Phenotype of retinitis pigmentosa associated with the Ser50Thr mutation in the NRL gene.

BACKGROUND: We previously reported an Ser50Thr mutation in the NRL gene as a cause of autosomal dominant retinitis pigmentosa.
OBJECTIVE: To determine the characteristic features of the autosomal dominant retinitis pigmentosa phenotype associated with the NRL Ser50Thr mutation in affected individuals from 4 related families.
METHODS: Clinical records were available for 21 affected individuals; 7 underwent more extensive electrophysiologic and psychophysical testing.
RESULTS: Night blindness was the first symptom to manifest, with onset between birth and age 16 years. Difficulty with peripheral vision was experienced between 20 and 37 years of age. Visual acuity was well preserved in younger individuals, but those older than 30 years frequently had substantial visual loss (6/36 or worse) associated with macular atrophy. Electrophysiologic testing revealed a nondetectable scotopic electroretinogram with relative preservation of the photopic electroretinogram and pattern electroretinography in the 3 youngest patients tested (aged 15-18 years). In older individuals, all components of the electroretinogram were nondetectable. Dark-adapted visual fields in younger individuals were greatly impaired, but their photopic fields remained relatively well preserved. Older patients had photopic fields limited to just a few degrees. Distinctive peripapillary chorioretinal atrophy seems to develop as the disorder progresses.
CONCLUSIONS: The NRL Ser50Thr mutation is associated with selective loss of scotopic function before age 20 years. With time, however, the photopic system becomes affected, leading to loss of the photopic visual field and of visual acuity.