Family study of acute intermittent porphyria and hereditary coproporphyria in Niigata and Akita prefectures, Japan

Simple screening tests, urinary porphobilinogen (PBG) for acute intermittent porphyria (AIP) and fecal coproporphyrin for hereditary coproporphyria (HCP), were performed in a family study of AIP and HCP. Urinary PBG was positive in 93 of 211 members of 10 AIP families, but was negative in 568 of 572 controls. Fecal coproporphyrin was positive in 54 of 108 members of 10 HCP families, but was negative in 188 controls. A dominant inheritance was assumed by a chi-square test and Weinberg segregation ratio. Worsening factors around puberty were suggested by the onset age and cumulative percentage of genetically loaded cases. Sex-related expression of symptoms was also inferred by a higher incidence of both porphyrias in females than in males. Fitness and penetrance of both porphyrias were good. An l-triiodothyronine loading test was the most useful for the detection of masked carriers of AIP. In conclusion, AIP and HCP in Japan show a dominant inheritance with sex-related metabolic and clinical manifestations.