Variegate Porphyria Research Articles

Hepatocellular Carcinoma in Acute Hepatic Porphyria: A Meta-Analysis of Observational Studies.

Hepatocellular carcinoma (HCC) is a long-term complication of acute hepatic porphyria (AHP) inclusive of acute intermittent porphyria [AIP], variegate porphyria [VP], or hereditary coproporphyria [HCP]. Data on HCC risk in AHP patients are limited and heterogeneous. We performed this meta-analysis with aims to (a) determine incidence of HCC in AHP and specific subtypes of AHP and (b) examine high-risk groups for HCC. Data from studies reporting HCC development in AHP patients were pooled and reported per 100 person years with 95% confidence intervals (CI). 12 observational (5 prospective) studies (11 Europe and 1 US) on 2735 patients (mean age 54.8 yrs., 62% females) with AHP (80% AIP) were analyzed. 115 HCC cases were observed with HCC incidence per 100 person years of 0.3 (0.2-0.5) in AHP, 0.4 (0.2-0.6) in AIP, 0.3 (0-0.4) in VP, and 0.2 (0.1-0.6) in HCP. The risk was 0.4 (0.2-0.6) in females, 0.3 (0.1-0.5) in males, 0.9 (0.1-1.7) in symptomatic, and 0.5 (0-1.6) in asymptomatic patients. Analyses were heterogeneous with publication bias. AHP patients with HCC were older females with a higher prevalence of cirrhosis, alcohol use, and viral hepatitis. The annual incidence of HCC in AHP patients is 0.3%, with higher risk in AIP, older females, symptomatic patients, and those with other risk factors of liver disease. Future studies pooling individual patient data and overcoming limitations of the current meta-analysis are needed as a basis for deriving a effective screening and surveillance approach for HCC in patients with AHP.

Understanding Hepatic Porphyrias: Symptoms, Treatments, and Unmet Needs.

Hepatic porphyrias are a group of metabolic disorders that are characterized by overproduction and accumulation of porphyrin precursors in the liver. These porphyrins cause neurologic symptoms as well as cutaneous photosensitivity, and in some cases patients can experience life-threatening acute neurovisceral attacks. This review describes the acute hepatic porphyrias in detail, including acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria, as well as the hepatic porphyrias with cutaneous manifestations such as porphyria cutanea tarda and hepatoerythropoietic porphyria. Each section will cover disease prevalence, clinical manifestations, and current therapies, including strategies to manage symptoms. Finally, we review new and emerging treatment modalities, including gene therapy through use of adeno-associated vectors and chaperone therapies such as lipid nanoparticle and small interfering RNA-based therapeutics.

Variegate porphyria onset as neurovisceral manifestation and unusual sensory impairment distribution. Case report

Background: Acute hepatic porphyrias are heme metabolism disorders presenting with a broad clinical spectrum, including neurovisceral manifestations. Peripheral neuropathy is one of the most frequent complications in porphyrias and can correspond about 40 % of the neurovisceral manifestations, and it is mainly attributed to the ALA and PBG accumulation neurotoxicity. The hallmark of an acute porphyric attack is an acute motor axonal neuropathy accompanied by autonomic dysfunction. Sensory impairment is infrequent, and when present, it is classically described as the stocking-glove pattern or, more rarely, a “bathing suit” proximal distribution pattern. Objective: To report a variegate porphyria case in a young patient with unusual sensory manifestations. Methods: A 27-year-old man, previously healthy, present in context of possible arbovirus infeccion with severe abdominal pain, followed by dysautonomia due to orthostatic hypotension, change in urine color and, the emergence of sensory impairment in the trunk and proximal region of the four limbs about twenty days from onset. Dysestesia was severe and marked. Results: Positive clinical features and a urinary exposure test to sunlight corroborate in request genetic testing for acute hepatic porphyrias, with a positive mutation of the PPOX gene in heterozygosis. Discussion: Clinical manifestations with initial presentation of severe dysautonomia followed by sensory changes demarcate neurovisceral involvement of variegate porphyria, adopting an "old-bathing-suit costume" sensory pattern throughout its evolution.

