Bachelor of Science

Genetic markers are important tools for the study of human diseases. The persistence of elevated levels of plasma cholesterol transported in low-density lipoproteins (LDL) has been associated with increased risk of coronary heart disease (CHD). Apolipoprotein B (apoB) is the principal ligand for LDL receptor recognition and plays a central role in cholesterol metabolism. High plasma apoB levels are associated with an increased prevalence of atherosclerosis.

The apoB gene is located on chromosome 2p21. A segment of DNA at the 3' end of the apoB gene contains a hypervariable region consisting of variable number of tandem repeats (VNTRs) of short A-T rich DNA sequences (15-17 bp), which are highly variable between individuals. The DNA profiles of the polymorphic region of the apoB gene provide useful information for human DNA fingerprinting studies and disease correlation. In my study, the genetic polymorphism of apoB gene in Chinese, Malay and Indian populations in Singapore are investigated.

Buccal cell samples were collected randomly from 105 Chinese, 68 Indians and 66 Malays. The genetic polymorphism of apoB gene was analysed by the polymerase chain reaction (PCR) and the amplification products were directly visualised after agarose gel electrophorosis.

A total of 26 distinct alleles were identified. The apoB VN'TR alleles in Chinese ranged from 25 to 55 repeats with a mode of 32 repeats. VNTR alleles in Indians ranged from 25 to 48 repeats with a mode of 33 repeats, while the Malays ranged from 27 to 54 repeats with a mode of 30 repeats.

The genetic distances calculated from the results suggest Chinese and Malays are more related, when compared with the Indians, and would most likely share the same ancestral apoB gene. With the relatively high prevalence of CHD in these populations, the genetic polymorphism of apoB VNTRs may be useful as a genetic marker in the study of CHD in Singapore populations.