Defects in hydroxymethylbilane synthase (HMBS) can cause Acute Intermittent Porphyria (AIP), an acute neurological disease. Although sequencing-based diagnosis can be definitive, ~⅓ of clinical HMBS variants are missense variants, and most clinically-reported HMBS missense variants are designated as "variants of uncertain significance" (VUS). Using saturation mutagenesis, en masse selection, and sequencing, we applied a multiplexed validated assay to both the erythroid-specific and ubiquitous isoforms of HMBS, obtaining confident functional impact scores for >84% of all possible amino-acid substitutions. The resulting variant effect maps generally agreed with biochemical expectation. However, the maps showed variants at the dimerization interface to be unexpectedly well tolerated, and suggested residue roles in active site dynamics that were supported by molecular dynamics simulations. Most importantly, these HMBS variant effect maps can help discriminate pathogenic from benign variants, proactively providing evidence even for yet-to-be-observed clinical missense variants.

Acute intermittent porphyria (AIP) is a rare hereditary metabolic disease characterized by acute attacks and accumulation of the porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG). Patients with AIP have a high risk of primary liver cancer (PLC). We aimed to assess the association between porphyrin precursor excretion and the risk for PLC in patients with AIP. We studied 48 patients with AIP who developed PLC between 1987 and 2015 and 140 age and sex matched controls with AIP but no PLC. Data on all available urinary PBG and ALA samples collected from 1975 until 1 year before PLC diagnosis were analyzed and compared between cases and controls using logistic regression. Porphyrin precursor excretion was higher in patients with PLC (PBG median 7.9 [IQR 4.4-21.9] mmol/mol creatinine) than in controls (3.8 [1.2-9.8]) (adjusted odds ratio 1.07, 95% confidence interval: 1.02-1.12). None of the 28 patients with all registered samples below the upper limit of normal (ULN) developed PLC, and only one of the 45 patients with all samples <2× ULN developed PLC. Among non-PLC controls, ALA and PBG levels decreased after age 50-60 while an increasing trend was observed after age 65 among those who developed PLC. Increased urinary porphyrin precursors are associated with a high risk of developing PLC. Patients with normal levels appear to have a low risk while high or increasing ALA and PBG after age 65 indicates high risk, which should be considered in surveillance decisions.

The acute hepatic porphyrias (AHP) are associated with long-term complications such as primary liver cancer, hypertension, and chronic kidney disease. Data on other related comorbidities are scarce. In this register-based, matched cohort study, we assessed the risks of nonhepatic cancers, cardiovascular diseases, renal diseases, psychiatric disorders, and mortality in relation to porphyria type, sex, and biochemical disease activity. All patients in the Swedish porphyria register with a verified AHP diagnosis during 1987-2015 were included. The biochemical activity of acute intermittent porphyria was assessed using recorded maximal urinary porphobilinogen (U-PBG). Data on incident comorbidities and mortality were collected from national health registries. Cumulative incidences, rates, and hazards were compared to reference individuals from the general population, matched 1:10 by age, sex, and county. We identified 1244 patients with AHP with a median follow-up of 19 years. Health registries identified 149 AHP-subjects (12.0%) with nonhepatic cancer, similar to 1601 (13.0%) in the matched reference population (n = 12 362). Patients with AHP had a higher risk of kidney cancer (0.8% vs. 0.2%, p < 0.001), hypertension, and chronic kidney disease but no increase in risk for cardiovascular disease, except for cerebrovascular disease in patients with elevated U-PBG, (aHR = 1.40 [95% CI:1.06-1.85]). Mortality risk during follow-up was higher among patients with AHP (21% vs. 18%, p = 0.001), and associated with primary liver cancer, female sex, and biochemical activity. In conclusion, AHP is associated with an increased risk of kidney cancer, hypertension, chronic kidney disease, and mortality but not with cardiovascular disease or other nonhepatic cancers.

