FS (with or without subsequent epilepsy), we identified 2 other frameshift mutations (p.Val462fs*33 and p.Pro59fs*12), 1 nonsense mutation (p.Arg136*), 1 missense mutation (p.Met199Val), and 1 deletion (exons 1–4) in the GABRG2 gene. Most patients carrying a GABRG2 mutation had a reported history of FS (22/23), associated with TLE in 1 family (family A), generalized epilepsy with absences and GTCS in 2 families (families E and F), and undefined epilepsy with TCS and episodes of loss of consciousness in 1 family (family D). GABRG2 mutations segregated predominantly with FS, indicating that GABRG2 mutations are drivers of the FS phenotype, rather than epilepsy. As expected with common traits, several affected family members did not carry a GABRG2 mutation: 3 family members without a history of FS (B/IV-5, B/IV-7, and B/IV-9) and 2 phenocopies (individuals A/II-9 and C/II-1). Overall, the penetrance of GABRG2 mutations was high in our cohort, with only one asymptomatic carrier (individual A/I-2). It should be noted though that a history of FS may have been underreported in this generation. The relatively high frequency (5.6%) of GABRG2 mutations compared with previously published data24,28,30 is most probably linked to the fact that FS segregating as an autosomal dominant trait was a
