SLC9A9 and early-onset autosomal dominant Alzheimer disease: NHE6 has been implicated in Parkinsonism and deposition of tau neurofibrillary tangles (Garbern et al., 2010; Riess et al., 2013); similarly, emerging evidence links NHE9 with chronic neurodegenerative conditions, including Alzheimer's disease and multiple sclerosis.