PICO questions and DELPHI methodology for improving the management of patients with acute hepatic porphyria

BackgroundAcute hepatic porphyrias (AHPs) are a group of rare diseases that encompasses acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and 5-aminolaevulinic acid dehydratase deficiency porphyria. Symptoms of AHP are nonspecific which, together with its low prevalence, difficult the diagnosis and follow-up of these patients. Material and methodsThis project used DELPHI methodology to answer PICO questions related to management of patients with AHPs. The objective was to reach a consensus among multidisciplinary porhyria experts providing answers to those PICO questions for improving diagnosis and follow-up of patients with AHP. ResultsTen PICO questions were defined and grouped in four domains: 1. Biochemical diagnosis of patients with AHP. 2. Molecular tests for patients with AHP. 3. Follow-up of patients with AHP. 4. Screening for long-term complications of patients with AHP. ConclusionsPICO questions and DELPHI methodology have provided a consensus on relevant and controversial issues for improving the management of patients with AHP.

Case-based discussion of the acute hepatic porphyrias: Updates on pathogenesis, diagnosis and management.

The acute hepatic porphyrias (AHPs) include three autosomal dominant disorders, acute intermittent porphyria, variegate porphyria and hereditary coproporphyria, and the ultra-rare autosomal recessive 5-aminolevulinic acid dehydratase-deficient porphyria. All four are characterized by episodic acute neurovisceral attacks that can be life-threatening if left untreated. The attacks are precipitated by factors that induce hepatic 5-aminolevulinic acid synthase 1 (ALAS1), resulting in accumulation of the porphyrin precursors, 5-aminolevulinic acid and porphobilinogen, which are believed to cause neurotoxicity. Diagnosis of these rare disorders is often delayed because the symptoms are non-specific with many common aetiologies. However, once clinical suspicion of an AHP is raised, diagnosis can be made by specialized biochemical testing, particularly during attacks. Moderate or severe attacks are treated with intravenous hemin infusions, together with supportive care to relieve pain and other symptoms. Prophylactic treatments are recommended in patients with confirmed recurrent attacks (≥4 attacks in a maximum period of 12 months), the most effective being givosiran, an RNAi therapeutic targeting hepatocyte ALAS1 mRNA. AHP patients with clinically and/or biochemically active disease are at elevated risk for developing long-term complications, including chronic kidney disease, chronic hypertension and hepatocellular carcinoma, thus, surveillance is recommended. Here, using a case-based format, we provide an update on the pathogenesis, diagnosis and treatment of the AHPs based on literature review and clinical experiences.

Insight into the Role of an α-Helix Cluster in Protoporphyrinogen IX Oxidase.

Protoporphyrinogen IX oxidase (PPO) is the last common enzyme in chlorophyll and heme biosynthesis pathways. In humans, point mutations on PPO are responsible for the dominantly inherited disorder disease variegate porphyria (VP). It is found that several VP-causing mutation sites are located on an α-helix cluster (consisting of α-5, α-6, and α-7 helix, named the G169 helix cluster) of human PPO, although these mutation sites are outside the active site of the human PPO. In this work, we investigated the role of the G169 helix cluster via site-directed mutagenesis, enzymatic kinetics, and computational studies. Kinetic studies showed that mutations on the G169 helix cluster affect the activity of PPO. The MD simulation showed that mutations on the G169 helix cluster reduced the activity of PPO by affecting the proper orientation of substrate protoporphyrinogen within the active site of PPO and possibly the dipole moment of the G169 helix cluster. Moreover, the mutation abolished the interaction between the mutated site and other residues, thus affecting the secondary structure and hydrogen bond interactions within the G169 helix cluster. These results indicated that the integrity of the G169 helix cluster is important for the stabilization of protoporphyrinogen within the active site of PPO to facilitate the interaction between protoporphyrinogen and cofactor FAD and provide a proper electrostatic environment for the activity of PPO. Our result provides new insight into understanding the relationship between the structure and function of PPO.