The acute hepatic porphyrias (AHP) are associated with a risk of primary liver cancer (PLC), but risk estimates are unclear, and what AHP characteristics that predict PLC risk are unknown. In this register-based, matched cohort study, we assessed the PLC risk in relation to biochemical and clinical porphyria severity, genotype, age, and sex. All patients in the Swedish porphyria register with acute intermittent porphyria (AIP), variegate porphyria (VP), or hereditary coproporphyria (HCP) during 1987‒2015 were included. This AHP cohort was compared with age-, sex-, and county-matched reference individuals from the general population. National register-based hospital admissions for AHP were used to indicate the clinical severity. For AIP, the most common AHP type, patients were stratified by genotype and urinary porphobilinogen (U-PBG). Incident PLC data were collected from national health registers. We identified 1244 individuals with AHP (1063 [85%] AIP). During a median follow-up of 19.5 years, we identified 108 incident PLC cases, including 83 AHP patients (6.7%) and 25 of 12,333 reference individuals (0.2%). The adjusted hazard ratio for AHP-PLC was 38.0 (95% confidence interval: 24.3‒59.3). Previously elevated U-PBG and hospitalizations for porphyria, but not AIP genotype or sex, were associated with increased PLC risk. Patients aged >50 years with previously elevated U-PBG ( n = 157) had an annual PLC incidence of 1.8%. This study confirmed a high PLC risk and identified a strong association with clinical and biochemical AIP activity. Regular PLC surveillance is motivated in patients older than 50 years with a history of active AIP.

Background The acute hepatic porphyrias (AHP) are associated with a risk of primary liver cancer (PLC), but risk estimates are unclear, and what AHP characteristics that predict PLC risk are unknown. In this register-based, matched cohort study, we assessed the PLC risk in relation to biochemical and clinical porphyria severity, genotype, age, and sex. Methods All patients in the Swedish porphyria register with acute intermittent porphyria (AIP), variegate porphyria (VP), or hereditary coproporphyria (HCP) during 1987-2015 were included. This AHP cohort was compared with age-, sex-, and county-matched reference individuals from the general population. National register-based hospital admissions for AHP were used to indicate the clinical severity. For AIP, the most common AHP type, patients were stratified by genotype and urinary porphobilinogen (U-PBG). Incident PLC data were collected from national health registers. Results We identified 1244 individuals with AHP (1063 [85%] AIP). During a median follow-up of 19.5 years, we identified 108 incident PLC cases, including 83 AHP patients (6.7%) and 25 of 12,333 reference individuals (0.2%). The adjusted hazard ratio for AHP-PLC was 38.0 (95% confidence interval: 24.3-59.3). Previously elevated U-PBG and hospitalizations for porphyria, but not AIP genotype or sex, were associated with increased PLC risk. Patients aged >50 years with previously elevated U-PBG (n = 157) had an annual PLC incidence of 1.8%. Conclusion This study confirmed a high PLC risk and identified a strong association with clinical and biochemical AIP activity. Regular PLC surveillance is motivated in patients older than 50 years with a history of active AIP.

With the advent of precision and genomic medicine, a critical issue is whether a disease gene variant is pathogenic or benign. Such is the case for the three autosomal dominant acute hepatic porphyrias (AHPs), including acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria, each resulting from the half-normal enzymatic activities of hydroxymethylbilane synthase, coproporphyrinogen oxidase, and protoporphyrinogen oxidase, respectively. To date, there is no public database that documents the likely pathogenicity of variants causing the porphyrias, and more specifically, the AHPs with biochemically and clinically verified information. Therefore, an international collaborative with the European Porphyria Network and the National Institutes of Health/National Center for Advancing Translational Sciences/National Institute of Diabetes and Digestive and Kidney Diseases (NIH/NCATS/NIDDK)-sponsored Porphyrias Consortium of porphyria diagnostic experts is establishing an online database that will collate biochemical and clinical evidence verifying the pathogenicity of the published and newly identified variants in the AHP-causing genes. The overall goal of the International Porphyria Molecular Diagnostic Collaborative is to determine the pathogenic and benign variants for all eight porphyrias. Here we describe the overall objectives and the initial efforts to validate pathogenic and benign variants in the respective heme biosynthetic genes causing the AHPs.

Variegate porphyria (VP) is an autosomal dominantly inherited hepatic porphyria. The genetic defect in the PPOX gene leads to a partial defect of protoporphyrinogen oxidase, the penultimate enzyme of heme biosynthesis. Affected individuals can develop cutaneous symptoms in sun-exposed areas of the skin and/or neuropsychiatric acute attacks. The identification of the genetic defect in VP families is of crucial importance to detect the carrier status which allows counseling to prevent potentially life threatening neurovisceral attacks, usually triggered by factors such as certain drugs, alcohol or fasting.In a total of 31 Swedish VP families sequence analysis had identified a genetic defect in 26. In the remaining five families an extended genetic investigation was necessary. After the development of a synthetic probe set, MLPA analysis to screen for single exon deletions/duplications was performed.We describe here, for the first time, two partial deletions within the PPOX gene detected by MLPA analysis. One deletion affects exon 5 and 6 (c.339-197_616+320del1099) and has been identified in four families, most probably after a founder effect. The other extends from exon 5 to exon 9 (c.339-350_987+229del2609) and was found in one family. We show that both deletions are mediated by Alu repeats.Our findings emphasize the usefulness of MLPA analysis as a complement to PPOX gene sequencing analysis for comprehensive genetic diagnostics in patients with VP.

