Human subjects carrying heterozygous PUM1 deletions or missense mutations develop a neurodevelopmental disorder referred to as PUM1-associated developmental disability, ataxia, and seizure (PADDAS), associated with a ~ 50% reduction in PUM1 protein, or a later onset variant known as PUM1-related cerebellar ataxia (PRCA), associated with only a ~ 25% lowering of PUM1 levels (Gennarino et al., 2018). The gene discussed is PUM1; the disease is Ataxia.