ATP6AP2 and Parkinson disease: A very rare form of parkinsonism (X-linked parkinsonism with spasticity, XPDS) shows pathological 4R TAU deposits and is caused by altered splicing of the ATPase H(+) transporting lysosomal accessory protein 2 (ATP6AP2) gene, which causes lysosomal dysfunction in XPDS [251, 252].