Clinical features of acute attacks, chronic symptoms, and long-term complications among patients with acute hepatic porphyria in Japan: a real-world claims database study

BackgroundAcute hepatic porphyria (AHP) is a family of rare genetic diseases, including acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and delta-aminolevulinic acid dehydratase-deficient porphyria. The objective of this retrospective cohort study was to provide information on the clinical features of AHP in Japan—including acute attacks, chronic symptoms, and long-term complications.MethodsPatients with AHP between April 2008 and June 2020 were selected from Japan’s Medical Data Vision claims database. Patients with AHP were matched 1:10, by sex and age, to patients without AHP. The outcomes were evaluated overall, for patients age ≥ 55 years, and for the matched population.ResultsA total of 391 patients with AHP were included from the Japanese Medical Data Vision database. During the observation period (April 2008–June 2020), 18.2% (71/391) of patients experienced 1 acute attack and 10.5% (41/391) experienced ≥ 2 attacks. Chronic symptoms with rates ~ 10% or higher in the AHP population compared with the matched population included neurotic, stress-related, and somatoform disorders (21.7% vs. 6.7% [15.0% difference]); sleep disorders (23.0% vs. 9.9% [13.1% difference]); other and unspecified abdominal pain (13.6% vs. 3.7% [9.9% difference]); and nausea and vomiting, excluding chemotherapy-induced emesis (17.9% vs. 8.1% [9.8% difference]). Long-term complications with higher incidence rates in the AHP population compared with the matched population included fibrosis and cirrhosis of liver (15.9% vs. 3.0% [12.9% difference]), polyneuropathies and other disorders of the peripheral nervous system (20.5% vs. 7.9% [12.6% difference]), liver cancer (16.9% vs. 4.7% [12.2% difference]), renal failure (16.4% vs. 4.3% [12.1% difference]), and hypertension (26.1% vs. 18.8% [7.3% difference]). Among AHP patients age ≥ 55 years, the most common long-term complications were hypertension, kidney failure, and liver cancer.ConclusionsIn Japan, patients with AHP experience a high clinical burden in terms of acute attacks, chronic symptoms, and long-term complications. The clinical burden related to chronic symptoms and long-term complications was substantially higher in Japanese patients with AHP compared with a matched population without AHP. Recognizing these signs and symptoms of AHP may aid physicians in making an earlier diagnosis, which may help patients avoid attack triggers, implement disease management, and reduce lifetime disease burden.

FRI430 A Case Of Elevated Sex Hormone-binding Globulin Secondary To Variegate Porphyria In A Patient With Hypogonadotropic Hypogonadism

Abstract Disclosure: J. Law: None. C. Yip: Research Investigator; Self; Eli Lilly & Company. Background: Acute porphyria is a group of disorders characterized by enzymatic defects in the heme biosynthetic pathway. The liver is the source of both acute intermittent porphyria (AIP) and variegate porphyria. AIP is known to cause an elevation in sex hormone-binding globulin (SHBG) levels, likely secondary to impaired hepatic function and hepatocyte abnormalities1. We describe a case of elevated SHBG secondary to variegate porphyria, in a male with hypogonadotropic hypogonadism. Case Report: A 44-year-old male presented with an elevated SHBG and symptoms of hypogonadism with low libido, weakness, and fatigue. Fasting morning bloodwork revealed an elevated SHBG at 89 nmol/l (13.5- 71.0), a normal total testosterone level at 12.95 nmol/l (8-32), and a low bioavailable testosterone at 0.82 nmol/l (2.5-10), with confirmatory repeat blood work. His history was significant for longstanding variegate porphyria, manifesting as frequent attacks of abdominal pain. He was on opioids for greater then 10 years for his chronic pain, as well as metoclopramide. On assessment of causes for his elevated SHBG, his TSH was normal at 1.49 mIU/L (0.35-4.30). He did not have cirrhosis, hepatitis, hereditary hemochromatosis, and was not on anticonvulsants. No other cause was found, and his elevated SHBG was deemed secondary to his variegate porphyria. His normal total testosterone level was due to his elevated SHBG, but as mentioned, his bioavailable testosterone was low. His LH and FSH were both inappropriately normal, with his LH being 4.67 IU/L (0.6-12.0) and his FSH 4.7 IU/L (1.0-12.0), in keeping with hypogonadotropic hypogonadism. He went through normal pubertal development and had no anosmia. Workup revealed an elevated prolactin level of 73.8 ug/l (3.5-19.4). He had no galactorrhea or gynecomastia and an MRI sella revealed a normal pituitary gland. His elevated prolactin level was determined to be secondary to his opioid medication and/or metoclopramide use. His hypogonadotropic hypogonadism was deemed secondary to his opioid medications and/or hyperprolactinemia. Conclusion: This case demonstrated variegate porphyria as a likely cause of elevated SHBG, similar to AIP. In patients with variegate porphyria and symptoms of hypogonadism, the SHBG should be measured and if it is elevated, the bioavailable or free testosterone levels should be used in assess instead of relying on the total testosterone levels. As has been previously shown, this case also illustrated the use of opioid medications as a cause of hypogonadotropic hypogonadism.

