Biallelic CHP1 mutation causes human autosomal recessive ataxia by impairing NHE1 function
by Mendoza Ferreira N, Coutelier M, Janzen E, Hosseinibarkooie S, Lohr H, Schneider S, Milbradt J, Karakaya M, Riessland M, Pichlo C, Torres-Benito L, Singleton A, Zuchner S, Brice A, Durr A, Hammerschmidt M, Stevanin G, Wirth B.
We identified a biallelic 3-bp deletion (p.K19del) in CHP1 that cosegregates with the disease. Neither focused screening for CHP1 variants in 2 cohorts (ARCA: N = 319 and NeurOmics: N = 657) nor interrogating GeneMatcher yielded additional variants, thus revealing the scarcity of CHP1 mutations. We show that mutant CHP1 fails to integrate into functional protein complexes and is prone to aggregation, thereby leading to diminished levels of soluble CHP1 and reduced membrane targeting of NHE1, a major Na+/H+ exchanger implicated in syndromic ataxia-deafness. Chp1 deficiency in zebrafish, resembling the affected individuals, led to movement defects, cerebellar hypoplasia, and motor axon abnormalities, which were ameliorated by coinjection with wild-type, but not mutant, human CHP1 messenger RNA.
Collectively, our results identified CHP1 as a novel ataxia-causative gene in humans, further expanding the spectrum of ARCA-associated loci, and corroborated the crucial role of NHE1 within the pathogenesis of these disorders.