delta-Aminolevulinate dehydratase (ALAD) porphyria: the first case in North America with two novel ALAD mutations

From chemistry to genomics: A concise history of the porphyrias

We describe developments in understanding of the porphyrias associated with each step in the haem biosynthesis pathway and the role of individuals whose contributions led to major advances over the past 150 years. The first case of erythropoietic porphyria was reported in 1870, and the first with acute porphyria in 1889. Photosensitisation by porphyrin was confirmed by Meyer-Betz, who self-injected haematoporphyrin. Günther classified porphyrias into haematoporphyria acuta, acuta toxica, congenita and chronica. This was revised by Waldenström into porphyria congenita, acuta and cutanea tarda, with the latter describing those with late-onset skin lesions. Waldenström was the first to recognise porphobilinogen's association with acute porphyria, although its structure was not solved until 1953. Hans Fischer was awarded the Nobel prize in 1930 for solving the structure of porphyrins and the synthesis of haemin. After 1945, research by several groups elucidated the pathway of haem biosynthesis and its negative feedback regulation by haem. By 1961, following the work of Watson, Schmid, Rimington, Goldberg, Dean, Magnus and others, aided by the availability of modern techniques of porphyrin separation, six of the porphyrias were identified and classified as erythropoietic or hepatic. The seventh, 5-aminolaevulinate dehydratase deficiency porphyria, was described by Doss in 1979. The discovery of increased hepatic 5-aminolaevulinate synthase activity in acute porphyria led to development of haematin as a treatment for acute attacks. By 2000, all the haem biosynthesis genes were cloned, sequenced and assigned to chromosomes and disease-specific mutations identified in all inherited porphyrias. These advances have allowed definitive family studies and development of new treatments.

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.

Acute hepatic porphyrias-A guide for hepatologists

The acute hepatic porphyrias (AHPs) are a group of rare, inherited disorders of the heme biosynthesis pathway, usually manifesting with attacks of acute abdominal pain and other neurovisceral symptoms, with or without cutaneous manifestations. AHPs are characterized by the accumulation of porphyrin precursors, porphobilinogen, and/or aminolevulinic acid, in the blood. The diagnosis is often missed or delayed due to both inadequate testing and the improper use of available laboratory tests. In this review, we describe the various clinical presentations of the 4 AHPs, elucidate the approach to diagnosis, and provide recommendations for immediate and long-term management. We also describe the different complications that can occur with long-standing AHP, including the development of HCC. The AHPs are very treatable conditions, with excellent outcomes if diagnosed and treated early. A high index of suspicion for the presence of these disorders, along with accurate testing and timely treatment, will help reduce the burden of disease and prevent irreversible complications in patients with AHP.

AGA Clinical Practice Update on Diagnosis and Management of Acute Hepatic Porphyrias: Expert Review

DESCRIPTION

The acute hepatic porphyrias (AHP) are rare, inborn errors of heme-metabolism and include acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and porphyria due to severe deficiency of 5-aminolevulinic acid dehydratase. Acute intermittent porphyria is the most common type of AHP, with an estimated prevalence of patients with symptoms of approximately 1 in 100,000. The major clinical presentation involves attacks of severe pain, usually abdominal and generalized, without peritoneal signs or abnormalities on cross-sectional imaging. Acute attacks occur mainly in women in their childbearing years. AHP should be considered in the evaluation of all patients, and especially women aged 15-50 years with recurrent severe abdominal pain not ascribable to common causes. The screening tests of choice include random urine porphobilinogen and δ-aminolevulinic acid corrected to creatinine. All patients with elevations in urinary porphobilinogen and/or δ-aminolevulinic acid should initially be presumed to have AHP. The cornerstones of management include discontinuation of porphyrinogenic drugs and chemicals, administration of oral or intravenous dextrose and intravenous hemin, and use of analgesics and antiemetics. Diagnosis of AHP type can be confirmed after initial treatment by genetic testing for pathogenic variants in HMBS, CPOX, PPOX, and ALAD genes. AHP is also associated with chronic symptoms and long-term risk of systemic arterial hypertension, chronic renal and liver disease, and hepatocellular carcinoma. Patients who have recurrent acute attacks (4 or more per year) should be considered for prophylactic therapy with intravenous hemin or subcutaneous givosiran. Liver transplantation is curative and reserved for patients with intractable symptoms who have failed other treatment options.

