Sorbitol dehydrogenase (SORD) was quantitatively assayed in a family in which four out of five brothers and their father had bilateral cataracts. Three sibs (two of them with cataracts) and both their father and paternal grandfather had SORD activity of about 25% of the reference values; of the other two affected sibs one had about 50% and the other had 75%; the mother and two paternal uncles had about 75%. These results do not define a clear cataract-SORD deficiency etiopathogenic relationship, nevertheless, they strongly suggest activity polymorphism in human red cell SORD, which would be highly relevant not only to the study of cataracts but of other major complications in diabetes.
Membrane-bound and soluble forms of erythrocyte sorbitol dehydrogenase (SORD) activity are compared in normal individuals. Both isoenzymes showed similar properties. In a family with red cell SORD deficiency and congenital cataracts, Km values for sorbitol and NAD+ as well as the effect of the enzymatic deficiency on sorbitol accumulation in red cells incubated in high-glucose or high-fructose media were determined. In SORD-deficient patients, the enzymatic deficiency was observed in both crude haemolysate and SORD-M preparations with sorbitol, galactitol, xylitol or ribitol as substrates. The mutation responsible for SORD deficiency did not modify the Km for sorbitol and NAD+. Finally, SORD deficiency produced a significant increase of sorbitol accumulation in red cells incubated in high-concentration glucose media and a significant decrease when the cells were incubated in high-concentration fructose media.
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