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 agreed nomenclature for the patterns of cataract observed, a recent study identified 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 congenital cataracts. All individuals (affected and unaffected) underwent a full ophthalmic assessment. RESULTS The results of the molecular linkage study identifying a missense mutation 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 predominantly cortical cataract and another had serpiginous nuclear opacities. CONCLUSIONS This phenotype has not been recorded in human families before and has been termed polymorphic. The pattern of opacification appears to reflect the distribution of MIP in the lens. Furthermore, this is the first clear evidence of allelic heterogeneity in this condition following the identification of a family with lamellar cataracts who have a different mutation within the MIP gene.