Phenotypic expression of the complete type of X-linked congenital stationary night blindness in patients with different mutations in the NYX gene

Abstract

Purpose. To describe the clinical phenotype of the complete type of X-linked congenital stationary night blindness (CSNB1) with different types of mutations in the NYX gene.

Methods. The clinical and genetic data from 18 male patients with eight different mutations from two ophthalmological institutes were reviewed. The variability in refractive error, reduced visual acuity and full-field electroretinogram (ERG) recordings was examined.

Results. Parameters were quantitatively analyzed based on the classification of mutations according to their predicted effect on protein structure and function. CSNB1 patients with mutations changing structurally conserved residues (n=12) tended to have a lower degree of myopia than patients with mutations of non-conserved residues (n=6). Visual acuity loss and the 30 Hz flicker ERG recordings were similar in the two groups. Values for the b/a amplitude ratio tended to be clustered in patients carrying the same mutation. Refractive error and the b/a amplitude ratio were highly correlated between the two eyes of an individual.

Conclusions. These data suggest correlations between phenotypic expression in CSNB1 and individual genotypes as well as class types of mutations based on the extent of structural amino acid conservation. A high inter-eye correlation suggests that other genetic or environmental factors, rather than chance, play a part in determining the phenotypic diversity in CSNB1.