Definition: Two forms of CHED causing bilateral congenital corneal edema are described: autosomal recessive and autosomal dominant. The more common autosomal recessive form is present at birth, remains stable, and is accompanied by nystagmus.
Incidence/Prevalence: Etiology: Originally, 7 different mutations have been identified in 10 families within the SLC4A11 gene in patients with AR CHED. The mutations involve a gene that encodes a membrane-bound sodium-borate cotransporter, and cause loss of function of the protein either by blocking its membrane targeting or perhaps nonsense-mediated decay. (1) As of 11/25/2007 30 different mutations have been identified in the SLC4A11 gene.
Clinical Findings: Clinically CHED shows a diffuse ground glass opacity of the cornea that is bilateral and progressive. There are 2 modes of inheritance that are reported. In the autosomal recessive form, edema appears within the neonatal period (sometimes at birth) and is associated with nystagmus. In the autosomal dominant form the cornea is clear at birth and the clouding progresses slowly usually at 1-2 years of age; nystagmus does not develop. There are no guttata here, distinguishing it from Fuch's dystrophy.
Both forms have a similar clinical appearance to the cornea. In the clinical image graciously provided by Dr. Aldave, the cornea appears bluish white, and the slit beam shows that its thickness is two to three times normal. The cornea has a ground-glass appearance.
Histopathology: Congenital Hereditary Endothelial Dystrophy (CHED) is characterized by a markedly thickened stroma and Descemet's membrane (especially the posterior non-banded portion) with endothelial attenuation and vacuolization in a child.
The two forms appear similar histologically. In the PAS stained image above, hydropic changes are seen in the epithelium (arrow 1), Bowman's layer is destroyed centrally (arrow 2) and there is stromal scarring (number 3), presumably secondary to the chronic nature of the corneal edema (loss of artifactual spaces in the stroma (number 3)). Descemet’s membrane does not contain guttae (arrow 4). The endothelium is markedly vacuolated (arrow 5). Interfibrillar granular material has been reported.
Treatment: includes 5% sodium chloride drops, in attempt to reduce the corneal swelling, or corneal transplantation, may be considered.
References: Vithana EN et al, Nature Genetics 2006 38, 755 - 757.
