Severe carbamazepine-induced drug reaction and whole genome analysis: case report

Carbamazepine is an important treatment for epileptic disorders, bipolar disorder and trigeminal neuralgia. However, some patients would suffer from cutaneous adverse drug reactions (cADRs) after taking it. At present, the carbamazepine-induced drug reaction has a great relationship with genetic diversity. The present study reported a patient who presented with rash after starting carbamazepine, and a whole genome analysis was reported.


Abstract
Background Carbamazepine is an important treatment for epileptic disorders, bipolar disorder and trigeminal neuralgia. However, some patients would suffer from cutaneous adverse drug reactions (cADRs) after taking it. At present, the carbamazepine-induced drug reaction has a great relationship with genetic diversity. The present study reported a patient who presented with rash after starting carbamazepine, and a whole genome analysis was reported.
Case presentation A 17-year-old girl was transferred to our Neurology Department with symptoms of painful neck and seizures. Skull computerized tomography (CT) revealed subarachnoid hemorrhage. Electroencephalogram (EEG) revealed sharp waves, spikes slow waves and sharp slow waves. The clinical diagnosis of subarachnoid hemorrhage and symptomatic epilepsy were made through a series of inspections. Carbamazepine was administered.
The patient presented with rash at six days after starting carbamazepine, and presented with a striking clinical drug reaction. Hence, a whole genome analysis was carried out.

Discussion
The result revealed that the mutation of Met1080Val in the SCN4A gene was associated with the carbamazepine-induced drug reaction. However, this conclusion needs to be confirmed by a large number of clinical data and related functional mechanisms.

Background
Carbamazepine is an extensive prescription drug that is used not only as a first-line 3 antiepileptic drug, but also for the treatment of trigeminal and bipolar disorders [ 1,2].
Although this is generally well-tolerated, up to 10% of patients would suffer from cutaneous adverse drug reactions (cADRs) [2]. These cADRs can be classified as light or heavy. Light cADRs include maculopapular eruption (MPE), while heavy cADRs include hypersensitivity syndrome (HSS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). The morbidity rate of heavy cADRs are low, but the mortality rate can reach as high as 40% [3]. In the present study, a patient presented with carbamazepineinduced drug reaction, and a whole genome analysis was reported. Furthermore, the detailed neurological examination revealed that the patient had low consciousness, and the remaining examination results were normal.

