non-syndromic genetic causes of EOEEs. Although genetic causes of EOEEs response poorly to AEDS treatment, we find that some gene mutation related EOEEs receive good effects on specific AEDS.

Abbreviations

P=Patient; y=Year/Years; d=Day; m=Month/Months; F=Female; M=Male; FS=focal seizures; GTCS=generalized tonic-clonic seizures; T=Tonic seizures; SE=Status epilepticus; S=Spasm; AA=Atypical absence; M=Myoclonic; EPC= Epilepsia partialis continua

N=Normal; AH=Atypical hypsarrhythmia; H=Hypsarrhythmia; Frequent=Frequent multiple and multifocal sharp waves, spike waves, sharp slow waves or spike slow waves; Infrequent=Infrequent sharp waves, spike waves, sharp slow waves or spike slow waves; BS=Burst suppression; LEV=levetiracetam; TPM=topiramate; VPA=valproate; LTG=lamotrigine; OXC=oxcarbazepine; KD=Ketogenic diet; PB=Phenobarbital; VNS=Vagus nerve stimulation; P=Prednisone; LCM=Lacosamide; MP=Methylprednisolone; CZP=Clonazepam; B6=Vitamin B6; NZP=Nitrazepam; VGB=Vigabatrin; QD=Quinidine; CLB=Clobazam; BAL=Baclofen; WG=Widen gap in extracerebral space.

Declarations

Acknowledgement

We appreciate all the patients and their guardians participating in this study. And I express my heartfelt gratitude for the hard work of all team members.

Ethics approval and consent to participate

The project ethics were approved by Ethic Committees of Children’s Hospital of Fudan University. All the experiment protocol for involving humans was in accordance to guidelines of national/international/institutional or Declaration of Helsinki.

Authors’ contributions

Chunhui Hu wrote the main manuscript text. Deying Liu and Tian Luo prepared figures and tables. Zhisheng Liu drafted the manuscript. Yi Wang revised the manuscript. All authors reviewed the manuscript.

Funding

The project was supported by Shanghai Municipal Science and Technology Major Project (Grant No. 2017SHZDZX01).

Availability of data and materials

The data that support the findings of this study are available from the authors upon reasonable request. The results/data/figures in this manuscript have not been published elsewhere, nor are they under consideration by another publisher.

Consent for publication

Written informed consent was obtained from all the patient’s parent for the publication.

Competing interests

None of all authors have any disclosures to make in relation to this manuscript.

