Genetic fine localization of the arrestin (S-antigen) gene 4 cM distal from D2S172

A new autosomal recessive retinitis pigmentosa locus maps on chromosome 2q31-q33

Autosomal recessive retinitis pigmentosa (ARRP) is a genetically heterogeneous disease. To date, mutations in four members of the phototransduction cascade have been implicated in ARRP. Additionally, linkage of the disease to three loci on 1p, 1q, and 6p has been described. However, the majority of cases are still uncharacterised. We have performed linkage analysis in a large nuclear ARRP family with five affected sibs. After exclusion of several regions of the genome known to contain loci for retinal dystrophies, a genomic search for linkage to ARRP was undertaken. Positive lod scores were obtained with markers on 2q31-q33 (Zmax at theta = 0.00 of 4.03, 4.12, and 4.12 at D2S364, D2S118, and D2S389, respectively) defining an interval of about 7 cM for this new ARRP locus, between D2S148 and D2S161. Forty-four out of 47 additional ARRP families, tested with markers on 2q32, failed to show linkage, providing evidence of further genetic heterogeneity.

Identification of genes causing photoreceptor degenerations leading to blindness

At least 15 genes with defects responsible for various forms of inherited retinal disease involving photoreceptor loss have been identified over the past eight years. Several of the genes were first considered as candidates for study because of their involvement in murine retinal disease, others because of their chromosomal loci. In two cases, novel genes were uncovered by positional cloning. Based on reports of disease loci for which no gene has yet been found, more than twice as many genes remain to be identified in this genetically heterogeneous group of diseases.

A homozygous 1-base pair deletion in the arrestin gene is a frequent cause of Oguchi disease in Japanese

Oguchi disease is a rare autosomal recessive form of congenital stationary night blindness with all other visual functions, including visual acuity, visual field, and colour vision being usually normal. A typical clinical feature of the disorder is a golden or gray-white discolouration of the fundus which disappears in the dark-adapted state and reappears shortly after the onset of light ('Mizuo phenomenon'; Fig. 1). The course of dark adaptation of rod photoreceptors is extremely retarded in Oguchi disease while that of cones appears to proceed normally. The locus for Oguchi disease was recently mapped between D2S172 and D2S345 on distal chromosome 2q by linkage analysis. Interestingly, the gene for arrestin, an intrinsic rod photoreceptor protein implicated in the recovery phase of light transduction, also maps to this region of chromosome 2q (refs 6, 7). Here we report that in five out of six unrelated Japanese patients with Oguchi disease, we have identified a homozygous deletion of nucleotide 1147 (1147delA) in codon 309 of the arrestin gene, predicting a shift in the reading frame and a premature termination of translation which may result in 'functional null alleles.'

Oguchi disease: suggestion of linkage to markers on chromosome 2q

Oguchi disease is a rare autosomal recessive form of congenital stationary night blindness. The condition is associated with fundus discolouration and abnormally slow dark adaptation. Earlier studies suggested that the 48 kD protein S antigen may be involved in the recovery phase of light transduction. Previous cytogenetic and linkage studies have localised the S antigen gene (SAG) to chromosome 2q37.1. In the present study markers which map to distal chromosome 2q were typed in an inbred Oguchi pedigree. The segregation data obtained suggested that the affected subjects are homozygous by descent for a region between D2S172 and D2S345. An intragenic SAG polymorphism was homozygous in all affected people and a recombination event suggested that SAG maps proximal to D2S345. Collectively, these findings support the hypothesis that a defect in S antigen may be responsible for Oguchi disease.