VMA21 and deafness: In the total cohort of patients, only minor clinical symptoms were observed that overlap with symptoms from known genetic defects in the V-ATPase, including deafness (ATP6V1B1 and ATP6V0A4) and muscle weakness, as reported for X-linked Myopathy with Excessive Autophagy (XMEA, MIM 310440) due to mutations in V-ATPase assembly factor VMA21 (ref. 29).