Molecular characterisation and frequency of Gγ Xmn I polymorphism in Chinese and Malay β-thalassaemia patients in Malaysia

The molecular basis of variable phenotypes in β-thalassaemia patients with identical genotypes has been associated with co-inheritance of α-thalassaemia and persistence of HbF production in adult life. The Xmn I restriction site at -158 position of the Gγ-gene is associated with increased expression of the Gγ-globin gene and higher production of HbF. This study aims to determine the frequency of the different genotypes of the Gγ Xmn I polymorphism in β-thalassaemia patients in two ethnic groups in Malaysia.Molecular characterisation and frequency of the Gγ Xmn I polymorphism were studied in fifty-eight Chinese and forty-nine β-thalassaemia Malay patients by Xmn I digestion after DNA amplification of a 650 bp sequence. The in-house developed technique did not require further purification or concentration of amplified DNA before restriction enzyme digestion. The cheaper Seakem ® LE agarose was used instead of Nusieve agarose and distinct well separated bands were observed. Genotyping showed that the most frequent genotype observed in the Malaysian Chinese was homozygosity for the absence of the Xmn I site (-/-) (89.7%). In the Malays, heterozygosity of the Xmn I site (+/-) was most common (63.3%). Homozygosity for the Xmn I site (+/+) was absent in the Chinese, but was confirmed in 8.2% of the Malays. The ratio of the (+) allele (presence of the Xmn I site) to the (–) allele (absence of the Xmn I site)) was higher in the Malays (0.66) compared to the Chinese (0.05). The (+/-) and (+/+) genotypes are more commonly observed in the Malays than the Chinese in Malaysia.