A recombination hotspot in a schizophrenia-associated region of GABRB2.
BACKGROUND
Schizophrenia is a major disorder with complex genetic mechanisms. Earlier, population genetic studies revealed the occurrence of strong positive selection in the GABRB2 gene encoding the beta(2) subunit of GABA(A) receptors, within a segment of 3,551 bp harboring twenty-nine single nucleotide polymorphisms (SNPs) and containing schizophrenia-associated SNPs and haplotypes.


RESULTS
In the present study, the possible occurrence of recombination in this 'S1-S29' segment was assessed. The occurrence of hotspot recombination was indicated by high resolution recombination rate estimation, haplotype diversity, abundance of rare haplotypes, recurrent mutations and torsos in haplotype networks, and experimental haplotyping of somatic and sperm DNA. The sub-segment distribution of relative recombination strength, measured by the ratio of haplotype diversity (H(d)) over mutation rate (theta), was indicative of a human specific Alu-Yi6 insertion serving as a central recombining sequence facilitating homologous recombination. Local anomalous DNA conformation attributable to the Alu-Yi6 element, as suggested by enhanced DNase I sensitivity and obstruction to DNA sequencing, could be a contributing factor of the increased sequence diversity. Linkage disequilibrium (LD) analysis yielded prominent low LD points that supported ongoing recombination. LD contrast revealed significant dissimilarity between control and schizophrenic cohorts. Among the large array of inferred haplotypes, H26 and H73 were identified to be protective, and H19 and H81 risk-conferring, toward the development of schizophrenia.


CONCLUSIONS
The co-occurrence of hotspot recombination and positive selection in the S1-S29 segment of GABRB2 has provided a plausible contribution to the molecular genetics mechanisms for schizophrenia. The present findings therefore suggest that genome regions characterized by the co-occurrence of positive selection and hotspot recombination, two interacting factors both affecting genetic diversity, merit close scrutiny with respect to the etiology of common complex disorders.
Ng
Siu-Kin
SK
Department of Biochemistry, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region, People's Republic of China.
Lo
Wing-Sze
WS
Pun
Frank W
FW
Zhao
Cunyou
C
Yu
Zhiliang
Z
Chen
Jianhuan
J
Tong
Ka-Lok
KL
Xu
Zhiwen
Z
Tsang
Shui-Ying
SY
Yang
Qiang
Q
Yu
Weichuan
W
Nimgaonkar
Vishwajit
V
Stöber
Gerald
G
Harano
Mutsuo
M
Xue
Hong
H
D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D008957:Models, Genetic; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide; D011963:Receptors, GABA-A / Q000235:genetics*; D011995:Recombination, Genetic; D012559:Schizophrenia / Q000235:genetics*; D017422:Sequence Analysis, DNA
C495710:GABRB2 protein, human; D011963:Receptors, GABA-A