Background Acute intermittent porphyria (AIP) is a metabolic disease affecting hepatic heme biosynthesis. The clinical course in overt disease is characterized by acute attacks of neurovisceral symptoms. Treatment is based on symptomatic relief together with carbohydrate loading and in more severe attacks heme therapy. During an acute attack the heme precursors porphobilinogen (PBG) and 5-aminolevulinic acid (ALA) are produced in high amounts by the liver and are found in high concentrations in plasma and urine. These metabolites represent the acute phase reactants confirming an ongoing attack and are used to evaluate therapeutic measures. The aim of this study was to measure PBG and ALA in plasma and urine during an acute attack and to match the biochemical pattern with the clinical and therapeutical course. Methods Three consecutive AIP patients were included during four acute attacks. Plasma PBG and ALA were measured by a LC-MS method and in urine by ion-exchange chromatography. The patients received symptomatic and glucose treatment at admission to hospital, and four days later, if necessary, heme therapy. Results In the three attacks that required heme therapy, plasma PBG concentrations had further increased after admission (p=0.01). In the patient that did not require heme therapy, plasma PBG had decreased after admission. Conclusions Biochemical monitoring of an acute attack was more accurately reflected by plasma PBG than plasma ALA or urinary PBG and ALA. Glucose administration, in contrast to heme therapy, was not sufficient to achieve clinical and biochemical remission in the more serious attacks.

Acute intermittent prophyria is a genetic disorder of haem biosynthesis caused by defects in the gene encoding hydroxymethylbilane synthase on the long arm of chromosome 11. Every effort should be made to identify gene carriers amongst the relatives of patients known to have acute intermittent porphyria as they are at risk of developing potentially fatal neurogenic attacks if exposed to precipitating factors. Erythrocyte hydroxymethylbilane synthase activity was determined in 46 members of two large well characterised families by assaying enzyme activity by both high performance liquid chromatography (HPLC) and fluorimetric assays. Additionally, hydroxymethylbilane synthase immunoreactivity was determined by a sandwich-type ELISA. Statistically significant correlations were observed between erythrocyte hydroxymethylbilane synthase activity assayed by HPLC and by the fluorimetric assay, and enzyme protein concentration (r = 0.85, p < 0.001 and r = 0.80, p < 0.001, respectively). The assay of hydroxymethylbilane synthase immunoreactive concentration in erythrocytes was useful in excluding acute intermittent porphyria in one patient in whom unequivocal assignment of porphyric status was not possible by assaying enzyme activity alone. Erythrocyte hydroxymethylbilane synthase activity assayed by HPLC and fluorimetry showed approximately equal diagnostic performances, both giving rise to a dichotomic distribution of values, with overlap zones of 6% (1/16) and 22% (2/9), respectively, at the "cut off" applied.

Two unrelated families with acute intermittent porphyria (AIP), an autosomal dominant disease related to a defect in porphobilinogen deaminase (PBG-D, EC 4.1.3.8.), were studied with regard to three restriction fragment length polymorphisms (RFLPs) (MspI, PstI, BstNI) within the PBG-D gene. The results indicate that linkage analysis of RFLPs within the gene can be used as a complement to PBG-D analysis for the diagnosis of gene carriers in families with AIP.

Catechol-o-methyltransferase activity in human erythrocytes : a methodological and genetic investigation

Over 200 schizophrenic patients belonging to three major and interrelated complexes have been investigated. A major dominant gene is operating in these pedigrees. Hypotheses that schizophrenia might be caused by gene controlled deficiencies in the catecholamine metabolism were tested in a few selected families. Schizophrenia was significantly associated with decreased activities of dopamine-hydroxylase (DBH) in plasma and monoamine oxidase (MAO) in platelets and with the genetic marker Gc2 (Group specific antigen). There was no significant difference in the catechol-0-methyltransferase (COMT) activity in the red blood cells between schizophrenics and their non-schizophrenic relatives.