EFHC1 mutation in Indian juvenile myoclonic epilepsy patient

Abstract

Objective: Juvenile myoclonic epilepsy (JME) is the most common form of idiopathic generalized epilepsies (IGEs) and is genetically heterogeneous. Mutations in EFHC1 cause JME. Because about 2 million people in India are affected by JME alone, we investigated the prevalence of mutations in the EFHC1 gene in the Indian population with JME. We studied 63 patients with JME and 80 healthy controls.

Methods: Clinical identification of JME was evaluated using established criteria. Following clinical evaluation of the patients and confirming presence of JME, blood samples were collected from each patient and healthy individual. Subsequently, genomic DNA was extracted from the blood samples. Eleven exons of the EFHC1 gene were individually amplified by polymerase chain reaction (PCR) for each DNA sample. The PCR products were then purified and sequenced commercially. The identified DNA variants were sequenced at least twice in both the forward and reverse directions and compared with the Exome Aggregation Consortium (ExAC) database.

Results: We found five heterozygous and one homozygous variant. We found three novel coding variants 661C→T, 779 G →A, and 730 C→T, which lead to R221C, R260Q, and R244STOP amino acid substitutions, respectively. The coding variant 475 C→T, resulting in the amino acid substitution R159W, reported earlier as polymorphism, was also identified in both patient and control populations.

Significance: Detection of these three novel variants, excluding R159W, which is considered polymorphism, expands the range of possible mutations in the EFHC1 gene. The novel variants that we are reporting herein have not been mentioned before as occurring in JME patients of other ethnic population. Therefore, these novel coding variants may be confined to the Indian JME population. Further studies on the mutational spectrum of EFHC1 in a larger number of Indian JME patients concurrent with their mode of inheritance and underlying functional assays should establish whether EFHC1 could be a panethnic gene for JME.

Keywords: EFHC1; Indian population; JME; Mutation; Polymorphism.

Figure 1

Chromatogram of the five EFHC1 variants. (A) WT and (B) R260Q; (C) WT and (D) R244STOP; (E) WT and (F) R221C; (G) WT and (H) R294H; (I) WT and (J) & (K) R159W (homozygous and heterozygous, respectively)

Figure 2

(A) Schematic diagram of EFHC1 protein. (B) Genomic organization of the EFHC1 gene showing the previously reported mutations in different exons, whereas the new mutations observed in the Indian JME patient are shown in bold type.

Figure 3

Pedigrees of the families with JME: (A) R294H and (B) R159W. Filled symbols indicate affected individuals. Arrows indicate the probands of each family.