Cacna1a^tg-la, leaner, recessive. The leaner mutation arose spontaneously in the AKR/J strain. Homozygotes are recognized at 8 to 10 days of age by ataxia, stiffness, and retarded motor activity. Adults are characterized by instability of the trunk, and hypertonia of trunk and limb muscles. Seizures have not been observed (J:28459). Heterozygous Cacna1a^tg-la/Cacna1a^tg mice show ataxia, stiffness, and retarded motor activity at 15 to 17 days of age. Within a few days they develop a wobbly gait and intermittent focal seizures that continue throughout life (J:5240). The cerebellum is reduced in size, particularly in the anterior region, in Cacna1a^tg-la homozygous mice (J:28459). There is loss of granule cells beginning at 10 days of age and loss of Purkinje and Golgi cells beginning after 1 month. Cell loss later slows but continues throughout life. Granule and Purkinje cells are more severely affected than Golgi cells and the anterior folia more severely affected than other parts of the cerebellum (J:6909). Heckroth and Abbott (J:20921) found loss of Purkinje cells from alternating sagittal zones of the cerebellum in Cacna1a^tg-la homozygotes. The cerebellum of Cacna1a^tg-la/Cacna1a^tg heterozygotes shows shrinkage and degenerative changes of the Purkinje cells (J:5240). The loss in cerebellar volume in these and in homozygous Cacna1a^tg mice is specific to the molecular layer, with no change in volume of the granule cell or white matter layers (J:22482). Many Cacna1a^tg-la homozygotes die at weaning time, but some survive and females may breed (J:28459).