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Variable expressivity in X-linked congenital stationary night blindness
W G Pearce1, M Reedyk, S G Coupland
1Department of Ophthamology, University of Alberta, Edmonton.
Canadian Journal of Ophthalmology. Journal Canadien D'Ophtalmologie
|February 1, 1990
Summary
X-linked congenital stationary night blindness (CSNB) presents with varied symptoms, often missing key features in patients. This study suggests a single gene mutation causes CSNB, with significant differences in how it affects individuals.
Area of Science:
- Ophthalmology
- Genetics
- Human Physiology
Background:
- X-linked congenital stationary night blindness (CSNB) is a genetic disorder characterized by impaired night vision, nystagmus, and myopia.
- Previous research suggested potential genetic heterogeneity due to differing family presentations, possibly involving multiple X-chromosome loci or alleles.
Purpose of the Study:
- To investigate the clinical and visual function variability in X-linked CSNB.
- To determine if observed discrepancies in CSNB presentation are due to genetic heterogeneity or variable expressivity of a single genetic cause.
Main Methods:
- Clinical assessment and visual function testing of 42 affected individuals from 10 families and one adopted person.
- Analysis of clinical features, visual acuity, refractive error, and rod segment elevation.
Main Results:
- A significant proportion (75%) of patients lacked at least one cardinal feature of CSNB.
- Wide variations in visual acuity (20/30 to 20/400), refractive error (+1.50 to -22.50 D), and rod function (1.5 to 3.0 log units) were observed both between and within families.
- The disorder is under-recognized in clinical practice.
Conclusions:
- The findings support the hypothesis of a single causative allele for X-linked CSNB.
- The wide range of clinical and functional manifestations indicates significant variable expressivity of this single genetic defect.