Novel homozygous, heterozygous and hemizygous FRMD7 gene mutations segregated in the same consanguineous family with congenital X-linked nystagmus

Congenital nystagmus (NYS) is characterized by bilateral, spontaneous, and involuntary movements of the eyeballs that most commonly presents between 2 and 6 months of life. To date, 44 different FRMD7 gene mutations have been found to be etiological factors for the NYS1 locus at Xq26-q27. The aim of this study was to find the FRMD7 gene mutations in a large eleven-generation Indian pedigree with 71 members who are affected by NYS. Mutation analysis of the entire coding region and splice junctions of the FRMD7 gene revealed a novel missense mutation, c.A917G, predicts a substitution of Arg for Gln at codon 305 (Q305R) within exon 10 of FRMD7. The mutation was detected in hemizygous males, and in homozygous and heterozygous states in affected female members of the family. This mutation was not detected in unaffected members of the family or in 100 unrelated control subjects. This mutation was found to be at a highly conserved residue within the FERM-adjacent domain in affected members of the family. Structure prediction and energetic analysis of wild-type FRMD7 compared with mutant (Q305R) revealed that this change in amino acid led to a change in secondary structure predicted to be an energetically unstable protein. The present study represents the first confirmation of FRMD7 gene mutations in a multigenerational Indian family and expands the mutation spectrum for this locus.