We performed whole-exome sequencing on 3 affected family members (A/II-1, A/II-4, and A/II-9). Originally, a 20 cM spaced genome-wide microsatellite analysis was suggestive of a locus on chromosome 18qter and a probable second locus on chromosome 1q25-q31 with maximum pairwise LOD scores of 3.04 and 2.33, respectively.19 We first focused the analysis on these 2 regions, then on the rest of the exome dataset. According to our filtering criteria, only 7 variants were common to all 3 siblings, but none of the corresponding genes (ABL2, BOD1L1, B3GALT4, EXO1, HERC4, OR5K1, or SSH2) were functionally candidate for epilepsy or expressed in the brain. We therefore subsequently restricted the analysis to the exome datasets of individuals A/II-1 and A/II-4, who belong to the same branch of the family. We identified a heterozygous deletion/insertion mutation (c.1206delinsTTCAT) in exon 9 of the γ2 subunit of the GABAA receptor gene GABRG2 gene (located on chromosome 5) in both A/II-1 and A/II-4. Sanger sequencing indicated that the p.Glu402fs*3 variant was segregated within all affected family members of the first branch, but was not present in individual