METHODS

This expert review was commissioned and approved by the American Gastroenterological Association (AGA) Institute Clinical Practice Updates Committee (CPUC) and the AGA Governing Board to provide timely guidance on a topic of high clinical importance to the AGA membership, and underwent internal peer review by the CPUC and external peer review through standard procedures of Gastroenterology. These Best Practice Advice (BPA) statements were drawn from a review of the published literature and from expert opinion. Because systematic reviews were not performed, these BPA statements do not carry formal ratings of the quality of evidence or strength of the presented considerations. Best Practice Advice Statements BEST PRACTICE ADVICE 1: Women aged 15-50 years with unexplained, recurrent severe abdominal pain without a clear etiology after an initial workup should be considered for screening for an AHP. BEST PRACTICE ADVICE 2: Initial diagnosis of AHP should be made by biochemical testing measuring δ-aminolevulinic acid, porphobilinogen, and creatinine on a random urine sample. BEST PRACTICE ADVICE 3: Genetic testing should be used to confirm the diagnosis of AHP in patients with positive biochemical testing. BEST PRACTICE ADVICE 4: Acute attacks of AHP that are severe enough to require hospital admission should be treated with intravenous hemin, given daily, preferably into a high-flow central vein. BEST PRACTICE ADVICE 5: In addition to intravenous hemin, management of acute attacks of AHP should include pain control, antiemetics, management of systemic arterial hypertension, tachycardia, and hyponatremia, and hypomagnesemia, if present. BEST PRACTICE ADVICE 6: Patients should be counseled to avoid identifiable triggers that may precipitate acute attacks, such as alcohol and porphyrinogenic medications. BEST PRACTICE ADVICE 7: Prophylactic heme therapy or givosiran, administered in an outpatient setting, should be considered in patients with recurrent attacks (4 or more per year). BEST PRACTICE ADVICE 8: Liver transplantation for AHP should be limited to patients with intractable symptoms and significantly decreased quality of life who are refractory to pharmacotherapy. BEST PRACTICE ADVICE 9: Patients with AHP should be monitored annually for liver disease. BEST PRACTICE ADVICE 10: Patients with AHP, regardless of the severity of symptoms, should undergo surveillance for hepatocellular carcinoma, beginning at age 50 years, with liver ultrasound every 6 months. BEST PRACTICE ADVICE 11: Patients with AHP on treatment should undergo surveillance for chronic kidney disease annually with serum creatinine and estimated glomerular filtration rate. BEST PRACTICE ADVICE 12: Patients should be counseled on the chronic and long-term complications of AHP, including neuropathy, chronic kidney disease, hypertension, and hepatocellular carcinoma, and need for long-term monitoring.

Rare, Overlooked, or Underappreciated Causes of Recurrent Abdominal Pain: A Primer for Gastroenterologists

Recurrent abdominal pain is a common reason for repeated visits to outpatient clinics and emergency departments, reflecting a substantial unmet need for timely and accurate diagnosis. A lack of awareness of some of the rarer causes of recurrent abdominal pain may impede diagnosis and delay effective management. This article identifies some of the key rare but diagnosable causes that are frequently missed by gastroenterologists and provides expert recommendations to support recognition, diagnosis, and management with the ultimate aim of improving patient outcomes.

Case Report: Lack of Response to Givosiran in a Case of ALAD Porphyria

Introduction: 5-Aminolevulinic acid dehydratase (ALAD) porphyria (ADP) is an autosomal recessive disease characterized by a profound deficiency in ALAD, the second enzyme in the heme biosynthetic pathway, and acute neurovisceral attacks with abdominal pain and peripheral neuropathy. Hemin infusions are often effective in treating and preventing such attacks. Givosiran was recently approved for prevention of attacks of acute hepatic porphyrias (AHPs), including ADP, but, to our knowledge, has not yet been applied in patients with this ultrarare disease.

Case Description: We update the clinical course and report new treatment outcomes of a 32-year-old man with ADP managed for many years with weekly prophylactic hemin infusions. He has developed evidence of iron overload and was more recently found to have compensated cirrhosis. The patient was started on givosiran (Givlaari™, Alnylam), a small interfering RNA (siRNA) therapeutic that is effective in preventing frequently recurring attacks of acute intermittent porphyria (AIP), the most common type of AHP.

Discussion: No adverse effects of givosiran on the liver were observed in this patient with cirrhosis during 6 months of treatment with givosiran. The patient has continued to have recurrent attacks, with transient decreases in ALA levels only as related to treatment of his attacks with hemin. Our experience limited to one patient with ADP suggests that givosiran may not be effective in this type of acute porphyria. Since ADP may have an erythropoietic component, treatment with hydroxyurea, which was beneficial in one previous case, is planned.

Novel treatment options for acute hepatic porphyrias

PURPOSE OF REVIEW

Acute hepatic porphyrias (AHP) are a group of rare diseases that are characterized by episodic acute neurovisceral pain episodes caused by abnormal accumulation of the neurotoxic porphyrin precursor delta-aminolevulinic acid (ALA). Patient with frequent recurrent acute attacks have been difficult to treat and these patients sometimes require liver transplantation. Recent developments in small interfering RNA (siRNA)-based therapy led to the development of an effective prophylactic treatment for patients with frequent recurrent attacks. This review will describe treatment options for AHP and highlight management in light of new treatment option.

