Distribution of apolioprotein E allele frequencies of the Han Chinese in an iodine-deficient mountainous area.

Background: Iodine deficiency is common in the Qinba mountainous area and fetal iodine deficiency disorder (FIDD) is endemic. Our previous study demonstrated that apolipoprotein E (ApoE) was a genetic risk factor for FIDD in the local area.

Aim: In order to achieve a better understanding of the aetiology of iodine deficiency-based mental retardation in the Qinba mountainous area, we conducted further studies of ApoE allele frequencies obtained from the local population.

Subjects and methods: A total of 818 samples from four counties in the iodine-deficient area were recruited for the study of the ApoE genotype and allele frequencies using the PCR-RFLP method, and were subsequently confirmed by sequencing. Results: The frequencies of epsilon2, epsilon3 and epsilon4 alleles of Han Chinese in Qinba were 9.67%, 81.30% and 9.03%, respectively. Furthermore, no significant differences in the distribution of ApoE (either genotype or allele frequencies) between any two subgroups divided according to location, sex and age (p > 0.05) were found. Surprisingly, however, we found a significant difference in the genotype and allele frequencies between Qinba and Shanghai (genotype: chi(2) = 14.91, p = 0.0096; allele: chi(2) = 15.07, p = 0.0009).

Conclusion: The currently documented allele frequencies of ApoE in the Han Chinese population living in the open areas of China do not represent the distribution in the isolated Qinba mountainous area. The higher level of epsilon2 and epsilon4 allele frequencies in the Han Chinese living in the isolated Qinba area arise by chance or may result from genetic adaptation to an environment characterized by malnutrition and iodine deficiency, which may also contribute to the high incidence of mental retardation in these regions.