This is one of numerous hereditary enzymatic disorders involving fat (lipid) metabolism. A defect in a gene called LCAT (lecithin:cholesterol acyltransferase) leads to disorders known as Norum disease and another mutation causes fish-eye disease. It was first reported in Norway in 1967.
Both disorders have prominent cholesterol deposits in the cornea resulting in vision difficulties. Norum disease in addition leads to anemia and kidney failure. The corneal opacities are progressive with onset in the first two decades of life. Contrary to expectations, high levels of cholesterol and triglycerides together with reduced quantities of HDL (the ‘good’ cholesterol) do not lead to an increased risk of atherosclerotic heart disease.
The LCAT gene is located on chromosome 16 and two mutated copies, one contributed by each parent, are necessary to cause these disorders (autosomal recessive inheritance). The family pattern is a horizontal pattern and if both parents carry the mutation in a single dose, they are clinically normal but have a 25% chance of having an affected child from each pregnancy.
Reduced vision resulting from clouding of the cornea can be diagnosed by your eye doctor but biochemical analysis of the blood is necessary for determination of the specific type of LCAT deficiency. Anemia and protein in the urine may also suggest the diagnosis but blood analysis is again necessary for confirmation.
Corneal transplants and/or kidney transplantation can be helpful treatments. No effective dietary treatment has been reported.