The Porphyrias.

The porphyrias are clinically variable and genetically heterogeneous, predominantly hereditary metabolic diseases, which are caused by a dysfunction of specific enzymes in heme biosynthesis. Here, we provide an overview of the etiopathogenesis, clinic, differential diagnosis, laboratory diagnostics and therapy of these complex metabolic disorders and cover in detail the most common form of porphyria worldwide (porphyria cutanea tarda), the most frequent childhood porphyria (erythropoietic protoporphyria), and the most common neurocutaneous porphyria (variegate porphyria).

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.

Recent advances on porphyria genetics: Inheritance, penetrance & molecular heterogeneity, including new modifying/causative genes.

The inborn errors of heme biosynthesis, the Porphyrias, include eight major disorders resulting from loss-of-function (LOF) or gain-of-function (GOF) mutations in eight of the nine heme biosynthetic genes. The major sites of heme biosynthesis are the liver and erythron, and the underlying pathophysiology of each of these disorders depends on the unique biochemistry, cell biology, and genetic mechanisms in these tissues. The porphyrias are classified into three major categories: 1) the acute hepatic porphyrias (AHPs), including Acute Intermittent Porphyria (AIP), Hereditary Coproporphyria (HCP), Variegate Porphyria (VP), and 5-Aminolevlulinic Acid Dehydratase Deficient Porphyria (ADP); 2) a hepatic cutaneous porphyria, Porphyria Cutanea Tarda (PCT); and 3) the cutaneous erythropoietic porphyrias, Congenital Erythropoietic Porphyria (CEP), Erythropoietic Protoporphyria (EPP), and X-Linked Protoporphyria (XLP). Their modes of inheritance include autosomal dominant with markedly decreased penetrance (AIP, VP, and HCP), autosomal recessive (ADP, CEP, and EPP), or X-linked (XLP), as well as an acquired sporadic form (PCT). There are severe homozygous dominant forms of the three AHPs. For each porphyria, its phenotype, inheritance pattern, unique genetic principles, and molecular genetic heterogeneity are presented. To date, >1000 mutations in the heme biosynthetic genes causing their respective porphyrias have been reported, including low expression alleles and genotype/phenotype correlations that predict severity for certain porphyrias. The tissue-specific regulation of heme biosynthesis and the unique genetic mechanisms for each porphyria are highlighted.

[The cutaneous porphyrias]. / Porphyries cutanées.

The porphyrias are a group of metabolic disorders resulting from an innate abnormality in haem biosynthesis, and the clinical settings of which vary according to the genetic enzyme abnormality in question. These are genetic disorders with autosomal dominant or recessive inheritance of varying penetrance, and whose clinical expression differs according to the preferential location of haem precursors. Different classifications have been proposed according to genetic inheritance, the enzyme anomaly at issue, and clinical expression. The clinical classification distinguishes between acute porphyria (acute intermittent porphyria, porphyria variegata, hereditary coproporphyria), bullous cutaneous porphyrias (porphyria cutanea tarda, porphyria variegata and hereditary coproporphyria), painful photosensitive acute cutaneous porphyrias (erythropoietic protoporphyria and X-linked dominant protoporphyria), and rare recessive porphyrias (congenital erythropoietic porphyria, Doss porphyria, hepatoerythropoietic porphyria and harderoporphyria). Treatment depends on the clinical expression of the disorder.

[The laboratory diagnostics of disorders of porphyrin metabolism: a lecture].

The lecture presents data concerning biosynthesis of haem and mechanisms of its regulation in bone marrow and liver. The basic pathogenic mechanisms of porphyrias development and their classification are exposed. The optimal list of laboratory tests to diagnose porphyrias is presented. The role and significance of various laboratory analysis techniques to diagnose porphyrias are demonstrated. The technology of laboratory analysis in case of porphyria suspicion is described.

Porphyrias.