References

  1. Fisher RS, Acevedo C, Arzimanoglou A, et al. ILAE Official Report: A practical clinical definition of epilepsy. Epilepsia. 2014, 55 (4): 475–482.
  2. Gürsoy S,Erçal D. Diagnostic Approach to Genetic Causes of Early-Onset Epileptic Encephalopathy. Journal of Child Neurology. 2015, 31 (4): 523–532.
  3. Hwang S-K,Kwon S. Early-onset epileptic encephalopathies and the diagnostic approach to underlying causes. Korean Journal of Pediatrics. 2015, 58 (11): 407–14.
  4. Allen NM, Conroy J, Shahwan A, et al. Unexplained early onset epileptic encephalopathy: Exome screening and phenotype expansion. Epilepsia. 2016, 57 (1): e12-e17.
  5. Zhang Q, Li J, Zhao Y, et al. Gene mutation analysis of 175 Chinese patients with early-onset epileptic encephalopathy. Clinical Genetics. 2017, 91 (5): 717–724.
  6. Kobayashi Y, Tohyama J, Kato M, et al. High prevalence of genetic alterations in early-onset epileptic encephalopathies associated with infantile movement disorders. Brain and Development. 2016, 38 (3): 285–292.
  7. Olson HE, Kelly M, LaCoursiere CM, et al. Genetics and genotype-phenotype correlations in early onset epileptic encephalopathy with burst suppression. Annals of Neurology. 2017, 81 (3): 419–429.
  8. Lee S, Kim SH, Kim B, et al. Genetic diagnosis and clinical characteristics by etiological classification in early-onset epileptic encephalopathy with burst suppression pattern. Epilepsy Research. 2020, 163: 106323.
  9. Yoshitomi S TY, Imai K, Koshimizu e, Miyatake S. Different types of suppression-burst patterns in patients with epilepsy of infancy with migrating focal seizures(EIMFS). Seizure. 2019, 65: 118–123.
  10. McTague A, Howell KB, Cross JH, et al. The genetic landscape of the epileptic encephalopathies of infancy and childhood. Lancet Neurol. 2016, 15(3): 304–16.
  11. Guerrini R, Moro F, KatoM, et al. Expansion of the first PolyA tract of ARX causes infantile spasms and status dystonicus. Neurology. 2007, 69(5): 427–33.
  12. Deprez L, Weckhuysen S, Holmgren P, et al. Clinical spectrum of early-onset epileptic encephalopaties associated with STXBP1 mutations. Neurology. 2010, 75(13): 1159–65.
  13. Milh M, Villeneuve N, Chouchane M, et al. STXBP1-related encephalopathy presenting as infantile spasms and generalized tremor in three patients. Epilepsia. 2011, 52(10): 1820–7.
  14. Renzo Guerrini,Parrini E. Epilepsy in Rett syndrome, and CDKL5- and FOXG1-gene-related encephalopathies. Epilepsia. 2012, 53(12): 2067–78.
  15. Wenger TL, Chow P, Randle SC, et al. Novel findings of left ventricular non-compaction cardiomyopathy, microform cleft lip and poor vision in patient with SMC1A-associated Cornelia de Lange syndrome. Am J Med Genet A. 2017, 173 (2): 414–420.
  16. Symonds JD, Joss S, Metcalfe KA, et al. Heterozygous truncation mutations of theSMC1Agene cause a severe early onset epilepsy with cluster seizures in females: Detailed phenotyping of 10 new cases. Epilepsia. 2017, 58 (4): 565–575.
  17. Huisman S, Mulder PA, Redeker E, et al. Phenotypes and genotypes in individuals with SMC1A variants. Am J Med Genet A. 2017, 173 (8): 2108–2125.
  18. Balbas-Martinez C, Sagrera A, Carrillo-de-Santa-Pau E, et al. Recurrent inactivation of STAG2 in bladder cancer is not associated with aneuploidy. Nat Genet. 2013, 45 (12): 1464–9.
  19. Sarogni P, Palumbo O, Servadio A, et al. Overexpression of the cohesin-core subunit SMC1A contributes to colorectal cancer development. J Exp Clin Cancer Res. 2019, 38 (1): 108.
  20. Thol F, Bollin R, Gehlhaar M, et al. Mutations in the cohesin complex in acute myeloid leukemia clinical and prognostic implications. Blood. 2014, 123 (6): 914–20.
  21. Musio A. The multiple facets of the SMC1A gene. Gene. 2020, 743 144612.
  22. Jansen S, Kleefstra T, Willemsen MH, et al. De novo loss-of-function mutations in X-linked SMC1A cause severe ID and therapy-resistant epilepsy in females: expanding the phenotypic spectrum. Clin Genet. 2016, 90 (5): 413–419.
  23. Oguni H, Nishikawa A, Sato Y, et al. A missense variant of SMC1A causes periodic pharmaco-resistant cluster seizures similar to PCDH19-related epilepsy. Epilepsy Res. 2019, 155 106149.
  24. Cukrov D, Newman TAC, Leask M, et al. Antioxidant treatment ameliorates phenotypic features of SMC1A-mutated Cornelia de Lange syndrome in vitro and in vivo. Hum Mol Genet. 2018, 27 (17): 3002–3011.
  25. Pinto A, Bonucci A, Maggi E, et al. Anti-Oxidant and Anti-Inflammatory Activity of Ketogenic Diet: New Perspectives for Neuroprotection in Alzheimer's Disease. Antioxidants (Basel). 2018, 7 (5): 63.
  26. Lima PA, Sampaio LPdB,Damasceno NRT. Ketogenic diet in epileptic children: impact on lipoproteins and oxidative stress. Nutritional Neuroscience. 2015, 18 (8): 337–344.
  27. Thierry G, Bénéteau C, Pichon O, et al. High-resolution array CGH defines critical regions and candidate genes for microcephaly, abnormalities of the corpus callosum, and seizure phenotypes in patients with microdeletions of 1q43q44. Hum Genet. 2012, 131(1): 145–56.
  28. Leduc MS, Chao H-T, Qu C, et al. Clinical and molecular characterization of de novo loss of function variants inHNRNPU. American Journal of Medical Genetics Part A. 2017, 173 (10): 2680–2689.
  29. Bramswig NC, Lüdecke H-J, Hamdan FF, et al. Heterozygous HNRNPU variants cause early onset epilepsy and severe intellectual disability. Human Genetics. 2017, 136 (7): 821–834.
  30. Durkin A, Albaba S, Fry AE, et al. Clinical findings of 21 previously unreported probands with HNRNPU related syndrome and comprehensive literature review. American Journal of Medical Genetics Part A. 2020, 182 (7): 1637–1654.
  31. Nashabat M, Qahtani XSA, Almakdob S, et al. The landscape of early infantile epileptic encephalopathy in a consanguineous population. Seizure. 2019, 69: 154–172.
  32. Johannessen CU,SI J. Valproate past, present, and future. CNS Drug Rev. 2003, 9(2): 199–216.
  33. Romoli M, Mazzocchetti P, D'Alonzo R, et al. Valproic Acid and Epilepsy From Molecular Mechanisms to Clinical Evidences. Curr Neuropharmacol. 2019, 17(10): 926–946.
  34. Bown CD, Wang JF, Chen B, et al. Regulation of ER stress proteins by valproate therapeutic implications. Bipolar Disord. 2002, 4(2): 145–51.
  35. Li Z, Wu F, Zhang X, et al. Valproate Attenuates Endoplasmic Reticulum Stress-Induced Apoptosis in SH-SY5Y Cells via the AKT/GSK3β Signaling Pathway. International Journal of Molecular Sciences. 2017, 18 (2): 315.
  36. Fu J, Peng L, Wang W, et al. Sodium Valproate Reduces Neuronal Apoptosis in Acute Pentylenetetrzole-Induced Seizures via Inhibiting ER Stress. Neurochemical Research. 2019, 44 (11): 2517–2526.
  37. Simmen T, Aslan JE, Blagoveshchenskaya AD, et al. PACS-2 controls endoplasmic reticulum–mitochondria communication and Bid-mediated apoptosis. The EMBO Journal. 2005, 24 (4): 717–729.
  38. Thomas G, Aslan JE, Thomas L, et al. Caught in the act – protein adaptation and the expanding roles of the PACS proteins in tissue homeostasis and disease. Journal of Cell Science. 2017, 130 (11): 1865–1876.
  39. Veeresh P, Kaur H, Sarmah D, et al. Endoplasmic reticulum–mitochondria crosstalk: from junction to function across neurological disorders. Annals of the New York Academy of Sciences. 2019, 1457 (1): 41–60.