OMIM ID:
Corneal Dystrophy, Macular
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Macular corneal dystrophy is a progressive, bilateral disorder with increasing corneal cloudiness throughout life. The onset of corneal haze is variable. It can be seen in infancy but usually becomes apparent in the second or later decades of life. Visual impairment can be severe, especially by mid-life. The stroma, Descemet membrane, and endothelium are involved as keratocytes and endothelial cells accumulate intracytoplasmic vacuoles of glycosaminoglycans. Corneal thickness is reduced, presumably due to abnormally dense packing of collagen fibrils in the stroma. The epithelium does not seem to be involved.
Based on immunohistochemical profiles of inclusions, as well as phenotypic differences, attempts have been made to distinguish at least three types of macular dystrophy, I, IA, and II. This may not be justified as the same gene is involved, and especially since several types have been described within the same inbred family. Most likely these are variations in the phenotypic expression of the same gene, a feature of many genetic disorders.
Systemic Features
No extraocular abnormalities have been associated with this disorder. However, variations in serum levels of antigenic keratin sulfate have been found.
Genetics
Inheritance
Homozygous mutations in the CHST6 gene (16q22) are responsible for this autosomal recessive corneal dystrophy. More than 100 mutations have been found.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.