SAT292 Adrenal Insufficiency Associated With Biallelic Mutations In Porphyria Genes

Abstract Disclosure: C. Smith: None. A. Jackson: None. A. Al-Salihi: None. A. Janecke: None. E. Steichen: None. D. Darby: None. L. Griffin: None. S. Banka: None. S. Elsayed: None. L. Chan: None. L. Metherell: None. Adrenal insufficiency (AI) is life-threatening and can present alone or in combination with other co-morbidities. Here we describe families with a novel association of AI with porphyria caused by biallelic mutations in protoporphyrinogen oxidase (PPOX) or coproporphyrinogen oxidase (CPOX). The porphyrias are a group of disorders caused by defects in one of eight enzymes within the haem biosynthetic pathway, divided into acute porphyrias, resulting in mainly neurovisceral symptoms, or cutaneous porphyrias, mainly affecting the skin. Acute porphyria attacks can be life-threatening, resulting in permanent disability or death. Variegate porphyria and hereditary coproporphyria are associated with autosomal dominant mutations in PPOX and CPOX respectively, with biallelic inheritance rarely reported and knockout mice that are embryonic lethal.We performed whole exome sequencing (WES), array Comparative Genomic Hybridization (aCGH) and whole genome sequencing (WGS) in 3 families with AI and variegate or hereditary porphyria. In kindred 1, with 4 affected individuals, WES revealed a homozygous mutation, p.Glu339Lys, in PPOX. aCGH and WGS revealed no Copy Number Variants (CNVs) and no other variants, in genes causing AI, common to all affected individuals. In families 2 and 3, homozygous mutations in CPOX p.(Pro367Ala) in one patient and p.(Ser28Ter) in two siblings were identified by WGS and WES respectively, with a clinical picture of AI and hereditary coproporphyria. Unlike other acute porphyria kindreds, the heterozygous parents were asymptomatic, manifesting neither porphyria nor AI, suggesting that the level of enzyme function is key for both phenotypes.Reduced PPOX/CPOX activity could cause AI through either; (i) a dearth of haem for steroidogenic CYP450 enzyme action, (ii) toxicity of intermediate porphyrins or (iii) increased oxidative stress. To investigate the mechanism, we first created H295R, human adrenocortical cells, with differing degrees of PPOX-knockdown (KD) by shRNA. Proliferation, measured by MTT assay or GFP accumulation, was lower in PPOX-KD cells at 72 hours and mitochondrial respiration was diminished, possibly due to toxicity of porphyrin precursors. CYP11A1 expression was unaltered whereas STAR and CYP17A1 were significantly lower in PPOX-KD cells. GSH/GSSG ratio, a marker of oxidative stress, was lower in KD cells suggesting increased ROS in these cells. Finally, and definitively, knockdown of at least 60% PPOX protein in H295R cells reduced cortisol output by 2.2-fold (p<0.01) at baseline and 1.9-fold (p<0.0001) in forskolin stimulated cells. Similar CPOX studies are underway.These studies show that cortisol is reduced in individuals with biallelic PPOX/CPOX mutations and, in conjunction with previous cases of AI in association with other genes in the pathway, suggests adrenal function should be monitored in individuals with porphyria. Presentation: Saturday, June 17, 2023

Further Characterization of the Neuroendocrine Phenotype Associated With the PPOX-Related Variegate Porphyria

BackgroundVariegate porphyria is caused by mutations in the PPOX gene; it usually presents in adolescents and adults as an autosomal dominant condition, with cutaneous features or acute peripheral and/or central nervous system crises. A rarer variant, homozygous variegate porphyria, presents in childhood with cutaneous manifestations as well as neurophenotypes. This study sought to further characterize the homozygous PPOX-related neuroendocrine phenotype. MethodsThis study is a retrospective review of the patients’ charts, including their clinical evaluation and molecular genetics, neurodiagnostic, and neuroradiological investigations. ResultsWe describe here three children from a consanguineous family who presented with nystagmus, developmental delay and ataxia, photosensitive skin manifestations, and adrenal insufficiency. Analysis of porphyrins in plasma, urine, and stool together with a genetic study of the PPOX gene confirmed the diagnosis. Interestingly, brain MRI showed severe hypomyelination, a finding rarely reported in variegate porphyria, together with adrenal insufficiency. ConclusionWe recommend analysis of porphyrins in unexplained hypomyelination disorders. Patients with variegate porphyria should be tested for adrenal insufficiency.

