Conclusion: Haplogroup D4b, especially subhaplogroup D4b2, may be one of the modifiers associated with the phenotypic expression of hereditary hearing loss (HL). Objectives: The present study investigated the association between suspected hereditary HL and 12 major mtDNA haplogroups in a Japanese population. Besides the mutations of mitochondrial DNA, many modifiers including environmental factors and genetic polymorphisms are involved in HL. Methods: The subjects comprised 373 unrelated Japanese patients with suspected hereditary HL and 480 controls. Twenty of the 373 patients were excluded from the study because the m.1555A>G or the m.3243A>G mutation had been detected in them. The mitochondrial haplotypes were classified into 12 major Japanese haplogroups (i.e. F, B, A, N9a, N9b, M7a, M7b, G1, G2, D4a, D4b, and D5). The frequency of each haplogroup in patients with HL was compared with that of the controls using the chi-squared test. Results: The frequency of the HL patients carrying the mitochondrial haplogroup D4b was significantly higher than that of the controls (37/353 [10.5%] vs 31/480 [6.5%]; OR 1.70 [95% CI 1.032.79, p 0.036]) and evidence for enhancement was found in subhaplogroup D4b2 (32/353 [9.1%] vs 24/480 [5%], OR 1.89 [95% CI 1.093.28, p 0.021]).
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