The Identification and Characterization of the Gene Responsible for Autosomal Recessive Congenital Hereditary Endothelial Dystrophy (CHED2) on 20p13

Abstract

Purpose: : CHED is a bilateral disorder characterized by a loss of endothelial cells that result in an oedematous cornea with opacification ranging from a diffuse haze to a ground glass milk appearance that often necessitates keratoplasty. CHED can be inherited either as an autosomal dominant (CHED1) or as a recessive (CHED2) disease. The locus for CHED2 was previously localized to an 8 cM interval on chromosome 20p13. We used a novel consanguineous, autosomal recessive CHED family from Myanmar to refine the disease interval and to identify and characterize the gene for CHED2.

Methods: : This family was subjected to linkage analysis with 21 short tandem repeat (STR) markers from the CHED2 region on chromosome 20p13. Mutational analysis of positional candidate genes was by bi–directional sequencing.

Results: : Segregation analysis of STR markers in informative recombinants in this family refined the CHED2 locus to a ∼ 2.5Mb interval containing at least 30 genes. A positional candidate gene approach was adopted to identify the gene responsible for CHED2. A homozygous sequence variation resulting in the amino acid substitution of a highly conserved residue was found to co–segregate with the disease. In addition, mutational analysis in 7 other CHED2 families from India and Pakistan revealed 4 novel mutations that co–segregated with the disease in all cases. None of these variants were identified in over 100 ethnically matched control individuals. Furthermore all mutation sites showed high interspecies conservation.

Conclusions: : In total 8 families with missense and nonsense mutations have been shown to cause autosomal recessive CHED. Further functional characterization of these mutations are currently being undertaken to understand how these mutations may impinge on the proliferation and development of the endothelial cells and thus give rise to the histopathological features of CHED.

Keywords: cornea: basic science • cornea: endothelium • gene mapping