Trends in erythrocyte protoporphyrin IX concentration by age, sex and season among patients with erythropoietic protoporphyria-20 years of follow-up

BACKGROUND: Erythropoietic protoporphyria (EPP) is an inherited disorder leading to an increased concentration of the photoactive protoporphyrin IX (PpIX) in erythrocytes. Upon photoactivation in the dermal blood vessels and release to the skin, it causes painful skin symptoms when illuminated, depending on PpIX concentration. The present study aimed to investigate if erythrocyte PpIX concentration changes with age in patients with EPP. In addition, we tested gender differences and seasonal variation in erythrocyte PpIX concentration.

METHODS: 53 EPP patients aged 0-90 years were included in this retrospective observational study. A total of 751 blood samples were routinely analyzed for erythrocyte PpIX between 2000 and 2020. Trends in erythrocyte protoporphyrin IX concentration depending on age, sex and season were investigated.

RESULTS: Erythrocyte PpIX levels increased during childhood and youth (median annual increase of 2.7 μmol/L) to reach a stable level in adults though, with a decrease in concentration of about 8% in summer. On average the PpIX level was higher in men (mean of 56 μmol/L, range: 6-139) than women (mean of 38 μmol/L, range: 6-82).

CONCLUSION: We hope that our results can contribute to finding a physiological explanation for the changes in erythrocyte PpIX observed throughout the lives of patients with EPP.