Longitudinal Analysis of Erythrocyte and Plasma Protoporphyrin Levels in Patients with Protoporphyria

Abstract

Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are inherited cutaneous porphyrias resulting from decreased activity of ferrochelatase and gain-of-function mutations of δ-aminolevulinic acid synthase-2, respectively. Both of these protoporphyrias cause increased protoporphyrin levels that cause photosensitivity and may lead to hepatopathy and further increases in erythrocyte and plasma porphyrin levels. We evaluated erythrocyte protoporphyrin and plasma porphyrin levels in all subjects with EPP (83 subjects) or XLP (9 subjects) without evidence of liver disease tested repeatedly at a single laboratory over 25 years. Intersubject variation contributed more than intrasubject variation (78.86% vs 21.14%) to overall variability, and longitudinal variability, estimated by CV, averaged 26%. Erythrocyte total protoporphyrin levels were similar in males and females with EPP (ratio, 0.99; 95% CI, 0.82-1.21; P = 0.96) but were higher in males than females with XLP, although this difference was not statistically significant (ratio, 0.76; 95% CI, 0.43-1.36; P = 0.35). Analysis of 20 subjects from 9 separate families showed significant effects of family compared with effects of individual variation on total variance (50% vs 25%; P < 0.0001). Variation of erythrocyte total protoporphyrin up to 25% is expected in patients with protoporphyria, whereas greater increases might raise concern for protoporphyric hepatopathy.