 It is also unclear how this membrane hypoexcitability leads to the GEFS+ phenotype.Patients with GEFS+ type 3 have mutations in the GABRG2 gene, which encodes the GABAA γ2 subunit (figure 2).The first mutation discovered in GABRG2 was K289M, in the extracellular region linking membrane-spanning domains M2 and M3.