RECENT FINDINGS

Givosiran is a novel siRNA-based therapy targeted specifically to hepatocytes to inhibit ALA synthase 1, the first and rate-limiting step in heme biosynthesis. Patients with frequent recurrent attacks treated with givosiran had durable normalization of ALA and significantly reduced numbers of acute attacks and need for hemin treatment. The overall safety profile for givosiran was comparable with placebo and the drug was recently approved by the Food and Drug Administration for treatment of AHP patients.

SUMMARY

Givosiran is an effective treatment for prevention of acute porphyria attacks in AHP patients with frequent recurrent attacks.

The acute hepatic porphyrias

The acute hepatic porphyrias (AHP) are a group of four inherited diseases of heme biosynthesis. They present with similar severe, episodic, acute neurovisceral symptoms due to abnormally elevated levels of porphyrin precursors delta-aminolevulinic acid (ALA). Recently genetic screening indicates that the prevalence of mutation carrier state is more common than previously thought, occurring in 1 in 1,500, though the clinical penetrance of symptomatic AHP is low at ~1%. Symptomatic attacks occur primarily in females during their reproductive years. In an acute porphyria attack, the primary symptom is abdominal pain, due to intestinal dysmotility from autonomic nerve injury. Other manifestations include seizures, weakness and mood changes, point to injury involving peripheral and central nervous system. Due to the non-specific nature of the symptoms and signs in AHP, the diagnosis is often delayed by many years. The diagnosis of AHP depends on biochemical evidence of elevated ALA and PBG levels in urine during symptomatic attacks. Genetic testing is used for confirmation of the gene involved and the exact mutation. Treatment involves administration of heme, which downregulates production of ALA. Long-term management centers on educating genetic carriers on avoiding triggers that increase the risk of acute attacks and screening family members.

Exploring human porphobilinogen synthase metalloprotein by quantum biochemistry and evolutionary methods

Previous studies have shown the porphobilinogen synthase (PBGS) zinc-binding mechanism and its conservation among the living cells. However, the precise molecular interaction of zinc with the active center of the enzyme is unknown. In particular, quantum chemistry techniques within the density functional theory (DFT) framework have been the key methodology to describe metalloproteins, when one is looking for a compromise between accuracy and computational feasibility. Considering this, we used DFT-based models within the molecular fractionation with conjugate caps scheme to evaluate the binding energy features of zinc interacting with the human PBGS. Besides, phylogenetic and clustering analyses were successfully employed in extracting useful information from protein sequences to identify groups of conserved residues that build the ions-binding site. Our results also report a conservative assessment of the relevant amino acids, as well as the benchmark analysis of the calculation models used. The most relevant intermolecular interactions in Zn2+-PBGS are due to the amino acids CYS0122, CYS0124, CYS0132, ASP0169, SER0168, ARG0221, HIS0131, ASP0120, GLY0133, VAL0121, ARG0209, and ARG0174. Among these residues, we highlighted ASP0120, GLY0133, HIS0131, SER0168, and ARG0209 by co-occurring in all clusters generated by unsupervised clustering analysis. On the other hand, the triple cysteines at 2.5 Å from zinc (CYS0122, CYS0124, and CYS0132) have the highest energy attraction and are absent in the taxa Viridiplantae, Sar, Rhodophyta, and some Bacteria. Additionally, the performance of the DFT-based models shows that the processing time-dependence is more associated with the choice of the basis set than the exchange-correlation functional.

Acute Intermittent Porphyria: An Overview of Therapy Developments and Future Perspectives Focusing on Stabilisation of HMBS and Proteostasis Regulators

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease with low clinical penetrance, caused by mutations in the hydroxymethylbilane synthase (HMBS) gene, which encodes the third enzyme in the haem biosynthesis pathway. In susceptible HMBS mutation carriers, triggering factors such as hormonal changes and commonly used drugs induce an overproduction and accumulation of toxic haem precursors in the liver. Clinically, this presents as acute attacks characterised by severe abdominal pain and a wide array of neurological and psychiatric symptoms, and, in the long-term setting, the development of primary liver cancer, hypertension and kidney failure. Treatment options are few, and therapies preventing the development of symptomatic disease and long-term complications are non-existent. Here, we provide an overview of the disorder and treatments already in use in clinical practice, in addition to other therapies under development or in the pipeline. We also introduce the pathomechanistic effects of HMBS mutations, and present and discuss emerging therapeutic options based on HMBS stabilisation and the regulation of proteostasis. These are novel mechanistic therapeutic approaches with the potential of prophylactic correction of the disease by totally or partially recovering the enzyme functionality. The present scenario appears promising for upcoming patient-tailored interventions in AIP.

