VMA21 and X-linked myopathy with excessive autophagy: One subunit of the V1 domain is linked to human genetic disease (ATP6V1B1 (MIM 267300)) resulting in renal tubular acidosis with deafness, while previously one of the V-ATPase assembly factors, VMA21, has been linked to XMEA (X-linked myopathy with excessive autophagy (MIM 310440) (ref. 29)).