The "staggerer" mutant is recognized by its staggering gait, mild tremor, hypotonia, and small size. Symptoms develop during postnatal weeks 1 to 4 and remain stationary thereafter. The cerebellar cortex is grossly underdeveloped, with too few granule cells and unaligned Purkinje cells. Genetic linkage studies and neuropathological findings distinguish staggerer from other known mutants.