Heme biosynthesis depends on previously unrecognized acquisition of iron-sulfur cofactors in human amino-levulinic acid dehydratase

Heme biosynthesis and iron-sulfur cluster (ISC) biogenesis are two major mammalian metabolic pathways that require iron. It has long been known that these two pathways interconnect, but the previously described interactions do not fully explain why heme biosynthesis depends on intact ISC biogenesis. Herein we identify a previously unrecognized connection between these two pathways through our discovery that human aminolevulinic acid dehydratase (ALAD), which catalyzes the second step of heme biosynthesis, is an Fe-S protein. We find that several highly conserved cysteines and an Ala306-Phe307-Arg308 motif of human ALAD are important for [Fe₄S₄] cluster acquisition and coordination. The enzymatic activity of human ALAD is greatly reduced upon loss of its Fe-S cluster, which results in reduced heme biosynthesis in human cells. As ALAD provides an early Fe-S-dependent checkpoint in the heme biosynthetic pathway, our findings help explain why heme biosynthesis depends on intact ISC biogenesis.

Heme biosynthesis depends on iron-sulfur (Fe-S) cluster biogenesis but the molecular connection between these pathways is not fully understood. Here, the authors show that the heme biosynthesis enzyme ALAD contains an Fe-S cluster, disruption of which reduces ALAD activity and heme production in human cells.

5-Aminolevulinate dehydratase porphyria: Update on hepatic 5-aminolevulinic acid synthase induction and long-term response to hemin

BACKGROUND

5-Aminolevulinic acid dehydratase (ALAD) porphyria (ADP) is an ultrarare autosomal recessive disease, with only eight documented cases, all of whom were males. Although classified as an acute hepatic porphyria (AHP), induction of the rate limiting hepatic enzyme 5-aminolevulinic acid synthase-1 (ALAS1) has not been demonstrated, and the marrow may also contribute excess 5-aminolevulinic acid (ALA). Two patients have died and reported follow up for the others is limited, so the natural history of this disease is poorly understood and treatment experience limited.

METHODS

We report new molecular findings and update the clinical course and treatment of the sixth reported ADP patient, now 31 years old and the only known case in the Americas, and review published data regarding genotype-phenotype correlation and treatment.

RESULTS

Circulating hepatic 5-aminolevulinic acid synthase-1 (ALAS1) mRNA was elevated in this case, as in other AHPs. Gain of function mutation of erythroid specific ALAS2 - an X-linked modifying gene in some other porphyrias - was not found. Seven reported ADP cases had compound heterozygous ALAD mutations resulting in very low residual ALAD activity and symptoms early in life or adolescence. One adult with a germline ALAD mutant allele developed ADP in association with a clonal myeloproliferative disorder, polycythemia vera.

CONCLUSIONS

Elevation in circulating hepatic ALAS1 and response to treatment with hemin indicate that the liver is an important source of excess ALA in ADP, although the marrow may also contribute. Intravenous hemin was effective in most reported cases for treatment and prevention of acute attacks of neurological symptoms.

Porphyric Neuropathy: Pathophysiology, Diagnosis, and Updated Management

PURPOSE OF REVIEW

To review the peripheral neurological complications of the acute hepatic porphyrias, as well as the latest advances in their pathophysiology and management.

RECENT FINDINGS

The diagnosis of porphyric neuropathy remains challenging as varying neuropathic patterns are encountered depending on disease stage, including a non-length-dependent distribution pattern. The major pathophysiologic mechanism is δ-aminolevulinic acid (ALA)-induced neurotoxicity. The less restrictive blood-nerve barrier in the autonomic ganglia and myenteric plexus may explain the frequency of dysautonomic manifestations. Recently, a prophylactic small interfering RNA (siRNA)-based therapy that reduces hepatic ALA Synthase-1 mRNA was approved for patients with recurrent neuro-visceral attacks. Neurologists should appreciate the varying patterns of porphyric neuropathy. As with most toxin-induced axonopathies, long-term outcomes depend on early diagnosis and treatment. While the short-term clinical and biochemical benefits of siRNA-based therapy are known, its long-term effects on motor recovery, chronic pain, and dysautonomic manifestations are yet to be determined.

Heme biosynthesis and the porphyrias

Porphyrias, is a general term for a group of metabolic diseases that are genetic in nature. In each specific porphyria the activity of specific enzymes in the heme biosynthetic pathway is defective and leads to accumulation of pathway intermediates. Phenotypically, each disease leads to either neurologic and/or photocutaneous symptoms based on the metabolic intermediate that accumulates. In each porphyria the distinct patterns of these substances in plasma, erythrocytes, urine and feces are the basis for diagnostically defining the metabolic defect underlying the clinical observations. Porphyrias may also be classified as either erythropoietic or hepatic, depending on the principal site of accumulation of pathway intermediates. The erythropoietic porphyrias are congenital erythropoietic porphyria (CEP), and erythropoietic protoporphyria (EPP). The acute hepatic porphyrias include ALA dehydratase deficiency porphyria, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP) and variegate porphyria (VP). Porphyria cutanea tarda (PCT) is the only porphyria that has both genetic and/or environmental factors that lead to reduced activity of uroporphyrinogen decarboxylase in the liver. Each of the 8 enzymes in the heme biosynthetic pathway have been associated with a specific porphyria (Table 1). Mutations affecting the erythroid form of ALA synthase (ALAS2) are most commonly associated with X-linked sideroblastic anemia, however, gain-of-function mutations of ALAS2 have also been associated with a variant form of EPP. This overview does not describe the full clinical spectrum of the porphyrias, but is meant to be an overview of the biochemical steps that are required to make heme in both erythroid and non-erythroid cells.

