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Rom-1 and peripherin are related membrane proteins of the photoreceptor outer segments. Both proteins are located at the rims of the photoreceptor disks, where they may act jointly in disk biogenesis. Mutations in the gene (RDS) encoding peripherin cause autosomal dominant retinitis pigmentosa, autosomal dominant punctata albescens and butterfly macular degeneration in man, and retinal degeneration slow in mice. To facilitate ROM1 mutation and linkage analysis in inherited retinal diseases, we cloned and characterized the human and murine ROM1 genes. In both species, the ROM1 coding region is contained within approximately 1.8 kb of genomic DNA and is interrupted by only two introns. The structures of the ROM1 and RDS genes are similar, with perfect conservation of the intron splice sites. Putative transcription regulatory regions of the ROM1 locus, 5' to an apparent transcription start site, were identified by cloning the mouse Rom-1 gene and comparing the sequence to the human homologue. Alignment of the human and murine rom-1 predicted protein sequences with the peripherin polypeptides of four species reveals a high degree of conservation (47% overall identity between the six proteins) in the central hydrophilic domain of the two family members. Despite this conservation of sequence, the predicted pI's of only this region of rom-1 and peripherin differ substantially, being 5.2 and 8.2, respectively. The charge difference in this region may mediate the non-covalent association of these two proteins in vivo. The conserved genomic structure and sequence of ROM1 and RDS indicates that these genes evolved from a common ancestor by duplication event.

Long range physical mapping within the p21 region of the X chromosome identified a CpG rich island approximately 180 kb centromeric to the chronic granulomatous disease (CGD) locus. The segments adjacent to the CpG island hybridized to discrete bands in DNAs of several species and when used to screen retinal cDNA libraries led to the identification of cDNAs that detected a mRNA of 2.1 kb in many tissues. Molecular characterization of corresponding genomic clones of this novel human gene confirmed the origin of the cDNA clones and indicated a genomic structure with five exons spanning a total of 9 kb. The complete cDNA sequence revealed that this gene contained a putative open reading frame of 116 amino acids with a 3' untranslated region of 1.74 kb. The amino acid sequence shows a high degree of similarity to the predicted product of the tctex-1 gene of the mouse t complex. As linkage studies and patients with deletions have implicated the Xp21 region as containing the retinitis pigmentosa defect (RP3), the gene was assessed as a candidate disease gene in RP3 families. A single base pair polymorphism was identified within the coding region but no disease associated changes were found by single strand conformational polymorphism and sequencing analysis of amplified exons of 20 RP patients. Analysis of a dinucleotide repeat polymorphism within this gene in families affected with RP3 suggested refinement of the RP3 region.

Central core disease (CCD) is a morphologically distinct, autosomal dominant myopathy with variable clinical features. A close association with malignant hyperthermia (MH) has been identified. Since MH and CCD genes have been linked to the skeletal muscle ryanodine receptor (RYR1) gene, cDNA sequence analysis was used to search for a causal RYR1 mutation in a CCD individual. The only amino acid substitution found was an Arg2434His mutation, resulting from the substitution of A for G7301. This mutation was linked to CCD with a lod score of 4.8 at a recombinant fraction of 0.0 in 16 informative meioses in a 130 member family, suggesting a causal relationship to CCD.