The 12S rRNA A1555G mutation in the mitochondrial haplogroup D5a is responsible for maternally inherited hypertension and hearing loss in two Chinese pedigrees

We reported here clinical, genetic evaluations and molecular analysis of mitochondrial DNA (mtDNA) in two Han Chinese families carrying the known mitochondrial 12S rRNA A1555G mutation. In contrast with the previous data that hearing loss as a sole phenotype was present in the maternal lineage of other families carrying the A1555G mutation, matrilineal relatives among these two Chinese families exhibited both hearing loss and hypertension. Of 21 matrilineal relatives, 9 subjects exhibited both hearing loss and hypertension, 2 individuals suffered from only hypertension and 1 member had only hearing loss. The average age at onset of hypertension in the affected matrilineal relatives of these families was 60 and 46 years, respectively, whereas those of hearing loss in these two families were 33 and 55 years, respectively. Molecular analysis of their mtDNA identified distinct sets of variants belonging to the Eastern Asian haplogroup D5a. In contrast, the A1555G mutation occurred among other mtDNA haplogroups D, B, R, F, G, Y, M and N, respectively. Our data further support that the A1555G mutation is necessary but by itself insufficient to produce the clinical phenotype. The other modifiers are responsible for the phenotypic variability of matrilineal relatives within and among these families carrying the A1555G mutation. Our investigation provides the first evidence that the 12S rRNA A1555G mutation leads to both of hearing loss and hypertension. Thus, our findings may provide the new insights into the understanding of pathophysiology and valuable information for management and treatment of maternally inherited hearing loss and hypertension.