Molecular confirmation of the causes of inherited visual impairment in Northern Pakistan.

Families with inherited visual impairment were identified and examined from January 2000 to December 2005 and given a clinical diagnosis. Known genes and loci were screened for mutations or linkage at Institute of Ophthalmology and Neurosciences, University of Leeds, in order to provide molecular confirmation. Inherited retinal disease was the most common cause of inherited visual impairment in 38 of 57 families (66.6%) with Leber's congenital amaurosis, rod-cone dystrophy and cone-rod dystrophy being the most common diagnoses in 22, 8 and 3 families respectively. Anterior segment dysgenesis was diagnosed in 8 families (14%). Mutations in known genes or linkage to known loci were identified in 23 of 57 families (40%). All families had molecular confirmation of autosomal recessive inheritance or a pedigree consistent with this mode of inheritance, with evidence of first-cousin marriage. Knowledge of carrier status and genetic counseling may allow families to make an informed decision regarding marriage, and thus begin to plan a way of reducing the incidence of inherited visual impairment.