Congenital progressive polymorphic cataract caused by a mutation in the major intrinsic protein of the lens, MIP (AQP0)

Background-Congenital cataract, when inherited as an isolated abnormality, is phenotypically and genetically heterogeneous. Although there is no agree d nomenclature for the patterns of cataract observed, a recent study identi fied eight readily identifiable phenotypes. Methods-The Moorfields Eye Hospital genetic eye clinic database was used to identify a four generation family with isolated autosomal dominant congeni tal cataracts. All individuals (affected and unaffected) underwent a full o phthalmic assessment. Results-The results of the molecular linkage study identifying a missense m utation in the gene encoding the major intrinsic protein of the lens (MIP) have been published elsewhere. Affected individuals had bilateral discrete progressive punctate lens opacities limited to mid and peripheral lamellae with additional asymmetric polar opacification. One young female had predom inantly cortical cataract and another had serpiginous nuclear opacities. Conclusions-This phenotype has not been recorded in human families before a nd has been termed polymorphic. The pattern of opacification appears to ref lect the distribution of MIP in the lens. Furthermore, this is the first cl ear evidence of allelic heterogeneity in this condition following the ident ification of a family with lamellar cataracts who have a different mutation within the MIP gene.