GCH1 and Ataxia: Brain MRI scans were unremarkable for the following 17 participants: three with postinfectious ataxia, one with ataxia after drowning, one with microduplication in 17q12, and 12 with causal variants in genes ANO3, CSTB, GCH1, GNAO1, KCNA1, PRRT2, RARS2, SLC2A1, and TWNK.