The patient was a 3 years old female who presented to Myelin Disorders Clinic due to progressive neurologic regression which was first noticed at the age of 18 months. She was the only child of a consanguineous parent which was born at 39 weeks of gestational age through a Cesarean section following an uneventful delivery with birth weight and head circumference of 3550 grams (Z-Score: +1SD) and 35.5cm (Z-Score: +1SD), respectively. Her mother had received good prenatal care without any significant problems. The patient achieved her developmental milestones normally until the age of 5-6 months. At this age, she had acceptable social interactions and was able to hold her head up, could sit with one hand support, say mama and dada, and was able to recognize her parents. Since then, developmental arrest and neurologic regression began firstly by feeding and swallowing problems, four limbs dystonia, severe para-spinal muscles spasm and dystonia causing severe opisthotonus followed by scissoring position and spasticity in lower limbs. At the age of 1.5 years, she needed to be supported significantly in order to sit. The maximum speech ability was not exceeding 2-3 incomplete words’ expression and she had several problems with feeding and swallowing as she was fed with mixed ground foods and clear drinks. She had undergone several occupational therapy sessions which were ordered by her primary care physician. She faced remarkable and more rapid neurologic regression after routine vaccination at the age of 18 months, which led to considerable feeding difficulties, the inability of words expression, and poor head and neck control. Then, she was referred to our clinic. On examination, she had low set ears, high arch palate and beaked nose, flat nasal bridge, and thick eyebrows in addition to significant four limbs dystonia, truncal hypotonia, and a noticeable degree of spasticity in her distal parts of both upper and lower limbs.
Upon the follow-up visit at 27 months of age, her main clinical findings were four limbs spasticity, severe generalized dystonia, hyperreflexia with +3 deep tendon reflexes (DTRs), and upward plantar reflex. Her weight was 8kg (less than 3rd centile, Z- Score: -3SD) and HC was 47 cm (Z-Score: 0SD). She was taking the following medications: diazepam, tizanidine, baclofen, melatonin, and trihexyphenidyl.
Basic metabolic tests indicated a high plasma lactate level of 39.7 mmol/L (NL<16mmol/L), while the results of serum ammonia, homocysteine, metabolic screen (MS/MS) were all normal.
The first brain magnetic resonance imaging (MRI) which was done at the first visit showed abnormal deep white matter signal changes especially in posterior periventricular area of T2-Weighted and FLAIR sequences, deepening of the Sylvain fissures, mild supratentorial atrophy, in addition, to exvacue ventriculomegaly (Figure 1, 1A, 1C-white arrows), the near-normal appearance of T1-Weighted sequence (Figure 1, 1B), and thinning of the corpus callosum (Figure 1, 1D).
Imaging findings in the second brain MRI at the age of 27 months were similar to the first MRI but the severity of atrophy had increased in both the supratentorial area and cerebellar vermis (not shown).
According to the progressive patient’s clinical scenario, normal basic metabolic studies, and parents’ consanguinity, Whole Exome Sequencing (WES) was considered to diagnose a possible underlying neurodegenerative disease. In the follow-up visit, at the age of 29 months, her parents reported infrequent focal seizures, therefore; levetiracetam was prescribed for her to control the seizures. The patient was admitted into the hospital with clinical manifestations of aspiration pneumonia at the ages of 32 and 35 months due to a progressive worsening of her feeding condition. During the second hospitalization, her spasms and dystonia were aggravated which led to severe respiratory distress and admission to the pediatric intensive care unit (PICU) and tracheal intubation. The laboratory tests showed a high serum lactate level of 39 mmol/L (NL<16mmol/L), again, while serum ammonia, homocysteine, arterial blood gas (ABG), and cerebrospinal fluid (CSF) analysis results were normal. Electroencephalogram (EEG) revealed abnormal findings due to the appearance of generalized slowing and low-voltage background without any paroxysmal epileptiform discharge. These findings were compatible with a diffuse encephalopathic process pattern. Percutaneous endoscopic gastrostomy (PEG) was placed for the patient to facilitate her difficulty feeding within a short time after discharge.