Case Presentation
The skull computerized tomography (CT) revealed subarachnoid hemorrhage (Fig. 1). Digital 4 subtraction angiography (DSA) exhibited poor development of the right transverse sinus in the venous phase, but no significant abnormal signs were seen in the remaining brain vessels (Fig. 2). Electroencephalogram (EEG) revealed sharp waves (120-150 μV, 5 Hz), spikes slow waves and sharp slow waves (110-280 μV, 2-3 Hz) (Fig. 3). The laboratory results revealed that the complete blood count, blood sedimentation rate, electrolytes, liver-function test, renal-function test, urine routine and stool routine were generally normal.
On the first day, carbamazepine was administered (50 mg, thrice daily) to prevent further Then, the patient presented with sore throat, especially after eating and drinking, and fever. Afterwards, the rash progressed to the arms, chest and back on the 13th day ( Fig.   4a). The examination revealed that the patient's temperature was 37.7℃. The investigation reports revealed an elevated blood sedimentation rate. Carbamazepine was immediately stopped, and the patient was treated by topical antiallergic agents. However, within the next two days, the soreness of throat was aggravated with generalized rash all over the body, followed by hyperemic conjunctivae (Fig. 4b). Hence, the patient was started on tapering doses of steroids. The patient's skin symptoms and laboratory abnormalities started improving on the 24th day of hospitalization (Fig. 4c-d). The related inspections were completed, such as ultrasonic cardiogram (UCG) and brain magnetic resonance imaging (MRI). All inspections results were generally normal. The patient was discharged from hospital on the 30th day after admission.
The methods for the whole exome sequencing (WES) for exome capture, exon-enriched DNA library construction, sequencing, genotyping and variant analysis has been previously reported [4]. The DNA was extracted from blood using QIAamp DNA Kit (Qiagen). conducted a study on the HLA-A*3101 allele and found that 60.7% of the patients had carbamazepine-induced cADRs in Japan, while only 12.5% were carbamazepine-tolerant controls. In addition, they implied that the HLA-A*3101 allele was a risk predictor of carbamazepine-induced cADRs with 60.7% sensitivity and specificity, which could reach 87.5% [6]. Other gene polymorphisms were also closely correlated to the carbamazepine- However, it is well-known that the mechanism of drug reaction is mainly associated with the drug-induced immune response. Drugs, as small molecules, belong to semi-antigens, which cannot cause immune response. The T-cell-mediated immune response be activated by combining with proteins or other vectors to form a complete antigen in vivo, or becoming a precursor substance with antigenic determinant after liver metabolism. In vitro, the druginduced proliferation of peripheral blood mononuclear cells (PBMC) from patients allergic taking carbamazepine confirmed the involvement of drug-specific T-cells in drug allergies [9]. Wu et al. revealed that carbamazepine-specific CD4+, CD8+ and CD4+CD8+ T-cells were found in the peripheral circulation of five hypersensitive patients by using modified cloning methodologies [10]. Furthermore, the great majority of carbamazepine-specific clones express CD4+ T-cells and approximately 10% of clones express CD8+ T-cells [11,12]. The cells involved in carbamazepine-induced MPE immune response were mainly CD4+ T-cells [11]. While a large number of CD8+ T-cells were found in carbamazepine-8 induced TEN [13]. Therefore, the carbamazepine-induced drug reaction mediates immune response by activating CD4+ T-cells or CD8+ T-cells.
The SCN4A gene encodes the alpha subunit of the skeletal muscle sodium channel. The alpha subunit, which is a transmembrane glycoprotein, is mainly distributed in skeletal muscle, and is responsible for regulating the generation and transmission of skeletal muscle action potentials. The present literature reported that the SCN4A gene mutation mainly led to myotonic myopathies and periodic paralysis PP . Matthews et al. found that there were more than 20 SCN4A gene mutation sites associated with paramyotonia congenita (PMC) by summing up the HGMD database and the hotspot mutation regions were located in the 22th and 24th exon [14]. Furthermore, there was close relationship between paralysis periodica paramyotonica (PPP) and SCN4A mutations, such as Met1592Val, Arg1448Cys and so on [15,16]. Bugiardini et al. first reported that the variant c.215C>T (p.Pro72Leu) in the SCN4A gene was correlated to myotonic dystrophy type-2 (DM2) [17]. Previous studies had found that many SCN4A gene mutations were associated with hyperkalemic periodic paralysis (HyperKPP), such as Thr704Met, Ala1156Thr, Met1360Val, Ile1495Phe, Met1592Val and so on [18][19][20][21][22]. It was also revealed that Thr704Met, Metl592Val, Val-781lle and Arg675Gln mutations were correlated to normokalemic periodic paralysis (NormoKPP) in Chinese families, but there were no differences in the phenotype of these types of mutations and less reporting [23,24]. Similarly, hypokalemic periodic paralysis (HypoKPP) was closely associated with SCN4A mutations, such as R669H, R1135H, R1132Q, P1158S and so on [25][26][27]. Except for myotonic myopathies and periodic paralysis, SCN4A gene mutations can lead to other illness. Bergareche et al. performed whole exome sequencing analyses in a large Spanish family with essential tremor (ET) , and found that the genetic variability of SCN4A was associated with the development of ET [28]. 9 It is known that T-cell developing from immature CD4+CD8+ double-positive thymocyte to mature CD4 or CD8 single-positive stage requires proper T-cell receptor (TCR) signaling.
Recent research has confirmed that proteins and miRNAs were correlated to specialized regulators of TCR signaling operating during thymocyte development. A voltage-gated Na+ channel (VGSC) is one of important regulators during positive selection [ 29]. The VGSC offered a mechanism for the calcium signal, and responded to weak ligands in the ability of immature thymocyte [29,30], which enable CD4+T cells and CD8+T cells to mature and participate in the immune response. There were 11 genes (SCN1A-SCN11A) encoding a family of nine functionally expressed voltage-gated sodium channels in mammals [31]. It was speculated that SCN4A mutations would increase the activity of the calcium signal and proliferate the CD4+T cells and CD8+T cells, which would lead to the drug reaction.
The mechanism of carbamazepine-induced drug reaction remains unclear. The hottest research is the relationship between genetic diversity and drug reaction. The determination of whether the Met1080Val mutation of the SCN4A gene is associated with the carbamazepine-induced drug reaction still needs to be confirmed through a large number of clinical data and related functional mechanisms. It has important significance for patients to take carbamazepine.

Declarations
Ethics approval and consent to participate Not applicable.
Consent to publish 10 Written informed consent was obtained from the patient's parents for publication of this case report and any accompanying images.

Availability of data and material
All data containing relevant information to support the study findings are included in the manuscript.

Figure 4
Rash of patient. a The rash of arm on the 13th days. b The rash of leg on the 15th days. c,d The rash of head face and back on the 24th days.

Supplementary Files
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