Identification of a New Plasma «(1,3) Fucosyltransferase (FUT6) Allele Requires an Extended Genotyping Strategy

Abstract

Screening the FUT6 gene of 40 Swedish individuals, originally selected for genotyping of FUT3, revealed an unexpected high frequency of mutations. Four were originally typed as homozygous for the enzyme lethal mutation G739A by Taqal restriction pattern, but only one lacked plasma a(l,3)fucosyltransferase activity. Cloning and sequencing of FUT6 from 2 of them revealed a new allele, without the G739A mutation, but with two new point mutations C738T and G977A. Segregation of this allele was confirmed in Swedish and Indonesian families. Since G739A and C738T mutations are only one nucleotide apart and induce the same modification of Taqal cleavage, a new screening strategy for FUT6 was adopted. The homozygous inactivating G739A mutation was for the first time identified in Caucasian and Polynesian individuals, both lacking plasma enzyme activity. The mutation C370T was present in 25 of the 40 Swedish individuals and the inactivating mutation C945A was not found at all. These findings stress the dangers of transferring restriction enzyme genotype strategies from one population to another and of inferring phenotypes from genotypes without phenotyping and/or performing confirmatory cloning and sequencing.

Molecular Analysis of Plasma α1,3-Fucosyltransferase Deficiency and Development of the Methods for Its Genotyping

“…The 124-bp fragment was then cleaved into two fragments of 101 and 23 bp. A C738T mutation which was not responsible for plasma ·1,3-fucosyltransferase deficiency was previously reported in Swedish individuals [11]. While this point mutation did not result in amino acid change (Phe→ Phe), the C738T mutation interfered with the creation of the RcaI site to detect the G739A mutation in our PCR-RFLP methods.…”

“…Individuals who lacked plasma ·1,3-fucosyltransferase in Java and Sweden were previously reported to belong to Lewis-negative types (le/le) [10,11], but 3 of the 7 individuals in this study were determined to be Lewis positive (Le1/-).…”

“…Previous reports, however, showed genetic variations in the FUT6 genes with a lower frequency of the lethal enzyme mutations in Sweden [11]. In our previous study, 4 of the 44 patients with schizophrenia were found to have a plasma ·1,3-fucosyltransferase deficiency but it remained to be seen whether the FUT6 deficiency was relevant to the incidence of such a mental illness [12].…”

“…The molecular basis for this deficiency was defined with analyses of its unusual occurrence in restricted families in Java [10,11]. The deficiency of the enzyme activity has been shown to result from the mutations occurring in the FUT6 gene; a missense mutation (G739 to A, Glu-247 to Lys) within the catalytic domain and a nonsense mutation (C945 to A, Tyr-315 to stop) truncating the C-terminal of the enzyme [10].…”

“…It was also shown that two codon changes in the FUT6 alleles inactivated the plasma ·1,3-fucosyltransferase, i.e. a missense mutation (G739 to A) in the catalytic domain and a nonsense mutation (C945 to A) truncating the C-terminal of the enzyme [10,11]. Previously, we found for the first time in Japan the presence of plasma ·1,3-fucosyltransferase deficiency in 4 of 44 patients with schizophrenia and analyzed their FUT6 genes [12].…”