Probable cation-transporting ATPases 13A4 and 13A5 (ATP13A4, 5) belong to the P5 subfamily of P-tpre ATPases. This subfamily is the most poorly understood in terms of chracterisation and function. The yeast orthologue YPK9 (aka Yor291w) shows toxicity when deleted from yeast cells, suggesting a role in sequestration of divalent heavy metal ions (Schmidt et al. 2009). The ATP13A4 gene may be disrupted by a 3q25-q29 inversion of the long arm of chromosome 3, which may result in a specific language impairment (SLI) (Kwasnicka-Crawford et al. 2005).