Loss of function of a calcium channel underlies human deafness and is also associated with cardiac arrhythmia, reports a study published online this week in Nature Neuroscience. These findings provide insight into hearing and deafness in humans and highlight the need for cardiac testing in cases of deafness where the cause is unknown.
A certain type of ion channel that allows calcium to enter cells, L-type calcium channel, is critical for both the function of auditory hair cells, which are critical for hearing, and the function of the sinoatrial node (SAN), which is critical for the heart’s rhythm.
Hanno Bolz and colleagues identified a mutation in CACNA1D, a gene that encodes the pore-forming part of the L-type calcium channel, in two families where many blood relatives were deaf. All deaf individuals also exhibited pronounced SAN dysfunction with abnormally slow heartbeat at rest. Further investigation of the mutant calcium channels revealed that the mutation resulted in calcium ions not being able to get through channel. The loss of function of the mutant calcium channels is consistent with altered electrical excitability in auditory and SAN cells and could underlie both the deafness and SAN dysfunction seen in these deaf individuals.