Acute hepatic porphyrias: Current diagnosis & management

Each of the four acute hepatic porphyrias is due to mutation of an enzyme in the heme biosynthetic pathway. The accumulation of pathway intermediates that occur most notably when these diseases are active is the basis for screening and establishing a biochemical diagnosis of these rare disorders. Measurement of enzyme activities and especially DNA testing also are important for diagnosis. Suspicion of the diagnosis and specific testing, particularly measurement of urinary porphobilinogen, are often delayed because the symptoms are nonspecific, even when severe. Urinary porphyrins are also measured, but their elevation is much less specific. If porphobilinogen is elevated, second line testing will establish the type of acute porphyria. DNA testing identifies the familial mutation and enables screening of family members. Management includes removal of triggering factors whenever possible. Intravenous hemin is the most effective treatment for acute attacks. Carbohydrate loading is sometimes used for mild attacks. Cyclic attacks, if frequent, can be prevented by a GnRH analogue. Frequent noncyclic attacks are sometime preventable by scheduled (e.g. weekly) hemin infusions. Long term complications may include chronic pain, renal impairment and liver cancer. Other treatments, including RNA interference, are under development.

Current and innovative emerging therapies for porphyrias with hepatic involvement

Porphyrias are rare inherited disorders caused by specific enzyme dysfunctions in the haem synthesis pathway, which result in abnormal accumulation of specific pathway intermediates. The symptoms depend upon the chemical characteristics of these substances. Porphyrins are photoreactive and cause photocutaneous lesions on sunlight-exposed areas, whereas accumulation of porphyrin precursors is related to acute neurovisceral attacks. Current therapies are suboptimal and mostly address symptoms rather than underlying disease mechanisms. Advances in the understanding of the molecular bases and pathogenesis of porphyrias have paved the way for the development of new therapeutic strategies. In this Clinical Trial Watch we summarise the basic principles of these emerging approaches and what is currently known about their application to porphyrias of hepatic origin or with hepatic involvement.

Clinical Guide and Update on Porphyrias

Physicians should be aware of porphyrias, which could be responsible for unexplained gastrointestinal, neurologic, or skin disorders. Despite their relative rarity and complexity, most porphyrias can be easily defined and diagnosed. They are caused by well-characterized enzyme defects in the complex heme biosynthetic pathway and are divided into categories of acute vs non-acute or hepatic vs erythropoietic porphyrias. Acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and aminolevulinic acid dehydratase deficient porphyria) manifest in attacks and are characterized by overproduction of porphyrin precursors, producing often serious abdominal, psychiatric, neurologic, or cardiovascular symptoms. Patients with variegate porphyria and hereditary coproporphyria can present with skin photosensitivity. Diagnosis relies on measurement of increased urinary 5-aminolevulinic acid (in patients with aminolevulinic acid dehydratase deficient porphyria) or increased 5-aminolevulinic acid and porphobilinogen (in patients with other acute porphyrias). Management of attacks requires intensive care, strict avoidance of porphyrinogenic drugs and other precipitating factors, caloric support, and often heme therapy. The non-acute porphyrias are porphyria cutanea tarda, erythropoietic protoporphyria, X-linked protoporphyria, and the rare congenital erythropoietic porphyria. They lead to the accumulation of porphyrins that cause skin photosensitivity and occasionally severe liver damage. Secondary elevated urinary or blood porphyrins can occur in patients without porphyria, for example, in liver diseases, or iron deficiency. Increases in porphyrin precursors and porphyrins are also found in patients with lead intoxication. Patients with porphyria cutanea tarda benefit from iron depletion, hydroxychloroquine therapy, and, if applicable, elimination of the hepatitis C virus. An α-melanocyte-stimulating hormone analogue can reduce sunlight sensitivity in patients with erythropoietic protoporphyria or X-linked protoporphyria. Strategies to address dysregulated or dysfunctional steps within the heme biosynthetic pathway are in development.

