We found that la is located in linkage group XVIII. It is highly probable that la and tg are alleles, and closely, linked to Es-1. Mice of the genotype la/tg are abnormal, with clinical signs similar to tg, although more severe. They develop earliest signs at about 15 days of age, similar to la, are runted but fertile and can live for months. Clinical signs are ataixa, stiffness, retarded motor activity and intermittent focal seizures. The pathological basis for these symptoms is still elusive. The three types of mice, la/la, la/tg and tg/tg are thus distinct clinically, la/tg resembling in some respect either of the other two.