ATP6V1B1 and deafness: Thus, dRTA associated with sensorineural deafness is associated with mutations of the gene encoding the B1 subunit of the apical H+-ATPase pump (referred to as ATP6B1 or ATP6V1B1), whilst dRTA without deafness is caused by mutations of the gene encoding a different subunit, ATP6N1B (also referred to as ATP6V0A4), which is an isoform of ATP6N1A that is the 116 kDa non-catalytic accessory subunit of the proton pump.