Background: Male-pattern baldness (androgenetic alopecia, AGA) is the most common form of hair loss among humans. Research has shown that it is caused by genetic factors. Numerous studies have unequivocally identified two major genetic risk loci for AGA: the X-chromosomal AR/EDA2R-locus; and the PAX1/FOXA2-locus on chromosome 20. Objectives: To identify further candidate genes for AGA, and thus gain further insights into this phenotype. Methods: A German sample of 581 severely affected cases and 617 controls was used to perform a genome-wide association study. The identified associated locus was further analyzed by fine-mapping, and then independently replicated in an Australian sample. Expression and pathway analyses were performed to characterize the identified susceptibility gene. Results: The most significant association signal was obtained for rs756853 (P=1.64x10(-7) ), which is located intronically in the histone deacetylase 9 (HDAC9) gene. Fine-mapping and a family-based analysis revealed that rs756853 and the 6kb distal rs2249817 were the most highly associated SNPs. The association finding was replicated in an independent Australian sample, when the analysis was restricted to severely affected cases and unaffected controls (P=0.026). Analysis of rs2249817 in a combined sample of severely affected German and Australian cases and unaffected controls revealed a strong association signal with P=9.09x10(-8) . Tissue expression studies demonstrated HDAC9 expression in various tissues, including tissues of relevance to AGA. No strong genotypic effects were observed in genotype-specific expression or splice studies. Pathway analyses supported the hypothesis that HDAC9 plays a functional role in AGA via interaction with the AR gene. Conclusions: The present study suggests that HDAC9 is the third AGA susceptibility gene.
Copyright © 2011 British Association of Dermatologists.
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