Hereditary porphyrias are a group of eight metabolic disorders of the haem biosynthesis pathway that are characterised by acute neurovisceral symptoms, skin lesions, or both. Every porphyria is caused by abnormal function of a separate enzymatic step, resulting in a specific accumulation of haem precursors. Seven porphyrias are the result of a partial enzyme deficiency, and a gain of function mechanism has been characterised in a new porphyria. Acute porphyrias present with acute attacks, typically consisting of severe abdominal pain, nausea, constipation, confusion, and seizure, and can be life-threatening. Cutaneous porphyrias present with either acute painful photosensitivity or skin fragility and blisters. Rare recessive porphyrias usually manifest in early childhood with either severe cutaneous photosensitivity and chronic haemolysis or chronic neurological symptoms with or without photosensitivity. Porphyrias are still underdiagnosed, but when they are suspected, and dependent on clinical presentation, simple first-line tests can be used to establish the diagnosis in all symptomatic patients. Diagnosis is essential to enable specific treatments to be started as soon as possible. Screening of families to identify presymptomatic carriers is crucial to decrease risk of overt disease of acute porphyrias through counselling about avoidance of potential precipitants.

[Oxidative stress in porphyria and carriers].

UNLABELLED: We sought to establish a causal relationship between oxidative stress and porphyria in patients and carriers. We reported changes in urinary porphyrin concentrations related to 8-hydroxy-2'-deoxyguanosine. METHODS: We measured urinary 8-hydroxy-2'-deoxyguanosine concentration in porphyria patients and carriers with multifactorial inheritance as a possible marker of attack. The porphyria types included 10 patients with porphyria cutanea tarda, 5 with variegate porphyria, 8 with hereditary coproporphyria, 7 with congenital erythropoietic porphyria, 5 with erythropoietic protoporphyria, 5 with acute intermittent porphyria, 7 erythropoietic protoporphyria carriers, and 7 acute intermittent porphyria carriers. RESULTS: Urinary porphyrin concentrations in these patients were significantly higher than those in healthy subjects (p<0.001). Urinary 8-hydroxy-2'-deoxyguanosine concentrations were significantly high in dermatopathy porphyria types namely porphyria cutanea tarda (p<0.001), variegate porphyria (p<0.05), hereditary coproporphyria (p<0.05), congenital erythropoietic phyria (p<0.05), and erythropoietic protoporphyria (p<0.001). CONCLUSION: These results reveal that urinary 8-hydroxy-2'-deoxyguanosine concentration in cutis porphyria types is a good predictor of attack and abatement.

Porphyrias and photosensitivity: pathophysiology for the clinician.

Porphyrias are disorders caused by defects in the biosynthetic pathway of heme. Their manifestations can be divided into three distinct syndromes, each attributable to the accumulation of three distinct classes of molecules. The acute neurovisceral syndrome is caused by the accumulation of the neurotoxic porphyrin precursors, delta aminolevulinic acid, and porphobilinogen; the syndrome of immediate painful photosensitivity is caused by the lipid-soluble protoporphyrin IX and, the syndrome of delayed blistering photosensitivity, caused by the water-soluble porphyrins, uroporphyrin, and coproporphyrin. Porphyrias can manifest with one, or with a combination, of these syndromes, depending on whether one or more types of molecules are being accumulated. Iron plays a significant role in some of these conditions, as evidenced by improvements in both clinical manifestations and laboratory parameters, following iron depletion in porphyria cutanea tarda, or iron administration in some cases of X-linked erythropoietic protoporphyria. While the pathophysiology of a specific type of porphyrias, the protoporphyrias, appears to favor the administration of zinc, results so far have been conflicting, necessitating further studies in order to assess its potential benefit. The pathways involved in each disease, as well as insights into their pathobiological processes are presented, with an emphasis on the development of photosensitivity reactions.

Best practice guidelines on first-line laboratory testing for porphyria.

The porphyrias are disorders of haem biosynthesis which present with acute neurovisceral attacks or disorders of sun-exposed skin. Acute attacks occur mainly in adults and comprise severe abdominal pain, nausea, vomiting, autonomic disturbance, central nervous system involvement and peripheral motor neuropathy. Cutaneous porphyrias can be acute or chronic presenting at various ages. Timely diagnosis depends on clinical suspicion leading to referral of appropriate samples for screening by reliable biochemical methods. All samples should be protected from light. Investigation for an acute attack: • Porphobilinogen (PBG) quantitation in a random urine sample collected during symptoms. Urine concentration must be assessed by measuring creatinine, and a repeat requested if urine creatinine <2 mmol/L. • Urgent porphobilinogen testing should be available within 24 h of sample receipt at the local laboratory. Urine porphyrin excretion (TUP) should subsequently be measured on this urine. • Urine porphobilinogen should be measured using a validated quantitative ion-exchange resin-based method or LC-MS. • Increased urine porphobilinogen excretion requires confirmatory testing and clinical advice from the National Acute Porphyria Service. • Identification of individual acute porphyrias requires analysis of urine, plasma and faecal porphyrins. Investigation for cutaneous porphyria: • An EDTA blood sample for plasma porphyrin fluorescence emission spectroscopy and random urine sample for TUP. • Whole blood for porphyrin analysis is essential to identify protoporphyria. • Faeces need only be collected, if first-line tests are positive or if clinical symptoms persist. Investigation for latent porphyria or family history: • Contact a specialist porphyria laboratory for advice. Clinical, family details are usually required.