769 Reduced expression of PPOX, the variegate porphyria gene, causes intrinsic pathological changes to keratinocytes

769 Reduced expression of PPOX, the variegate porphyria gene, causes intrinsic pathological changes to keratinocytes

A 25-Hour Fast Among Quiescent Hereditary Coproporphyria and Variegate Porphyria Patients is Associated With a Low Risk of Complications

In patients with acute hepatic porphyria (AHP), prolonged fasting is a known trigger of AHP attacks. Despite this, some Jewish AHP patients-mainly hereditary coproporphyria (HCP) and variegate porphyria (VP) patients-fast for 25 consecutive hours during the traditional Jewish holy day known as Yom Kippur. In this study, we evaluated the effect of the fast on these patients. A retrospective study and survey of AHP patients in Israel was carried out. Patients were asked whether they have fasted and whether any symptoms were induced by this fast. Patients' medical records were reviewed for an emergency department (ED) visit following Yom Kippur between 2007 and 2019. Only 3 acute intermittent porphyria (AIP) patients reported fasting; they were excluded from analysis. A total of 21 HCP patients and 40 VP patients completed the survey; 30 quiescent patients reported they fast, while 31 did not fast. The majority of fasting patients (96.67%) reported no symptoms following a fast. We found no statistically significant association between ED visits 1 week (0.26% in both fasting and non-fasting patients) or 1 month (2.1% visits in non-fasting versus 0.78% in fasting patients) following Yom Kippur. Of the symptomatic ED visits following a fast, none were defined as severe attacks. A 25-hour fast in stable HCP and VP patients did not increase the risk of an acute attack and can probably be regarded as safe.

An Overview of Acute Hepatic Porphyrias: Clinical Implications, Diagnostic Approaches, and Management Strategies.

Porphyrias are inborn errors of heme biosynthesis pathway that result in neurovisceral and/ or cutaneous manifestations which occur with episodic attacks, usually accompanied by a multisystemic involvement. Acute hepatic porphyrias include acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and aminolevulinic acid dehydratase deficiency porphyria. Acute hepatic porphyrias may present with symptoms of an affected central, peripheral, and autonomic nervous system and are generally diagnosed in time of an acute neurovisceral attack. In children, clinical picture is more complicated and presents with neurological findings predominantly. First-line investigation should be the urinary porphobilinogen and aminolevulinic acid performance when acute hepatic porphyria is clinically suspected. Comprehensive testing including urine porphyrin separation, fluorescence scanning of diluted plasma at neutral pH, evaluation of fecal porphyrins, and measurement of erythrocyte porphobilinogen deaminase activity is indicated for confirmation or exclusion of the porphyria and define the type of acute hepatic porphyrias. The main aim of the treatment is to decrease aminolevulinic acid, porphobilinogen, and porphyrins by reducing hepatic ALAS1 activity. The first measure should always be the avoidance of any porphyrinogenic drugs. Hemin therapy should not be delayed in the treatment of a severe acute attack. Gonadotropin-releasing hormone analogs and prophylactic hemin protocols can be used for selected cases with more than 4 attacks per year. Givosiran is a promising treatment option for severe cases.

Porphyric neuropathy in black South Africans: a case series

Abstract Porphyria is a rare disorder that results from mutations in the genes important in haem biosynthesis. Several types are described. Acute attacks lead to central, autonomic and peripheral nervous system manifestations. These acute attacks typically occur in acute intermittent porphyria, and less so in variegate porphyria. The neuropathy in this condition can mimic Guillain-Barré syndrome (GBS), and is often misdiagnosed and incorrectly treated. It is rare in general, but considered to be extremely uncommon in the black African population. We describe five black South African patients, three of whom were diagnosed with variegate porphyria, with the presenting manifestation of a severe neuropathy. The neuropathy was atypical in nature and variable in presentation and highlight the importance of considering porphyria in such patients.

