Loss-of-function mutations in the ER-resident protein Snx14 is the cause of spinocerebellar ataxia autosomal recessive 20 (SCAR20) characterized by intellectual impairment, cerebellar atrophy, ataxia and defective speech development (Thomas et al., 2014). Here, PROS1 is linked to autosomal recessive spinocerebellar ataxia 20.