Hypertrophic cardiomyopathy (HCM) is a significant cause of sudden unexpected cardiac death in any age group. Here we reported a Chinese family with maternally transmitted HCM and atrioventricular block (AVB). DNA sequencing analysis identified a novel homoplasmic 2336T>C mutation, which disturbs the 2336U-A2438 base pair in the stem-loop structure of mitochondrial 16S rRNA domain III. Functional and structural assays, including oxygen consumption rate, ATP synthesis, reactive oxidative species (ROS) production and electron microscopy, indicated that mitochondrial damages were present in the lymphoblastoid cells carrying 2336T>C mutation. Our findings provide a new insight in the pathogenesis of HCM. (By Professor Qingfeng Yan, http://jmg.bmj.com/content/early/2013/12/23/jmedgenet-2013-101818 )