Upon the last visit, at age of 36 months, her problems especially limbs spasticity and dystonia were still present but the feeding problem had been ameliorated though she had gained a weight of 300 grams over one month after discharge. Her seizures were controlled by oral levetiracetam and rectal diazepam as needed. Her weight was 9kg (Z-Score: -3SD) and her head circumference was 48cm (Z-Score: 0SD). Unfortunately, she died one month later due to cardiorespiratory arrest at home.
A 3-year-old male was referred to Myelin Disorders Clinic who exhibited developmental motor and speech regression which was started at 11 months of age without any precedent event.
He was born at 36 weeks of gestation after a trouble-free vaginal delivery from a first cousin's parent. His birth weight and head circumference (HC) were 3700 grams (z-score +1) and 33 cm (z-score 0), respectively. The patient achieved neck holding at the age of 3 months, independent sitting at the age of 8 months, walking with support at the age of 11 months, and a few words expression and good social contact at the age of 12 months.
His parents had first noted limbs jerking movements during sleep at the age of 11 months that was treated by clonazepam. Then after he experienced progressive lower limbs spasticity and fine and gross motor regression succeeded by speech regression but cognition ability was partially spared.
On physical examination, he was alert with a HC of 49.5 cm (Z-score 0) and a weight of 14 kg (Z-score 0). He had an acceptable visual fix and follow, normal horizontal and vertical eye movements and normal pupils’ reaction to light and normal gag reflex. He had no dysmorphic feature. Cranial nerves examination was normal. Deep tendon reflexes of upper extremities were 3+ and lower extremities were 4+ with clonus. Plantar reflexes were bilaterally upward. Distal four limbs dystonia was also seen. He had a tripod sitting position. His gross motor ability was estimated 3 out of 5 based on Gross Motor Function Classification System (GMFCS) scale. The skin integrity was normal without any congenital or acquired rash. No organomegaly was detected.
His older brother had a similar clinical scenario which was started after a normal growth and developmental course until late infancy but after that, his motor and then speech milestones were regressed. Infrequent non-febrile seizures were started at the age of 3 years old. He eventually died after a deteriorative clinical course at 19 years of age with clinical presentations of severe appendicular spasticity, generalized dystonia, feeding problems, and respiratory failure. He had not diagnosed with any specific neurologic disorder in spite of extensive metabolic studies.
In proband case, basic laboratory and metabolic results including thyroid and liver function tests, serum ammonia and lactate, urine organic acid profiles, metabolic screen (MS/MS), and serum acylcarnitine profile were all normal. Electroencephalogram (EEG) and karyotype were both normal. Clonazepam, tizanidine, biotin, CoQ10, and Omega-3 syrup were prescribed for him and regular occupation therapy was started.
His brain MRI at the age of 18 months showed a faint increased signal intensity of white matter of the posterior periventricular area (Figure 1, 2 A, C-white arrows), and no significant finding in axial and sagittal T1-Weighted images (Figure 1, 2B).
The patient was a 20-month-old male who was referred to Myelin Disorders Clinic due to motor milestones delay and neurologic regression which was first noted at 6 months of age by his parents. He was born at term at 39 weeks of gestation through normal vaginal delivery from consanguineous parents. His mother had taken good prenatal care, however, she experienced preeclampsia during her final pregnancy trimester. The birth weight and head circumference (HC) of the patient were 3350 grams (Z-Score: 0SD) and 34cm (Z-Score: 0SD), respectively. Shortly after birth, he was admitted to the neonatal intensive care unit (NICU) due to a low APGAR score at five minutes of age, not crying, and possible birth asphyxia for a short-term period without the requirement to assisted ventilation and finally was discharged with the good general condition after two days.
After hospital discharge, limbs jerking movements were noticed during sleep by his parents which were diagnosed with neonatal sleep myoclonus by their family physician. They were stopped within a few days without treatment. In addition, he was admitted again due to exaggerated neonatal jaundice with indirect bilirubin of 17 mg/dl at the end of the first week of life which was treated by phototherapy. Given his developmental milestones, he achieved neck holding at age 2 months, rolling over at age 4-5 months, and starting to crawl at age 6 months.
