Transfer of a human tyrosine hydroxylase transgene into homozygous mice restores perinatal survival and corrects catecholamine levels at adulthood, with rescued mutants appearing normal and healthy for at least 5 to 6 months (J:30273). In heterozygotes, tyrosine hydroxylase activity in embryos and adult tissues is less than 50% of wild-type values, but catecholamine levels are reduced only moderately in the developing animals and maintained normally at adulthood (J:30273).