Cf Inglehearn

Autosomal dominant retinitis pigmentosa: four new mutations in rhodopsin, one of them in the retinal attachment site

Several mutations in the rhodopsin gene in patients affected by autosomal dominant retinitis pigmentosa (ADRP) have recently been described. We report four new rhodopsin mutations in ADRP families, initially identified as hetero-duplexed PCR fragments on hydrolink gels. One is an in-frame 12-bp deletion of codons 68 to 71. The other three are point mutations involving codons 190, 211, and 296. Each alters the amino acid encoded. The codon 190 mutation has been detected in 2 from a panel of 34 ADRP families, while the remaining mutations were seen in single families. This suggests that, consistent with a dominant condition, no single mutation will account for a large fraction of ADRP cases. The base substitution in codon 296 alters the lysine residue that functions as the attachment site for 11-cis-retinal, mutating it to glutamic acid. This mutation occurs in a family with an unusually severe phenotype, resulting in early onset of disease and cataracts in the third or fourth decade of life. This result demonstrates a correlation between the location of the mutation and the severity of phenotype in rhodopsin RP.

Abnormal dark adaptation kinetics in autosomal dominant sector retinitis pigmentosa due to rod opsin mutation.

The time course of dark adaptation was measured in 10 subjects from three families with autosomal dominant sector retinitis pigmentosa (RP) due to mutations in the first exon of the rod opsin gene. In each subject cone adaptation and the early part of the recovery of rod sensitivity followed the normal time course, but the later phase of rod adaptation was markedly prolonged. The recovery of rod sensitivity is much slower than that reported in any other outer retinal dystrophy. Using a model based upon primate data of rod outer segment length and turnover, we have calculated that the delayed phase of the recovery of rod sensitivity in the RP patients tested following strong light adaptation could be due in part to formation of new disc membrane with its normal concentration of rhodopsin rather than in situ regeneration of photopigment.

Autosomal dominant retinitis pigmentosa with apparent incomplete penetrance: a clinical, electrophysiological, psychophysical, and molecular genetic study.

Twenty five symptomatic individuals and six asymptomatic obligate gene carriers from four families with autosomal dominant retinitis pigmentosa (adRP) showing apparent incomplete penetrance have been studied. Symptomatic individuals from three families showed early onset of night blindness, non-recordable rod electroretinograms, and marked elevation of both rod and cone thresholds in all subjects tested. In the fourth family, there was more variation in the age of onset of night blindness and some symptomatic individuals showed well preserved rod and cone function in some retinal areas. All asymptomatic individuals tested had evidence of mild abnormalities of rod and cone function, indicating that these families show marked variation in expressivity rather than true non-penetrance of the adRP gene. No mutations of the rhodopsin or RDS genes were found in these families and the precise genetic mutation(s) remain to be identified.

Bimodal expressivity in dominant retinitis pigmentosa genetically linked to chromosome 19q.

A clinical, psychophysical, and electrophysiologic study was undertaken of two autosomal dominant retinitis pigmentosa pedigrees with a genetic mutation assigned to chromosome 19q by linkage analysis. Members with the abnormal haplotype were either symptomatic with adolescent onset nyctalopia, restricted visual fields, and non-detectable electroretinographic responses by 30 years of age, or asymptomatic with normal fundus appearance and minimal or no psychophysical or electroretinographic abnormalities. There was no correlation in the severity in parents and their offspring. Pedigree analysis suggested that although the offspring of parents with the genetic mutation were at 50% risk of having the genetic defect, the risk of being symptomatic during a working lifetime was only 31%. Such bimodal phenotypic expressivity in these particular pedigrees may be explained by a second, allelic genetic influence and may be a phenomenon unique to this genetic locus. Genetic counselling in families expressing this phenotype can only be based on haplotype analysis since clinical investigations, even in the most elderly, would not preclude the presence of the mutant gene.

Autosomal dominant retinitis pigmentosa mapping to chromosome 7p exhibits variable expression

The genetic locus causing autosomal dominant retinitis pigmentosa (adRP) has recently been mapped in a large English family to chromosome 7p. Eight affected members of this family were studied electrophysiologically and psychophysically with dark adapted static threshold perimetry and dark adaptometry. The phenotypes observed fell into three categories: minimally affected with no symptoms, and normal (or near normal) electrophysiology and psychophysics; moderately affected with mild symptoms, abnormal electroretinograms, and equal loss of rod and cone function in affected areas of the retina; and severely affected with extinguished electroretinograms and barely detectable dark adapted static threshold sensitivities. The mutation in the gene on 7p causing adRP in this family causes regional retinal dysfunction with greatly variable expressivity ranging from normal to profoundly abnormal in a manner not explained by age.

