Circadian Rhythms in Acute Intermittent Porphyria—a Pilot Study

Acute intermittent porphyria (AIP) is an inherited disorder of haem synthesis wherein a partial deficiency of porphobilinogen (PBG) deaminase (PBGD) with other factors may give rise to biochemical and clinical manifestations of disease. The biochemical hallmarks of active AIP are relative hepatic haem deficiency and uncontrolled up-regulation of hepatic 5-aminolevulinic acid (ALA) synthase-1 (ALAS1) with over-production of ALA and PBG. The treatment of choice is intravenous haem, which restores the deficient regulatory haem pool of the liver and represses ALAS1. Recently, haem has been shown to influence circadian rhythms by controlling their negative feedback loops. We evaluated whether subjects with AIP exhibited an altered circadian profile.Over a 21-h period, we measured levels of serum cortisol, melatonin, ALA, PBG and mRNA levels (in peripheral blood mononuclear cells) of selected clock-controlled genes and genes involved in haem synthesis in 10 Caucasian (European-American) women who were either postmenopausal or had been receiving female hormone therapy, six of whom have AIP and four do not and are considered controls.Four AIP subjects with biochemical activity exhibited higher levels of PBG and lower levels and dampened oscillation of serum cortisol, and a trend for lower levels of serum melatonin, than controls or AIP subjects without biochemical activity. Levels of clock-controlled gene mRNAs showed significant increases over baseline in all subjects at 5 a.m. and 11 p.m., whereas mRNA levels of ALAS1, ALAS2 and PBGD were increased only at 11 p.m. in subjects with active AIP.This pilot study provides evidence for disturbances of circadian markers in women with active AIP that may trigger or sustain some common clinical features of AIP.