Digenic inheritance of a ROM1 gene mutation with a peripherin/RDS or rhodopsin mutation in families with retinitis pigmentosa

Two families with retinitis pigmentosa showed inheritance of an Arg-16-His ROM1 gene mutation with either an Arg-13-Trp RDS mutation or an Arg-135-Trp RHO mutation. The phenotypes of double and single heterozygotes were determined to examine the hypothesis that digenic inheritance may increase disease expression. In the family with ROM1 and RDS mutations, single heterozygotes were normal but one double heterozygote showed severe RP. Two other double heterozygotes, however, were normal by clinical and retinal function tests. In the family with ROM1 and RHO mutations, single heterozygotes with the RHO mutation all manifested RP, while a single heterozygote for the ROM1 mutation was normal. Disease severity was comparable in double heterozygotes and single heterozygotes HAVING the RHO mutation. We conclude that the Arg-16-His ROM1 gene mutation is non-pathogenic in the single heterozygous state, and there is no consistent evidence of digenic augmentation of pathogenicity in double heterozygotes carrying the Arg-16-His ROM1 mutation with either the benign Arg-13-Trp RDS mutation or the disease-causing Arg-135-Trp RHO mutation.