Elsevier

Legal Medicine

Volume 15, Issue 5, September 2013, Pages 239-243
Legal Medicine

A hypervariable STR polymorphism in the CFI gene: Southern origin of East Asian-specific group H alleles

https://doi.org/10.1016/j.legalmed.2013.04.001Get rights and content

Abstract

Previous studies of four populations revealed that a hypervariable short tandem repeat (iSTR) in intron 7 of the human complement factor I (CFI) gene on chromosome 4q was unique, with 17 possible East Asian-specific group H alleles observed at relatively high frequencies. To develop a deeper anthropological and forensic understanding of iSTR, 1161 additional individuals from 11 Asian populations were investigated. Group H alleles of iSTR and c.1217A allele of a SNP in exon 11 of the CFI gene were associated with each other and were almost entirely confined to East Asian populations. Han Chinese in Changsha, southern China, showed the highest frequency for East Asian-specific group H alleles (0.201) among 15 populations. Group H alleles were observed to decrease gradually from south to north in 11 East Asian populations. This expansion of group H alleles provides evidence that southern China and Southeast Asia are a hotspot of Asian diversity and a genetic reservoir of Asians after they entered East Asia. The expected heterozygosity values of iSTR ranged from 0.927 in Thais to 0.874 in Oroqens, higher than those of an STR in the fibrinogen alpha chain (FGA) gene on chromosome 4q. Thus, iSTR is a useful marker for anthropological and forensic genetics.

Introduction

Population-specific or regionally private alleles are powerful markers to understand human migration and expansion in anthropology and to identify the ancestry of an individual in forensic science. Short tandem repeat (STR) loci are highly polymorphic and useful genetic markers in these fields. However, no population-specific or regionally private STR alleles with a frequency above 0.13 have been found, except for allele 9RA at D9S1120 locus, which is ubiquitous at an average frequency of 0.329 in North and South American populations and 0.207 in Western Beringian populations. This geographically limited distribution of allele 9RA implies that Western Beringians contributed to all modern Native American populations [1]. Allele 9RA at D9S1120 locus is useful as an ancestry-informative marker for native Americans [2], [3].

Complement factor I (CFI) is a serine protease with an important role in complement alternative pathway regulation. The human CFI gene spans 63 kb on chromosome 4q25 and consists of 13 exons, encoding a 583-amino acid polypeptide [4]. A short tandem repeat (iSTR, refSNP ID rs56875356), observed at intron 7, is hypervariable with expected heterozygosity ranging from 0.889 in a German population to 0.927 in a Thai population. iSTR consists of 42 normal and intermediate alleles, of which 25 (alleles 16–34), belonging to group L, are common in four investigated populations. The remaining 17 (alleles 37.3–55.3), belonging to group H, were observed in mainland Japanese (J-Tottori) and Thai populations, but not in sub-Saharan African and German populations, suggesting that group H alleles are population-specific. The repeat structure is distinct between these two group alleles: group L alleles have a consensus structure of (TTTC)nC(TTTC)4, where n is 12–30, and group H alleles, of (TTTC)p(TTCC)qTTC(TTTC)rC(TTTC)3, where p + q + r is 34–52. An STR in the fibrinogen alpha chain gene (FGA) is located on chromosome 4q and is about 45 Mb distant from iSTR. No linkage disequilibrium (LD) was observed between them. Thus, iSTR was suggested to be a useful supplementary genetic marker in forensic science [5], [6]. We also elucidated the molecular basis of the CFI protein polymorphism and investigated five single-nucleotide polymorphisms on exons of the CFI gene (iSNPs) in 20 worldwide populations. There was a significant correlation between frequencies of c.1217A (p.406H) allele in exon 11 and the degree of latitude in 15 East Asian populations, showing a south–north downward geographic cline [7]. The association was observed between c.1217A and group H alleles in J-Tottori and Thai populations [5]. To evaluate the more detailed geographic patterns of iSNPs and iSTR at the CFI gene, in this study we investigated 1161 unrelated subjects from 11 Asian populations.

Section snippets

Materials and methods

A total of 1161 unrelated individuals from 11 Asian populations were investigated (Tables S1–S5). Of them, eight populations were selected from the 20 populations investigated in a previous study of the five iSNPs: Turk, Indian, Mongolian (M-Khalha), Korean (K-Seoul), Okinawan Japanese (J-Okinawa), and Han Chinese (H-Wuxi, H-Changsha and H-Huizhou) [7]. The remaining three populations were Tibetans in Kathmandu, Nepal, Evenkis in the Inner Mongolia Autonomous Region, China, and Oroqens in

Typing of five iSNPs

Table S1 shows the frequencies of the five iSNPs. The frequency of c.1217A allele in the three additional populations ranged from 0.095 in Tibetans to 0.012 in Oroqens. The two populations in the northern part of East Asia showed evidently low frequencies. These findings confirmed a south–north downward geographic cline of the c.1217A allele frequency in 18 East Asian populations (r = −0.8842, p < 0.001). H-Changsha showed the highest frequency of 0.150 among the 23 investigated populations. The

Discussion

The human iSTR has experienced two important events to generate groups L and H alleles in the process of human evolution. Chimpanzee, gorilla and Japanese monkey have the sequence of (TTTC)3(T/CTTC)T13–14 in the corresponding region [5]. RepeatMasking (http://www.repeatmasker.org/) showed AluYc element in the short sequence data from the three primates and humans [5] and AluSg7 element in the long human sequence data from a database (http://www.ncbi.nlm.nih.gov/gene/3426). An Alu element

Acknowledgements

This study was supported in part by Grants-in-Aid for Scientific Research (20590678 and 23590849 to IY) from the Japan Society for the Promotion of Science.

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