Porphyrias: Uncommon disorders masquerading as common childhood diseases.

Porphyrias are a rare group of inborn errors of metabolism due to defects in the heme biosynthetic pathway. The biochemical hallmark is the overproduction of porphyrin precursors and porphyrin species. Afflicted patients present with a myriad of symptoms causing a diagnostic odyssey. Symptoms often overlap with those of common diseases and may be overlooked unless there is heightened clinical suspicion. We are reporting clinical features and diagnostic challenges in four pediatric patients having variegate porphyria, congenital erythropoietic porphyria, acute intermittent porphyria, and erythropoietic protoporphyria (EPP), who presented with diverse multisystem manifestations. This case series illustrates a logical analysis of symptoms and judicious selection of investigations and the role of genotyping in successfully diagnosing porphyrias.

Systematic review of the prevalence and incidence of the photodermatoses with meta-analysis of the prevalence of polymorphic light eruption.

Information about the prevalence of photodermatoses is lacking, despite their substantial impact on life quality. Our objective was to systematically review the literature to establish what is known regarding prevalence and incidence of photodermatoses. We searched Medline, CINAHL and Embase from inception to 2021 to identify original population-based studies in English literature reporting the prevalence and/or incidence of photodermatoses. Information was extracted according to geographical location and risk of bias was assessed using a 10-point risk of bias tool for prevalence studies. Primary outcome was the population prevalence of photodermatoses. Prevalence data for polymorphic light eruption (PLE) were used to calculate the global pooled prevalence of PLE. Twenty-six studies were included; 15 reported prevalence of photodermatoses based on samples of the general population and 11 on prevalence and/or incidence from national and international registry data. The general population studies involved PLE (nine studies), unspecified photosensitivity (2), actinic prurigo (2), juvenile spring eruption (1), chronic actinic dermatitis (1) and variegate porphyria (1), while registry studies reported on cutaneous porphyrias and genophotodermatoses (nine and two studies, respectively). Worldwide the prevalence of PLE between countries ranged from 0.65% (China) to 21.4% (Ireland). The pooled estimated prevalence of PLE was 10% (95% CI 6%-15%) among the general population (n= 19,287), and PLE prevalence increased with distance from the equator (r= 0.78, p< 0.001). While several photodermatoses are rare, photosensitivity can be prevalent at wide-ranging world locations, including Egypt where photosensitivity was found in 4% of children and 10% of adults. This study showed that PLE is highly prevalent in many populations and that its prevalence shows a highly significant correlation with increasing northerly or southerly latitude. Available population-based studies for photodermatoses suggest they can be prevalent at a range of world locations; more attention is required to this area.

Acute hepatic porphyria - classification, diagnosis and treatment

Porphyrias belong to the group of inherited metabolic diseases. Each of the four types of acute hepatic porphyria is caused by a different mutation in the gene of an enzyme involved in the heme biosynthetic pathway. The literature distinguishes between: Acute Intermittent Porphyria (AIP), Hereditary Coproporphyria (HCP), Variegate Porphyria (VP) and Aminolevulinic Dehydratic ADP (ADP) deficiency. -deficient Porphyria). Deficiency of individual enzymes leads to ineffective heme production and accumulation of neurotoxic intermediates - the so-called porphyrins. Two excess metabolites are of major importance in diagnostics - ALA (amionolevulinic acid) and PBG (porphobilinogen). In most cases, the activity of the less functional enzyme is so high that the disease never becomes apparent (latent form). Excessive accumulation of porphyrin precursors is associated with exposure to porphyrinogenic factors, leading to a seizure whose symptoms are closely related to autonomic, peripheral neuropathy, and accompanying neuropsychiatric disorders. In diagnostics, particular attention should be paid to the circumstances of the symptoms and the history of the patient's disease, which often includes numerous episodes of unexplained abdominal pain, which was so severe that it forced the patient to report to emergency departments. A severe attack of porphyria is a medical emergency and requires hospitalization. Failure to diagnose or properly treat it may result in flaccid tetraplegia, respiratory failure, brain edema, coma, and sudden circulation detention.

ALAD Inhibition by Porphobilinogen Rationalizes the Accumulation of δ-Aminolevulinate in Acute Porphyrias.