Thereafter, the patient’s motor development stopped and motor regression commenced. His parents recognized that he lost his ability to crawl and using his legs especially the left foot, gradually. He was not able to sit even with support at 8 months old. As a result, firstly his parents visited a pediatric orthopedist, and then they were referred to a child neurologist for further investigation. Moreover, his pelvic x-ray was normal and he had no contracture, joint deformity, and obvious scoliosis. On neurologist examination at 9 months of age, lower limbs spasticity, hand fisting, increased deep tendon reflexes (DTR 3+) in lower limbs, and bilateral upward plantar reflex were detected. Ophthalmic examination included all directions’ gaze, fix and follow, reaction to light, and strabismus was normal. His weight and head circumference were 8kg (Z-Score: -1SD) and 45cm (Z-Score: 0SD), respectively. All biochemical and basic metabolic tests including serum creatine phosphokinase (CPK), thyroid, liver, and kidney function tests, uric acid level, plasma amino acid chromatography (HPLC), and alpha-1, 4 glucosidase enzyme activity level which was measured by dried blood spot (DBS) test were within normal limit. Occupational therapy was started and a follow-up visit was scheduled at 1 year old.
On review at age of 12 months, his motor ability had declined, significantly. He wasn’t able to crawl or roll over anymore. Furthermore, his lower limbs had become more spastic. He had acceptable social interactions and no significant feeding or swallowing problems, but, his speech and cognition skills progression were arrested according to his age. His weight, height and head circumference were 8.5kg (Z-Score: -1SD), 76cm (Z-Score: 0SD) and 46cm (Z-Score: 0SD), respectively. A brain and spinal MRI were done which were reported normal by a neuroradiologist (not shown).
Additional metabolic studies consisting of serum ammonia and lactate, metabolic screen (MS/MS), acylcarnitine, and urine organic acids profiles were all normal. Abdominal and pelvic ultrasonography revealed an ectopic right kidney in addition to horseshoe kidneys. Cardiologic and ophthalmologic consultations indicated no significant findings. Finally, Whole Exome Sequencing was done according to motor neurologic regression, speech, and cognitive delay, parents’ consanguinity, normal metabolic test results, and imaging study.
The second brain MRI which was done at 18 months old indicated delayed myelination of subcortical white matter in addition to abnormal signals of posterior periventricular white matter (Figure 1 3A, C-white arrows). The T1-Weighted sequence at the level of basal ganglia indicated no significant finding (Figure 1, 3B). Sagittal T1-weigted image showed mild thinning of corpus callosum and upper vermis (Figure 1D). Furthermore, electromyography and nerve conduction velocity studies (EMG-NCV) revealed generalized sensory polyneuropathy.
Data analysis of the called variants in the three unrelated families revealed the genetic etiology of affected individuals. Prioritization of variants led to the identification of three distinct homozygous variants in the ACER3 gene (NM_018367.7) which they were absent in public variant databases. Sanger sequencing confirmed the segregation of variants within the family members.
The c.53T>C variant found in patient P1 is residing at the first exon of ACER3 and 18th amino acid of the encoded protein. The c.292T>C variant (in patient P2) is affecting the exon 4 of this gene and results to a substitution in 98th residue of ACER3 protein. Both missense variants were similar regarding to their pathogenicity, which was predicted by in-silico pathogenicity prediction tools (Table 2). Examining the level of conservation at the protein level showed that these two variants possess high conservation from Humans to yeast. MUPro was also used to analyze the protein stability based on protein Delta G upon the mutation revealing that missense variants lead to diminished protein stability.
Unlike the other two missense variants, the third variant discovered in the P3 family was a nonsense variant creating a stop codon and depletion of downstream residues of ACER3 protein.
The available protein structure of ACER3 (6G7O) was utilized to study the interaction state of ACER3 in the normal and mutated form. The visualizations indicated that the interaction of Leu18 with the residues in its vicinity had no alteration after substitution to proline. In contrast, the other variant seemed to lost a strong hydrogen bond to Thr133 (2.7 Å) and made a bond with a neighboring water molecule (Figure 2B).