OMIM ID:
Corneal Dystrophy, Schnyder
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Schnyder corneal dystrophy has its onset early in life as a haziness of the central cornea with some peripheral extension. The stroma gradually becomes more hazy and eventually in about 50% of patients yellow-white crystalline deposits can be seen in an annular pattern in the Bowman layer and the adjacent stroma just beneath. The remaining layers of the cornea are not involved. The needle-shaped crystals are often birefringent and composed of cholesterol and phospholipids. There is considerable variation in the progression of disease and in the symmetry of disease in the two eyes. Visual acuity may be relatively good in young people but older patients with denser central opacification eventually require corneal transplantation for better vision.
Systemic Features
Some patients have hypercholesterolemia and hyperlipidemia. Skin fibroblast cultures in one patient have shown cytoplasmic deposits consistent with unesterified cholesterol but another study failed to find such deposits in skin or conjunctiva. Evidence points to a metabolic disorder of lipid metabolism in the cornea but the evidence for a more generalized systemic disorder is inconclusive. Genu valgum has been reported in some patients.
Genetics
Inheritance
Schnyder crystalline dystrophy of the cornea results from a mutation in the UBIAD1 gene located on chromosome 1 (1p36.3). Multiple mutations have been identified. It is inherited in an autosomal dominant pattern.
Pedigree
Autosomal dominant
Autosomal dominant disorders require only one mutation for the disease to be expressed. Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease. It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).
Autosomal dominant inheritance leads to a vertical pattern of transmission