The brindled mutation is an X-linked neurological mutation in mice. Male mice hemizygous for the brindled gene have metabolic defects homologous with kinky hair disease in humans. Neuropathologically, the mutation is characterized by extensive neuronal degeneration associated with pronounced mitochondrial changes in cerebral cortex and abnormal arborization of Purkinje cell dendrites, which are most pronounced in the rostral vermis or anterior lobules. In the cerebellum of female mice heterozygous for brindled gene, Purkinje cells with abnormal dendritic arborization and with unusually enlarged mitochondria were also observed. Morphological changes in affected Purkinje cells in young heterozygotes were similar to those of young hemizygotes. However, in older heterozygotes, the changes were far less conspicuous, indicating the presence of some extrinsic factor(s) to compensate expression of the mutant gene in heterozygous brains.