Congenital erythropoietic porphyria (Günther's disease): enzymatic studies on two cases of late onset.

Cosynthetase was measured in hemolysates of two patients with CEP that appeared in adulthood. The level of cosynthetase activity was found to be very low (mean 18% of normal), ruling out the hypothesis of heterozygous cases. Several obligatory heterozygous carrier were also studied in whom cosynthetase activity was found to be intermediate (mean 46.66% of normal) between the levels of normal controls and homozygous patients whereas PBG deaminase was always normal. The nature of the metabolic abnormality is undoubtedly a primary defect of the cosynthetase activity; some cases of late onset emphasize the heterogeneity of the disease.