There are several known examples of mutations which influence copper homeostasis in humans and animals. Pleiotropic effects are observed when the mutant gene disturbs copper flux. In some cases, the mutation alters the level of a specific copper ligand (enzyme) and the clinical consequences are unique. The two most widely studied genetic maladies in humans are Menkes' and Wilson's diseases. Menkes' disease is an X-linked fatal disorder in which copper accumulates in some organs (intestine and kidney) and is low in others (liver and brain). Wilson's disease is an autosomal recessive disorder in which copper accumulates, if untreated, in liver and subsequently in brain and kidney. Pathophysiological consequences of copper deficiency and toxicity characterize these two disorders. Specific mutations of human cuproenzymes include overproduction of copper-zinc superoxide dismutase in Down's syndrome, absence of tyrosinase in albinism, hereditary mitochondrial myopathy due to reduction in cytochrome c oxidase, and altered lysyl oxidase in X-linked forms of cutis laxa and Ehlers-Danlos syndrome. Mutations altering copper metabolism are also known in animals. Several murine mutants have been studied. The most extensively investigated mutants are the mottled mice, in particular brindled mice, which have a mutation analogous to that of Menkes' disease. Another recently described murine mutation is toxic milk (tx) an autosomal recessive disorder that is characterized by copper accumulation in liver. Two other mutants, crinkled and quaking, were once thought to exhibit abnormal copper metabolism. Recent data has not confirmed this. A mutation in Bedlington terriers has been described which is very similar to Wilson's disease.(ABSTRACT TRUNCATED AT 250 WORDS)