Genetic regulation of the red cell uroporphyrinogen-l-synthetase level in families with acute intermittent porphyria

The uroporphyrinogen-I-synthetase (UIS) activity in red blood cells was determined in 206 individuals from 48 nuclear families ascertained through a proband with acute intermittent porphyria (AIP) as well as in 230 members belonging to 53 nuclear families with no signs of AIP. Complex segregation analysis showed that the UIS activity is regulated by a major locus (a dominant or additive gene) together with a considerable multifactorial component.