Ocular manifestations in autosomal dominant retinitis pigmentosa with a Lys-296-Glu rhodopsin mutation at the retinal binding site.

A lysine to glutamic acid substitution at codon 296 in the rhodopsin gene has been reported in a family with autosomal dominant retinitis pigmentosa. This mutation is of particular functional interest as this lysine molecule is the binding site of 11-cis-retinal. The clinical features of a family with this mutation have not been reported previously. We examined 14 patients with autosomal dominant retinitis pigmentosa and a lysine-296-glutamic acid rhodopsin mutation. Four had detailed psychophysical and electrophysiological testing. Most affected subjects had severe disease with poor night vision from early life, and marked reduction of visual acuity and visual field by their early forties. Psychophysical testing showed no demonstrable rod function and severely reduced cone function in all patients tested.

Exclusion of chromosome 6 and 8 locations in nonrhodopsin autosomal dominant retinitis pigmentosa families: further locus heterogeneity in adRP

Genetic studies have revealed that 25 to 30% of autosomal dominant retinitis pigmentosa (adRP) families have mutations in the rhodopsin gene, while the remainder do not. More recently linkage data and mutation detection have demonstrated two further loci implicated in adRP, at an as yet unidentified gene on chromosome 8p and at the human gene homologue of the mouse Rds (Retinal Degeneration Slow) gene on chromosome 6p. We have previously reported exclusion of adRP from the rhodopsin locus on 3q in two large adRP families. We now report exclusion data for both families, on chromosomes 6 and 8, demonstrating that the adRP phenotype results from mutations in at least four locations.

Localization of the aquaporin 1 (AQP1) gene within a YAC contig containing the polymorphic markers D7S632 and D7S526

The aquaporin protein acts as a water selective, transmembrane channel. It is expressed in a wide range of tissues and organs and is especially abundant in the anterior segment of the eye. Studies have shown that there is only a single AQP1 gene locus, which has been localized by in situ hybridization to chromosome 7p14. A study by Deen et al. failed to identify any RFLP at the AQP1 locus. A poly(CA) sequence 400 bp upstream of the transcription start site also proved to be nonpolymorphic. The same authors identified six other sequence-tagged sites from a single cosmid containing the entire AQP1 gene. These all contained repeat motifs, but none was investigated for possible size variation at that time. 7 refs., 1 fig.

Linkage of internal minisatellite loci on chromosome 1 and exclusion of autosomal dominant retinitis pigmentosa proximal to rhesus.

We report the exclusion of a locus for autosomal dominant retinitis pigmentosa proximal to the rhesus locus in a single large pedigree. In addition, a previously unreported linkage is described between two chromosome 1 markers, which confirms that a highly variable minisatellite locus is placed internally on chromosome 1.

FREQUENCIES OF DIFFERENT FORMS OF AUTOSOMAL-DOMINANT RETINITIS-PIGMENTOSA AND A NEW LOCUS FOR ADRP

m Seven loci for dominant retinitis pigmentoeehave been described in the literature. These include the Rhodopsin and Rdslperipherin genee. and anonymous loci identtfted only by linkage on 7p, 7q. aq, 17p and 19q. We wishedto estimatethe frequendesof the anonymous loci, and determinewhether any adRP loci remained to be found. &@g& DNAe were colleded from twenty ftve adRP families. These were tested by linkage analyeis and mutetiin screening to determine the origin of the phenotype in each family. j&t& Of the twenty five families, the diiease in twelve wes found to be rhcdwein RP either bv linkaae analwie or by mutation detection. A further three map& the 19q adRP &us. one to {he 7p l&us. and one to the 17p locus. Three other familiee gave tentative evidence of linkege,hvo to 19q and one to sq. Four families show crcssovere at all the known loci. Finally in one large family we discovered a new locus. on chromosome 17q between markers D17SBo9 and Dl7S942. Multipoint enalysie in this fern@ gave e maximum led sccfe of 8.24 in this interval. Concluelone In this sample, Rho-RP accounted for approximately50% of adRP while the 19q lccus(RP11) accented for around 20%. All other loci ere rare. Approximately 15% of families map to an unknown locus or loci, proving that adRP is caused by mutations in at least nine dinerent genes.