Patients with major forms of acute hepatic porphyria present acute neurological attacks with overproduction of porphobilinogen (PBG) and δ-aminolevulinic acid (ALA). Even if ALA is considered the most likely agent inducing the acute symptoms, the mechanism of its accumulation has not been experimentally demonstrated. In the most frequent form, acute intermittent porphyria (AIP), inherited gene mutations induce a deficiency in PBG deaminase; thus, accumulation of the substrate PBG is biochemically obligated but not that of ALA. A similar scenario is observed in other forms of acute hepatic porphyria (i.e., porphyria variegate, VP) in which PBG deaminase is inhibited by metabolic intermediates. Here, we have investigated the molecular basis of δ-aminolevulinate accumulation using in vitro fluxomics monitored by NMR spectroscopy and other biophysical techniques. Our results show that porphobilinogen, the natural product of δ-aminolevulinate deaminase, effectively inhibits its anabolic enzyme at abnormally low concentrations. Structurally, this high affinity can be explained by the interactions that porphobilinogen generates with the active site, most of them shared with the substrate. Enzymatically, our flux analysis of an altered heme pathway demonstrates that a minimum accumulation of porphobilinogen will immediately trigger the accumulation of δ-aminolevulinate, a long-lasting observation in patients suffering from acute porphyrias.

Generation and characterization of human U-2 OS cell lines with the CRISPR/Cas9-edited protoporphyrinogen oxidase IX gene

In humans, disruptions in the heme biosynthetic pathway are associated with various types of porphyrias, including variegate porphyria that results from the decreased activity of protoporphyrinogen oxidase IX (PPO; E.C.1.3.3.4), the enzyme catalyzing the penultimate step of the heme biosynthesis. Here we report the generation and characterization of human cell lines, in which PPO was inactivated using the CRISPR/Cas9 system. The PPO knock-out (PPO-KO) cell lines are viable with the normal proliferation rate and show massive accumulation of protoporphyrinogen IX, the PPO substrate. Observed low heme levels trigger a decrease in the amount of functional heme containing respiratory complexes III and IV and overall reduced oxygen consumption rates. Untargeted proteomics further revealed dysregulation of 22 cellular proteins, including strong upregulation of 5-aminolevulinic acid synthase, the major regulatory protein of the heme biosynthesis, as well as additional ten targets with unknown association to heme metabolism. Importantly, knock-in of PPO into PPO-KO cells rescued their wild-type phenotype, confirming the specificity of our model. Overall, our model system exploiting a non-erythroid human U-2 OS cell line reveals physiological consequences of the PPO ablation at the cellular level and can serve as a tool to study various aspects of dysregulated heme metabolism associated with variegate porphyria.

Development and validation of diagnostic algorithms for the laboratory diagnosis of porphyrias.

Porphyrias are rare metabolic disorders of the haem synthesis. They can present with acute neurovisceral attacks, cutaneous symptoms, or a combination of both. As they present with a wide variety of clinical symptoms, diagnosis is often delayed and correct interpretation of porphyria-related tests remains a challenge for many physicians. We developed and validated two algorithms for the laboratory diagnosis of porphyrias based on presenting symptoms. Based on a literature search and clinical/laboratory expertise, we developed algorithms for acute and cutaneous porphyrias. We validated these algorithms using all porphyria related laboratory test requests between January 1st 2000 and September 30th 2020 in UZ Leuven. In addition, we also evaluated our algorithm using samples from the European porphyria network (EPNET) external quality assessment scheme (2010-2021). Sensitivity of the algorithm for acute porphyria was 100.0% [74.9%-100.0%] (13 acute intermittent porphyria (AIP) and 1 variegate porphyria [VP]) with a specificity of 98.5% [91.0%-100.0%] (65 patients). Sensitivity of the algorithm for cutaneous porphyria was 100% [95.1%-100.0%] (7 VP, 59 porphyria cutanea tarda (PCT), 23 erythropoietic protoporphyria (EPP), 2 X-linked erythropoietic protoporphyria [XLEPP]) with a specificity of 93.9% [82.9%-98.5%]. There were no diagnostic samples of other types of porphyria. The algorithms correctly identified 18 of the 19 EPNET porphyria cases. One of the two hereditary coproporphyria cases was missed. The algorithms for acute and cutaneous porphyria showed high sensitivity and specificity and can be used to aid the clinician in correctly interpreting the laboratory findings of porphyria-related tests.