The Gene Causing Inherited Cataracts In Sheep Maps To Chromosome 6

Abstract

Purpose: : To map the gene for an inherited cataract in sheep. Previous research had shown that this cataract is inherited as an autosomal dominant trait. About 40% of the lambs resulting from mating rams with cataracts with normal ewes develop bilateral opacities in the cortex of the lens within 2 months and these develop to mature cataracts over the next six to eight months

Methods: : A ram with cataracts was mated with unrelated normal ewes. The eyes of the resulting lambs were inspected at two months of age and cataract formation was scored using slit lamp microscopy. DNA was extracted from the pedigree of this ram and 19 of his lambs with cataracts and 22 of his lambs with normal eyes. The DNA was screened for informative markers at about 20 centimorgan spacing using microsatellite markers. A total of 149 markers were screened. The results were analysed using the CRIMAP genetic linkage program.

Results: : Several markers on chromosome OAR6 showed linkage with the cataract phenotype with three showing LOD scores of 3.05, 3.77 and 4.24. When the known order (http://rubens.its.unimelb.edu.au/∼jillm/jill.htm version 4.4) of the 7 markers loci was used the cataract gene was shown to have a most likely position between 112 and 136cM from the centromere on chromosome 6.

Conclusions: : The gene causing ovine heritable cataract has been localized to chromosome 6 on the sheep genome. This region is syntenic with chromosome 4 in humans and chromosome 6 in cattle. Mapping is continuing to more precisely locate the gene and determine possible mechanisms for cataract formation.

Keywords: cataract • gene mapping • genetics