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 characterized by hypergalactosemia and cataract formation. Through mass screening of newborn infants, we identified a novel and prevalent GALK variant (designated here as the "Osaka" variant) associated with an A198V mutation in three infants with mild GALK deficiency. GALK activity and the amount of immunoreactive protein in the mutant were both 20% of normal construct in expression analysis. The K(m) values for galactose and ATP-Mg(2+) in erythrocytes with homozygous A198V were similar to those of the healthy adult control subjects. 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 frequency (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.