Evaluation of hematological, biochemical parameters and thiol enzyme activity in chrome plating workers

The most commonly used solution in chrome plating bath is chromic acid (hexavalent Cr), and a considerable amount of mists is released into the air and consequently produce hazards to workers. Thus, the aim of this study was to evaluate whether the biomarker of exposure to metals, specially Cr levels, presents associations with hematological and biochemical parameters and if they can alter the activity of enzymes that contain thiol groups such as pyruvate kinase, creatine kinase, adenylate kinase, and δ-aminolevulinate dehydratase. Fifty male chrome plating workers were used for exposed group and 50 male non-exposed workers for control group. For that, biological monitoring was performed through quantification of metals on total blood and urine by inductively coupled plasma mass spectrometry (ICP-MS) and enzyme activity was performed by spectrometry in erythrocytes. In addition, chromium levels in water was quantified and ecotoxicology assay was performed with Allium cepa test. The results demonstrated that blood and urinary chromium levels in exposed group were higher than the control group (p < 0.0001). Furthermore, decreased activity of enzymes was found in those that contain thiol groups from exposed group when compared with the control group (p < 0.001). The water analysis did not present a statistical difference between control and exposed groups (p > 0.05), demonstrating that water did not seem to be the source of contamination. In summary, our findings indicated some toxicology effects observed in the exposed group, such as thiol enzyme inhibition, mainly associated with occupational exposure in chrome plating and besides the presence of other metals, and Cr demonstrated to influence the activity of the enzymes analyzed in this research.

Hepatic porphyria: A narrative review

Porphyrias are a group of metabolic disorders, which result from a specific abnormality in one of the eight enzymes of the heme biosynthetic pathway. These have been subdivided based on the predominant site of enzyme defect into hepatic and erythropoietic types and based on clinical presentation into acute neurovisceral and cutaneous blistering porphyrias. This review focuses on hepatic porphyrias, which include acute intermittent porphyria (AIP), variegate porphyria (VP), hereditary coproporphyria (HCP), aminolevulinic acid dehydratase deficiency porphyria (ADP), and porphyria cutanea tarda (PCT). Of these, AIP and ADP are classified as acute porphyria, PCT as cutaneous, while VP and HCP present with both acute and cutaneous clinical manifestations. Porphobilinogen levels in a spot urine sample is the initial screening test for the diagnosis of acute hepatic porphyria, and plasma with spot urine porphyrin levels is the initial screening test to approach patients suspected of cutaneous porphyria. Specific biochemical porphyrin profile for each porphyria helps in determining the specific diagnosis. Pain relief and elimination of triggering agents are the initial steps in managing a patient presenting with an acute attack. Intravenous glucose administration terminates the mild episode of acute porphyria, with intravenous hemin needed for management of moderate to severe episodes. Liver transplantation is curative and may be needed for patients with a life-threatening acute porphyria attack or for patients with recurrent acute attacks refractory to prophylactic treatment. Of the cutaneous porphyrias, PCT is the most common and is frequently associated with a combination of multiple susceptibility factors such as alcohol use, smoking, hepatitis C virus infection, HIV infection, estrogen use, and mutations of the hemochromatosis gene. Regular phlebotomy schedule and low-dose hydroxychloroquine are effective and safe treatment options for management of PCT.

Porphyria Diagnostics-Part 1: A Brief Overview of the Porphyrias

Porphyria diseases are a group of metabolic disorders caused by abnormal functioning of heme biosynthesis enzymes and characterized by excessive accumulation and excretion of porphyrins and their precursors. Precisely which of these chemicals builds up depends on the type of porphyria. Porphyria is not a single disease but a group of nine disorders: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), variegate porphyria (VP), δ-aminolevulinic acid dehydratase deficiency porphyria (ADP), porphyria cutanea tarda (PCT), hepatoerythropoietic porphyria (HEP), congenital erythropoietic porphyria (CEP), erythropoietic protoporphyria (EPP), and X-linked protoporphyria (XLP). Each porphyria results from overproduction of heme precursors secondary to partial deficiency or, in XLP, increased activity of one of the enzymes of heme biosynthesis. Taken together, all forms of porphyria afflict fewer than 200,000 people in the United States. Based on European studies, the most common porphyria, PCT, has a prevalence of 1 in 10,000, the most common acute porphyria, AlP, has a prevalence of ∼1 in 20,000, and the most common erythropoietic porphyria, EPP, is estimated at 1 in 50,000 to 75,000. CEP is extremely rare, with prevalence estimates of 1 in 1,000,000 or less. Only six cases of ADP are documented. The current porphyria literature is very exhaustive and a brief overview of porphyria diseases is essential in order for the reader to better appreciate the relevance of this area of research prior to undertaking biochemical diagnostics procedures. This unit summarizes the current knowledge on the classification, clinical features, etiology, pathogenesis, and genetics of porphyria diseases.

Acute porphyrias in the USA: features of 108 subjects from porphyrias consortium

BACKGROUND

Recent descriptions of the clinical and laboratory features of subjects with acute porphyrias in the US are lacking. Our aim was to describe clinical, biochemical, and genetic features of 108 subjects.

