Consistent with the temporal changes in gross cerebellar size, PN firing frequency, and behavior, ML width in AtmR35X/R35X; Aptx−/− mice was normal in younger mice but progressively decreased in width as the severity of ataxia increased (P400: 120.2±2.1 μm [n=5] vs. 140.2±4.8 μm [n=5], two-way ANOVA, F(1, 42)=45.04, p<0.0001; Figure 5B and, Figure 5—figure supplement 1). The gene discussed is APTX; the disease is Ataxia.