BLACK-CHILDREN DEFICIENT IN GALACTOSE 1-PHOSPHATE URIDYLTRANSFERASE -CORRELATION OF ACTIVITY, AND IMMUNOREACTIVE PROTEIN IN ERYTHROCYTES AND LEUKOCYTES

A recent study found a high prevalence of a missense mutation (S135L) in the gene for galactose 1-phosphate uridyltransferase (GALT) in blac k children with galactosemia (J Pediatr 1996;128:89-95). In the presen t study, GALT activity and GALT protein content were measured in eryth rocytes and leukocytes of eight black and seven white galactosemic (GA LT-deficient) children, for correlation with the presence of the S135L and Q188R (highly prevalent in white galactosemic children) missense mutations, This S135L mutation was found in 9 of 16 alleles of black c hildren but not in white children; the Q188R mutation was found in 10 of 14 alleles examined in white galactosemic children and in 4 of 16 a lleles in black galactosemic children, The GALT activity was near zero in the erythrocytes of white and black galactosemic children (0.26 +/ - 0.28 vs 0.33 +/- 0.25 mu mol/hr per gram of hemoglobin, respectively ; p = 0.61) (normal 17 to 26 umol/hr per gram), and no correlation of erythrocyte activity with genotype was observed. The GALT activity was higher in the leukocytes of black galactosemic children compared with white children (5 +/- 6 vs 1 +/- 2 mu mol/hr per gram, respectively) (normal 172 to 374 mu mol/hr per gram), but the difference was not sta tistically significant (p = 0.11). Analysis by genotype revealed that the two S135L homozygotes had much more leukocyte activity (9 and 17 m u mol/hr per gram) than Q188R homozygotes or than ail non-S135L alleli c genotypes. Compound heterozygotes (S135L/G) had intermediate activit y. The GALT protein was not detectable by Western blot in the erythroc ytes of either white or black galactosemic children, as determined by antibodies specific for both C- and N-terminal sequences. The GALT pro tein was undetectable in the leukocytes of white galactosemic children , but leukocytes from black galactosemic children with the S135L mutat ion contained reduced but readily detectable GALT protein. Erythrocyte galactose 1-phosphate levels were significantly lower in galactosemic children with an S135L mutant allele (1.1 +/- 0.2 gm/dl) compared wit h children who had other mutations (3.1 +/- 0.9 mg/dl; p = 0.0001). Th e correlation of protein content data with activity levels in the bloo d cells suggests that the S135L missense mutation affects the stabilit y of GALT protein to produce a deficiency state.