| Research Abstract |
Galactosemia (Type 1) is an autosomal recessive genetic disorder due to galactose 1-phosphate uridyltransferase (GALT) deficiency. We characterzed 13 mutations of GALT gene in 13 patients from 11 families by PCR amplification, denaturing gradient gel electorophoresis, and direct sequence analysis. We found 9 missense mutations (N97S,M142V,G179D,A199T,W249R,N314D,P325L,R333Q,R333W), two deletions (852T-del, 977C-del), a nonsense mutation (W249X), and a splicing mutations (IVS4nt+1). These 10 mutations except for N314D and P325L,R333W have not been found in Caucasians. Duarte variant with the N314D mutation in Japanese was associated with Sac I (-) in RFLP analysis as well as in Caucasians. We suggest the galactosemic mutation may have occured after racial divergence between Caucasians and Asians, and the N314D mutation may have occured before racial divergence. The GALT activities of all mutants GALT constructs in the COS cell expression system were reduced to 1%-35% of normal constructs, and were correlated with biochemical and clinical phenotypes. Genotyping of the GALT gene can characterize patiens with GALT dificiency, and can be useful for clinical use.
Galactokinase (GALK) is caused by the deficiency of galactokinase. We have independently characterized the sequence of the human GALK gene, which consisted of 8 exons spanning 7.3kb. We have identified five novel mutations in seven Japanese patients with GALK deficiency, which were three missense mutations (R256W,T344M and G349S) and two deletions (405Del-G,505Del-2). These missense mutations led to a drasticredution in GALK activity when indiviual mutant cDNAs were expressed in a mammalian cell system, The results indicate that these missense mutations were the cause of GALK deficiency. These mutations in Japanese have not yet been found in Caucasians.
|
