Molecular basis for phenotypic heterogeneity in galactosaemia: prediction of clinical phenotype from genotype in Japanese patients

We identified 14 mutations in 15 Japanese subjects from 13 families with ga lactose-1-phosphate uridyltransferase (GALT) deficiency using denaturing gr adient gel electrophoresis (DGGE) and direct sequence analysis, These mutat ions accounted for 22 (96%) of 23 mutant alleles in 15 Japanese subjects, T he mutational spectrum included nine missense mutations (M142V, G179D, A199 T, R231H, W249R, N314D, B325L, R333Q, and R333W), two deletions (L275fsdelT and Q317fsdelC), a nonsense mutation (W249X), and two splicing mutations ( V85-N97fsdel38bp and IVS4nt(+)1), Ten of the 14 mutations have not been rep orted in Caucasians, Differences in frequency and spectrum of GALT mutation s suggest that the mutations may have occurred after racial divergence of C aucasians and Asians. The Duarte variant in Japanese was associated with th e N314D mutation, g.1105G > C, g.1323G > A, and g.1391G > A (SacI -) polymo rphisms, as in Caucasians. The Duarte variant may have occurred before raci al divergence, and was an ancient mutation, In vitro GALT activities of nin e missense mutations were determined by a COS cell expression system, and i ndicated between 1.3% and 35% of wild-type control. Patients with R333Q (29 % in vitro GALT activity) or A199T (35%) showed mild clinical phenotypes, i e no ovarian failure or neurological deterioration, Genotype determination is useful for predicting biochemical and clinical phenotypes in classic gal actosaemia, and can be of further help in managing patients with this disor der.