Corneal dystrophies related to cholesterol metabolism (fish eye and Schnyder dystrophy)

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AbstractSchnyder corneal dystrophy (SCD) is a rare corneal dystrophy characterized by abnormally increased deposition of cholesterol and phospholipids in the cornea. SCD is inherited as an autosomal dominant trait with high penetrance and has been mapped to the UBIAD1 gene on chromosome 1p36.3. Diseases of systemic lipid metabolism that cause corneal opacification, such as lecithin‐ cholesterol acyltransferase (LCAT) deficiency and fish eye disease (FED), should be considered in the differential diagnosis. LCAT deficiency and FED are both entities that result from deficiency of the LCAT enzyme. LCAT deficiency is defined by deficient LCAT activity towards HDL and LDL whereas FED is defined by decreased LCAT activity against HDL only. When comparing LCAT deficiency and FED to SCD, there are numerous differences to help distinguish all 3 entities. Both LCAT deficiency and FED are inherited in an autosomal recessive manner while SCD has autosomal dominant inheritance. Systemically, SCD has a normal level of LCAT enzyme activity and normal HDL levels. Both LCAT deficiency and FED show abnormally low levels of HDL. SCD is often associated with a true arcus lipoides, unlike FED and LCAT deficiency.