A genetic factor for age-related cataract: Identification and characterization of a novel galactokinase variant, "Osaka," in Asians

Galactokinase (GALK) deficiency is an autosomal recessive disorder characte rized by hypergalactosemia and cataract formation. Through mass screening o f newborn infants, we identified a novel and prevalent GALK variant (design ated here as the "Osaka" variant) associated with an A198V mutation in thre e infants with mild GALK deficiency. GALK activity and the amount of immuno reactive protein in the mutant were both 20% of normal construct in express ion analysis. The K-m values for galactose and ATP-Mg2+ in erythrocytes wit h homozygous A198V were similar to those of the healthy adult control subje cts. A population study for A198V revealed prevalences of 4.1% in Japanese and 2.8% in Koreans, lower incidence in Taiwanese and Chinese, no incidence in blacks and whites from the United States, and a significantly high freq uency (7.8%; P<.023) in Japanese individuals with bilateral cataract. This variant probably originated in Japanese and Korean ancestors and is one of the genetic factors that causes cataract in elderly individuals.