Porphyrias are inherited or acquired disorders of heme biosynthesis characterized by heme deficiency and accumulation of toxic intermediates. In δ-aminolevulinic acid dehydratase deficiency porphyria (ALADP), patients consistently present elevated urinary δ-aminolevulinic acid (δ-ALA) and coproporphyrin III (COPRO III), yet the mechanistic basis of COPRO III accumulation remains unclear. This metabolic disturbance is also observed in the porphyria-like associated crises in hereditary tyrosinemia type I (HT1). Here, we investigated the effects of δ-ALA, COPRO III, and lead (Pb2+) on human coproporphyrinogen oxidase (CPOX), a key mitochondrial enzyme in heme biosynthesis. Using purified recombinant CPOX, we show that COPRO III binds with high affinity (KD ≈ 2.1 μM) and acts as a competitive inhibitor, while δ-ALA inhibits CPOX at millimolar concentrations through a non-competitive, likely covalent, mechanism. In vivo, δ-ALA accumulation in an HT1 mouse model led to hepatic COPRO III buildup, consistent with our in vitro findings and supporting a synergistic inhibition model in which δ-ALA promotes secondary COPRO III accumulation that further impairs CPOX. Additionally, Pb2+ was found to inactivate CPOX, likely through oxidative damage, providing a molecular explanation for enzyme dysfunction in porphyrin abnormalities in response to lead intoxication. Together, these results identify multiple metabolite- and toxin-dependent mechanisms that converge on CPOX inhibition, offering new insights into the pathophysiology of ALADP, among other porphyrias, lead intoxication, and HT1.

δ-Aminolevulinic acid (ALA) dehydratase (ALAD) deficient porphyria (ADP) is an extremely rare form of porphyria, with only eight documented cases. Herein, we report the second known case of ADP in the Western hemisphere and third case with infantile onset of symptoms. A male neonate presented on day three of life with profound hypotonia, pinpoint pupils, absent deep tendon reflexes, and anemia. Whole genome sequencing revealed two pathogenic missense ALAD variants, and subsequent biochemical testing confirmed a diagnosis of ADP. With supportive care and following erythrocyte transfusions for anemia, his hypotonia improved gradually. Neurological improvement following erythrocyte transfusion may have resulted from suppression of erythropoiesis and less overproduction of ALA and porphyrins by the marrow, which is an important consideration for long term management. This case highlights the importance of leveraging rapid whole genome sequencing for the diagnosis and minimization of devastating sequelae of exceptionally rare disorders, such as ADP.

Postural orthostatic tachycardia syndrome (POTS) is characterized by an excessive heart rate increase upon standing, often associated with dizziness, gastrointestinal symptoms, and decreased functional capacity. Acute hepatic porphyrias (AHP) are rare metabolic disorders with nonspecific neurovisceral and autonomic symptoms, some of which overlap with POTS. The purpose of this study was to evaluate AHP by molecular and biochemical testing in patients with POTS. We studied 50 patients diagnosed with POTS and gastrointestinal symptoms at the Vanderbilt Autonomic Dysfunction Center. They underwent neuro-hormonal evaluation for POTS and genetic and biochemical screening for AHP. Genetic testing was aimed mainly at the four genes relevant to AHPs. Porphobilinogen (PBG), delta-aminolevulinic acid (ALA), and total porphyrins were measured in urine with normalization to creatinine. The average age of the patients was 33 ± 8.6 years, 96% were female, and the average BMI was 28 ± 7.2 kg/m2, average systolic blood pressure was 120 ± 15.5 mmHg, average heart rate was 77 ± 13.6 bpm at baseline, and average SBP was 126 ± 19.1 mmHg. A heart rate of 111 ± 15.8 bpm at 10 min upright, showed normal cardiovascular reflexes. The COMPASS-31 total score was 32 ± 8.4, with a normal autonomic function test. Urine PBG averaged 1 ± 0.7 mg/g creatinine, ALA 2 ± 0.9 mg/g creatinine, and total porphyrins 172 ± 74.2 mmol/g creatinine, which were all normal. None had variants in the four genes associated with AHPs. Three patients were heterozygous for a common low expression ferrochelatase gene variant (FECH). We found no evidence of AHP in patients with POTS with uncontrolled gastrointestinal symptoms, suggesting that screening for AHP, a rare genetic disorder, may not be warranted.

This study aimed to characterise symptoms and assess the prevalence of elevated urine porphyrin precursors in first-degree relatives of acute hepatic porphyria (AHP) patients who have never experienced acute attacks and had no previous AHP genetic or biochemical testing. 149 first-degree relatives of confirmed AHP patients, previously unscreened for the family mutation, were recruited. All underwent genetic analysis, with 143 completing a study questionnaire and 118 undergoing urine analysis for delta aminolevulinic acid (ALA) and porphobilinogen (PBG). The questionnaire focused on symptoms, medical and family history, and quality of life. The study included 79 AHP mutation carriers and 70 non-carriers. Carriers had significantly higher ALA (6.98 vs. 2.21 mg/g creatinine) and PBG levels (9.17 vs. 1.31 mg/g creatinine) than non-carriers. Female carriers showed higher ALA (9.29 vs. 3.07 mg/g creatinine) and PBG levels (12.71 vs. 3.16 mg/g creatinine) than male carriers. Porphyria-related symptoms were reported by 27% (21/77) of carriers compared to 15% (10/66) of non-carriers, with carriers more likely to report dark urine and prolonged symptoms. Finally, 30.8% of carriers were asymptomatic high excreters (ASHE) with PBG levels exceeding four times the upper limit of normal (ULN). Significant differences in porphyrin precursor excretion and symptom profiles were found between AHP mutation carriers and controls, as well as between female and male carriers. Female carriers are more likely to excrete porphyrin metabolites above the normal range. A larger than expected number of undiagnosed carriers are ASHE with levels greater than four times the ULN.

Acute hepatic porphyria (AHP), a rare genetic disorder, causes life-threatening porphyria attacks and chronic pain and impairs daily functioning and quality of life. Recently, a new siRNA therapy, givosiran, became available for AHP. This open-label, multicenter, single-arm study expanded access to givosiran and further explored its safety and efficacy in 10 Japanese patients with AHP. Participants received monthly subcutaneous injections of givosiran (2.5 mg/kg). Three patients were continued from the phase III ENVISION study of givosiran, and seven were newly recruited. Assessments comprised clinical AHP features, urinary aminolevulinic acid (ALA) and porphobilinogen (PBG) levels, use of hemin to treat attacks, and the Givosiran Patient Experience Questionnaire (GPEQ). Urinary ALA and PBG levels remained at or below upper limits of normal levels throughout the study. The GPEQ showed symptomatic improvement in eight participants. Of the eight adverse events, five were deemed by the investigator to be related to givosiran. One patient experienced two attacks, which required urgent healthcare visits but no hemin use. Generally, the safety profile was consistent with that previously observed. All adverse events were nonserious, and no deaths occurred. The study indicates that monthly givosiran administration is safe and clinically useful in Japanese patients with AHP.