Human L-xylulose reductase variation: family and population studies.

Only one of the two main L-xylulose reductases present in human tissue is deficient in individuals with essential pentosuria (Lane, 1985). The isozyme which is affected by the pentosuria mutation occurs as mitochondrial and cytosolic forms in normal individuals, whereas the other isozyme (which is not affected by the mutation) occurs only in the cytosol. A new assay of red cell L-xylulose reductase activity has facilitated the identification of carriers of the essential pentosuria allele at both family and population levels. Reinvestigation of a Lebanese family in which pentosuria has previously been thought to be dominantly inherited reveals that the condition is recessively inherited in this family as well. A minimum estimate of the frequency of the pentosuria allele in an Ashkenazi-Jewish population, calculated from the apparent heterozygote frequency, is 0.0127. The likelihood of the Ashkenazi and Lebanese pentosuria alleles being the same is discussed.