Fish-Eye Disease
Fish-eye disease is a rare genetic condition characterized by the gradual clouding of the corneas, which can lead to severe visual impairment.
Overview & Symptoms
Fish-eye disease, also known as partial LCAT deficiency, is a disorder that causes the clear front surface of the eyes (the corneas) to gradually become cloudy. This cloudiness typically first appears during adolescence or early adulthood.
The clouding is caused by the accumulation of small, grayish dots of cholesterol (opacities) distributed across the corneas. Cholesterol is a waxy, fat-like substance produced by the body and obtained through animal-based foods. While essential for many bodily functions, excessive amounts can be harmful. As fish-eye disease progresses, the corneal cloudiness worsens, which can eventually result in severely impaired vision.
Frequency
Fish-eye disease is an exceptionally rare disorder, with approximately 30 cases reported in medical literature.
Causes & Genetic Factors
The condition is caused by mutations in the LCAT gene, which provides instructions for producing the enzyme lecithin-cholesterol acyltransferase (LCAT).
The LCAT enzyme is responsible for removing cholesterol from the blood and tissues by helping it attach to lipoproteins, which transport it to the liver for redistribution or removal. The enzyme performs two primary functions:
- Alpha-LCAT activity: Helps attach cholesterol to high-density lipoprotein (HDL).
- Beta-LCAT activity: Helps attach cholesterol to very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL).
Mutations causing fish-eye disease specifically impair alpha-LCAT activity, reducing the enzyme's ability to attach cholesterol to HDL. This impairment leads to the formation of cholesterol-containing opacities in the corneas. It is currently unknown why these cholesterol deposits selectively affect only the corneas in this disorder.
In contrast, mutations that impair both alpha- and beta-LCAT activity result in a related, more systemic disorder called complete LCAT deficiency, which involves corneal opacities alongside symptoms affecting other parts of the body.
Inheritance Pattern
Fish-eye disease is inherited in an autosomal recessive pattern. This means that an affected individual must inherit two mutated copies of the LCAT gene (one from each parent) to develop the condition. Parents of an individual with an autosomal recessive disorder typically carry one copy of the mutated gene but do not experience signs or symptoms of the disease.
Other Names for This Condition
- Alpha-LCAT deficiency
- Alpha-lecithin:cholesterol acyltransferase deficiency
- Dyslipoproteinemic corneal dystrophy
- FED
- LCATA deficiency
- Partial LCAT deficiency