Phenotype of chromosome 8q-linked autosomal dominant retinitis pigmentosa
Purpose. To characterize the disease expression of the autosomal dominant retinitis pigmentosa (adRF) linked to chromosome 8q. Methods. A multi-generation adRP family showed linkage between the disease locus and chromosome 8q markers; rhodopsin and peripherin/RDS gene mutations were excluded. A subset of patients were examined clinically, and with rod and cone perimetry, dark adaptometry and electroretinograms (ERGs). Rod and cone photoresponses were fitted by a model of phototransduction, and amplitude and timing of postreceptoral components quantified. Results. The disease can be initially sectoral/altitudinal, but later involves the entire midperiphery. Visual acuity is relatively well preserved but slowly declines with increased disease duration. Psychophysical and ERG data indicate that rod function is affected more than that of cones, even at early disease stages. Kinetics of rod dark adaptation are abnormal; cone adaptation is normal. Rod photoresponses show reduced maximum amplitudes and abnormal phototransduction; cone amplitudes are relatively less reduced and transduction is also abnormal. ERG evidence of disproportionate post-receptoral dysfunction for rod and cone systems is present. Conclusions. The mutant gene in this chromosome 8q-linked adRP causes an earlier and more pronounced effect on rod than cone photoreceptor function, leading to abnormalities in activation of phototransduction and the regeneration of photolyzed rhodopsin. Post-receptoral defects resemble those in other forms of RP and are presumed consequent to the receptoral disease.
Iannaccone, A; Cideciyan, AV; Sheffield, VC; Stone, EM; Jacobson, SG
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