A specific genetic defect in one Chinese family shows that hearing loss was inherited from the female parent.  The defect results from a point mutation — the substitution of a single DNA “base” for another during replication — in the genes of a tiny cellular organ called the mitochondria, which generates a cell’s energy. When reproductive cells come together to form an embryo, the mitochondrial DNA from the mother cell is passed on to the offspring. Evidence has suggested a mother-child inheritance link for hearing loss due to mitochondrial inheritance. Clinical, genetic, molecular and biochemical evidence that a mitochondrial mutation designated tRNAHis 12201 T>C is associated with inherited hearing loss. A large family from eastern China in which 17 of 34 members who descended from the same female ancestor had hearing loss.  Analysis of the mitochondrial genome of the maternal relatives and other tests revealed the site of the hearing loss-related mutation and showed that it impairs the mitochondrial translation and respiration chain.  The findings show that inherited mitochondrial dysfunction is involved in hearing loss and may provide new insights into maternally transmitted hearing loss, valuable information for management and treatment of maternally inherited hearing loss. (By Prof. Min-Xin Guan, http://jmg.bmj.com/content/48/10/682 )