METHODS

Between September 2010 and December 2012, 108 subjects with acute porphyrias (90 acute intermittent porphyrias, 9 hereditary coproporphyrias, 9 variegate porphyrias) were enrolled into an observational study. Genetic testing was performed at a central genetic testing laboratory and clinical information entered into a central database. Selected features were compared with data for adults in the US.

RESULTS

Most subjects (88/108, 81%) were female, with self-reported onset of symptoms in the second through fourth decades of life. The most common symptom was abdominal pain. Appendectomies and cholecystectomies were common before a diagnosis of porphyria. The diagnosis was delayed by a mean of 15 years. Anxiety and depression were common, and 18% complained of chronic symptoms, especially neuropathic and other pains. The incidences of systemic arterial hypertension, chronic kidney disease, seizure disorders, and psychiatric conditions were markedly increased. Mutations of the known causative genes were found in 102/105 of those tested, with novel mutations being found in 37, including in 7/8 subjects with hereditary coproporphyria. Therapy with intravenous hematin was the most effective therapy both for treatment of acute attacks and for prevention of recurrent attacks.

CONCLUSIONS

Acute porphyrias often remain undiagnosed for more than a decade after first symptoms develop. Intravenous hematin is the treatment of choice, both for treatment of acute attacks and for prevention of recurrent attacks.

Liver transplantation in the management of porphyria

Porphyrias are a group of eight metabolic disorders, each resulting from a mutation that affects an enzyme of the heme biosynthetic pathway. Porphyrias are classified as hepatic or erythropoietic, depending upon the site where the gene defect is predominantly expressed. Clinical phenotypes are classified as follows: (1) acute porphyrias with neurovisceral symptoms: acute intermittent porphyria; delta amino-levulinic acid hydratase deficiency porphyria; hereditary coproporphyria; and variegate porphyria and (2) cutaneous porphyrias with skin blistering and photosensitivity: porphyria cutanea tarda; congenital erythropoietic porphyria; hepatoerythropoietic porphyria and both erythropoietic protoporphyrias: autosomal dominant and X-linked. Liver transplantation (LT) may be needed for recurrent and/or life-threatening acute attack in acute intermittent porphyria or acute liver failure or end-stage chronic liver disease in erythropoietic protoporphyria. LT in acute intermittent porphyria is curative. Erythropoietic protoporphyria patients needing LT should be considered for bone marrow transplantation to achieve cure.

CONCLUSION

This article provides an overview of porphyria with diagnostic approaches and management strategies for specific porphyrias and recommendations for LT with indications, pretransplant evaluation, and posttransplant management.

Role of genetic testing in the management of patients with inherited porphyria and their families

The porphyrias are a group of mainly inherited metabolic conditions that result from partial deficiency of individual enzymes in the haem biosynthesis pathway. Clinical presentation is either with acute neurovisceral attacks, skin photosensitivity or both, and is due to overproduction of pathway intermediates. The primary diagnosis in the proband is based on biochemical testing of appropriate samples, preferably during or soon after onset of symptoms. The role of genetic testing in the autosomal dominant acute porphyrias (acute intermittent porphyria, hereditary coproporphyria and variegate porphyria) is to identify presymptomatic carriers of the family specific pathogenic mutation so that they can be counselled on how to minimize their risk of suffering an acute attack. At present the additional genetic factors that influence penetrance are not known, and all patients are treated as equally at risk. Genetic testing in the erythropoietic porphyrias (erythropoietic protoporphyria, congenital erythropoietic porphyria and X-linked dominant protoporphyria) is focused on predictive and preconceptual counselling, prenatal testing and genotype-phenotype correlation. Recent advances in analytical technology have resulted in increased sensitivity of mutation detection with success rates of greater than 90% for most of the genes. The ethical and consent issues are discussed. Current research into genetic factors that affect penetrance is likely to lead to a more refined approach to counselling for presymptomatic gene carriers.

Porphyric neuropathy

Porphyric neuropathy often poses a diagnostic dilemma; it is typically associated with the hepatic porphyrias, characterized by acute life-threatening attacks of neurovisceral symptoms that mimic a range of acute medical and psychiatric conditions. The development of acute neurovisceral attacks is responsive to environmental factors, including drugs, hormones, and diet. This chapter reviews the clinical manifestations, genetics, pathophysiology, and mechanisms of neurotoxicity of the acute hepatic porphyrias. While the etiology of the neurological manifestations in the acute porphyrias remains undefined, the main hypotheses include toxicity of porphyrin precursors and deficiency of heme synthesis. These hypotheses will be discussed with reference to novel experimental models of porphyric neuropathy.

