Analysis of the first intron of TNFB gene by NcoI RFLP in Koreans.

The tumor necrosis factor B (TNFB) gene is closely liked with tumor necrosis factor A (TNFA) gene between the HLA-B and C2 genes on chromosome 6p21.3. Several genetic variabilities at the human TNFB loci have been identified, which are the NcoI restriction fragment length polymorphism (RFLP) in the first intron, amino acid substitution at codon 26 of exon 3 and EcoRI RFLP in untranslated exon 4. The NcoI RFLP of TNFB gene gives two allelic fragments of 238/259 bp and 497 bp, corresponding to TNFB1 and TNFB2 alleles, respectively. To investigate the frequency of NcoI RFLP in the first intron of TNFB in Koreans and to compare to that of other ethnic population, genomic DNAs were extracted from leukocytes of 305 unrelated healthy Koreans and amplified the first intron of TNFB gene by PCR. The phenotype frequencies of NcoI RFLP such as TNFB* 1/TNFB1, TNFB1/TNFB2 and TNFB2/TNFB2 were 8.6% (n = 26), 45.2% (n = 138) and 46.2% (n = 141), respectively. The estimated allele frequencies for TNFB1 and TNFB*2 were 0.3115 and 0.6885, respectively. The observed and expected frequencies were in good agreement with the Hardy-Weinberg's equilibrium. The heterozygosity revealed 45.2% and the allele frequencies of NcoI RFLP of TNFB in Koreans were observed comparatively similar to those of other ethnic groups.