Retinal histopathology of an XLRP carrier with a mutation in the RPGR exon ORF15.

X-linked retinitis pigmentosa comprises the severe forms of RP, with early onset of night blindness, rapid constriction of visual fields and eventual loss of central acuity. Of the five distinct XLRP loci identified on the X chromosome, mutations have been found only in the RP2 and RPGR genes. Of these, mutations in RPGR are more common, particularly in a mutational hot spot that was identified in the newly discovered exon ORF15. We report on an extended family with a microdeletion in RPGR exon ORF15 and the retinal histopathology of a female carrier of this mutation. We found a 1bp deletion at position 632 in exon ORF15 in affected members of family XLRP-319. This mutation alters the reading frame of the predicted RPGR protein, resulting in a premature stop codon. The mutation segregated with disease in three generations of the family and was associated with severe early onset retinal disease in affected men. The retina from a 75 year old carrier female donor had slight photoreceptor loss in the less diseased areas. More severe atrophy with retinal pigment epithelium (RPE) migration was present in areas of the mid- and far periphery. By immunocytochemistry, loss of rhodopsin labelling in rods was found in the areas of focal atrophy and loss of uniform cone spacing was apparent even in well preserved regions. Small multifocal areas of outer retinal degeneration were present in the better preserved regions of the eye. In these foci, rod and cone loss did not coincide. The dissociation of rod and cone degeneration in areas of focal disease is consistent with random X-inactivation early in embryonic development and the occurrence of distinct patterns of radial (rod) and tangential (cone) dispersion during clonal expansion early in photoreceptor differentiation.

Identification and subcellular localization of the RP1 protein in human and mouse photoreceptors.

PURPOSE: Mutations in the RP1 gene account for 6% to 10% of autosomal dominant retinitis pigmentosa (adRP). Previous studies have shown that the RP1 gene is expressed specifically in photoreceptor cells. So far, little is known about the RP1 protein or how mutations in RP1 lead to photoreceptor cell death. The goal of this study was to identify the RP1 protein and investigate its location in photoreceptor cells. METHODS: A combination of RT-PCR and rapid amplification of cDNA ends (RACE) was used to isolate the full-length mouse Rp1 cDNA. Antibodies against different regions of the predicted mouse Rp1 protein were generated. Western blot analyses were used to identify the RP1/Rp1 proteins. The subcellular location of RP1 in human and mouse retinas was determined by immunostaining retinal sections. RESULTS: The full-length mouse Rp1 cDNA is 6944 bp, encoding a predicted protein of 2095 amino acids. Rp1 was found to be a soluble protein of approximately 240 kDa, consistent with predictions based on the cDNA sequence. Immunofluorescence analyses revealed that both the human RP1 and mouse Rp1 proteins are specifically localized in the connecting cilia of rod and cone photoreceptors. CONCLUSIONS: The presence of RP1/Rp1 in connecting cilia suggests that it may participate in transport of proteins between the inner and outer segments of photoreceptors or in maintenance of cilial structure. This study forms the basis for further investigation of the function of RP1 in retina and the mechanism by which mutations in RP1 lead to photoreceptor cell death.