Direct assay of delta-aminolevulinic acid dehydratase in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry

We report a new assay of human delta-aminolevulinic acid dehydratase (ALAD), an enzyme converting delta-aminolevulinic acid (ALA) into porphobilinogen. The assay is developed for use in the clinical diagnosis of delta-aminolevulinic acid dehydratase-deficient porphyria, a rare enzymatic deficiency of the heme biosynthetic pathway. The assay involves the incubation of erythrocyte lysate with the natural substrate, ALA, followed by quantitative in situ conversion of porphobilinogen to its butyramide, and liquid-liquid extraction into a mass spectrometer-friendly solvent. Quantitation of the butyrylated porphobilinogen is done by electrospray ionization tandem mass spectrometry, using a deuterium labeled internal standard. The assay stays well within the range wherein ALAD activity is linear with time. The K(m) of ALAD for ALA was measured as 333 microM, and the V(max) was 19.3 microM/h. Average enzyme activity among a random sample of 36 anonymous individuals was 277 micromol/L erythrocyte lysate/hour with a standard deviation of 90 micromol/L erythrocyte lysate/hour. The tandem mass spectrometric assay should easily detect the enzyme deficiency, which causes a reduction of activity by 95-99%. The assay shows good reproducibility and low background, requires a simple workup, and uses a commercially available substrate.

Co-synthesis of Human delta-Aminolevulinate Dehydratase (ALAD) Mutants with the Wild-type Enzyme in Cell-free System-Critical Importance of Conformation on Enzyme Activity-

Properties of mutant delta-aminolevulinate dehydratase (ALAD) found in patients with ALAD porphyria were studied by enzymological and immunological analyses after the synthesis of enzyme complexes using a cell-free system. Enzyme activities of homozygous G133R, K59N/G133R, V153M, and E89K mutants were 11%, 22%, 67%, and 75% of the wild-type ALAD, respectively, whereas that of K59N, a normal variant, was 112%. Enzyme activities of L273R, C132R and F12L were undetectable. Co-synthesis of F12L, L273R, G133R, K59N/G133R, or C132R mutants with the wild-type at various ratios showed that ALAD activity was proportionally decreased in the amount of the wild-type in the complex. In contrast, co-synthesis of V153M, K59N, and E89K with the wild-type did not influence enzyme activity of the wild-type. Surface charge changes in K59N, E89K, C132R and G133R predicted by mutations were also confirmed by native polyacrylamide gel electrophoresis. A compound E89K and C132R complex showed ALAD activity similar to that was found in erythrocytes of the patient. These findings indicate that cell-free synthesis of ALAD proteins reflects enzymatic activities found in patients, and suggest that, in addition to the direct effect of mutations on the catalytic activity, conformational effects play an important role in determining enzyme activity.

ALAD porphyria is a conformational disease

ALAD porphyria is a rare porphyric disorder, with five documented compound heterozygous patients, and it is caused by a profound lack of porphobilinogen synthase (PBGS) activity. PBGS, also called "delta-aminolevulinate dehydratase," is encoded by the ALAD gene and catalyzes the second step in the biosynthesis of heme. ALAD porphyria is a recessive disorder; there are two common variant ALAD alleles, which encode K59 and N59, and eight known porphyria-associated ALAD mutations, which encode F12L, E89K, C132R, G133R, V153M, R240W, A274T, and V275M. Human PBGS exists as an equilibrium of functionally distinct quaternary structure assemblies, known as "morpheeins," in which one functional homo-oligomer can dissociate, change conformation, and reassociate into a different oligomer. In the case of human PBGS, the two assemblies are a high-activity octamer and a low-activity hexamer. The current study quantifies the morpheein forms of human PBGS for the common and porphyria-associated variants. Heterologous expression in Escherichia coli, followed by separation of the octameric and hexameric assemblies on an ion-exchange column, showed that the percentage of hexamer for F12L (100%), R240W (80%), G133R (48%), C132R (36%), E89K (31%), and A274T (14%) was appreciably larger than for the wild-type proteins K59 and N59 (0% and 3%, respectively). All eight porphyria-associated variants, including V153M and V275M, showed an increased propensity to form the hexamer, according to a kinetic analysis. Thus, all porphyria-associated human PBGS variants are found to shift the morpheein equilibrium for PBGS toward the less active hexamer. We propose that the disequilibrium of morpheein assemblies broadens the definition of conformational diseases beyond the prion disorders and that ALAD porphyria is the first example of a morpheein-based conformational disease.

Modern diagnosis and management of the porphyrias

Recent advances in the molecular understanding of the porphyrias now offer specific diagnosis and precise definition of the types of genetic mutations involved in the disease. Molecular diagnostic testing is powerful and very useful in kindred evaluation and genetic counselling when a disease-responsible mutation has been identified in the family. It is also the only way to properly screen asymptomatic gene carriers, facilitating correct treatment and appropriate genetic counselling of family members at risk. However, it should be noted that DNA-based testing is for the diagnosis of the gene carrier status, but not for the diagnosis of clinical syndrome or severity of the disease, e.g. an acute attack. For the diagnosis of clinically expressed porphyrias, a logical stepwise approach including the analysis of porphyrins and their precursors should not be underestimated, as it is still very useful, and is often the best from the cost-effective point of view.