The porphyrias: clinical presentation, diagnosis and treatment.

The porphyrias comprise a clinically and genetically heterogeneous group of diseases mostly arising from a genetically determined dysfunction of specific enzymes along the pathway of heme biosynthesis. Based on the occurrence or absence of cutaneous symptoms and life-threatening acute neurological attacks, the different types of porphyrias can either be classified into cutaneous and non-cutaneous forms or acute and non-acute forms. Establishing an accurate diagnosis might be difficult for two reasons: i) the porphyrias can manifest with a broad but unspecific spectrum of clinical symptoms mimicking several other disorders, and ii) biochemical examination of urine, feces, and blood can reveal overlapping findings. Fortunately, however, the advances in the fields of molecular genetics during recent years have provided us with the possibility of overcoming these diagnostic pitfalls. Therefore, in controversial cases the correct diagnosis can finally be made using molecular biological techniques. Due to the various facets of the porphyrias, diagnosis and treatment should always imply a close interdisciplinary collaboration to counsel and help patients and their families most efficiently.

The porphyrias.

The porphyrias are a group of disorders involving enzymatic defects in heme synthesis. The porphyrias classically manifest neuro-visceral or photocutaneous symptoms based on which enzyme in the heme metabolic pathway is deficient. Although rare, the porphyrias would most likely be encountered in the emergency department in patients presenting with chronic unspecified abdominal or musculoskeletal pain and those with new onset of psychiatric complaints.

Porphyria: Pathophysiology, diagnosis, and treatment.

Porphyrias are inherited metabolic disorders that involve alterations in enzymes utilized in the heme biosynthetic pathway. Most of these conditions are inherited; however, some are believed to be acquired through environmental exposures. Patients with porhyrias often present with a wide range of clinical symptoms, making it difficult to diagnose. Treatments vary depending on clinical presentation. A thorough and detailed history is essential and key to discovering a porphyria diagnosis.

Porphyrias: A 2015 update.

The hereditary porphyrias comprise a group of eight metabolic disorders of the heme biosynthesis pathway. Each porphyria is caused by abnormal function at a separate enzymatic step resulting in a specific accumulation of heme precursors. Porphyrias are classified as hepatic or erythropoietic, based on the organ system in which heme precursors (δ-aminolevulinic acid [ALA], porphobilinogen and porphyrins) are overproduced. Clinically, porphyrias are characterized by acute neurovisceral symptoms, skin lesions or both. However, most if not all the porphyrias impair hepatic or gastrointestinal function. Acute hepatic porphyrias present with severe abdominal pain, nausea, constipation, confusion and seizure, which may be life threatening, and patients are at risk of hepatocellular carcinoma without cirrhosis. Porphyria Cutanea presents with skin fragility and blisters, and patients are at risk of hepatocellular carcinoma with liver iron overload. Erythropoietic protoporphyria and X-linked protoporphyria present with acute painful photosensitivity, and patients are at risk of acute liver failure. Altogether, porphyrias are still underdiagnosed, but once they are suspected, early diagnosis based on measurement of biochemical metabolites that accumulate in the blood, urine, or feces is essential so specific treatment can be started as soon as possible and long-term liver complications are prevented. Screening families to identify presymptomatic carriers is also crucial to prevent overt disease and chronic hepatic complications.

The porphyrias.

The porphyrias are a group of metabolic disorders arising from defects in the haem biosynthetic pathway. Most forms are inherited as Mendelian autosomal dominant characters, but some are recessive and others acquired. There is a linked group of diseases, which are not porphyrias, but have in common alterations of haem biosynthesis. The haem biosynthetic pathway is now well understood and the molecular biology of its function and dysfunction in the porphyrias is currently an area of major investigation. The acute porphyrias are of most importance since attacks of these may be life-threatening. A variety of factors may precipitate these attacks including various drugs, alcohol, strict dieting or fasting and hormonal fluctuations. The non-acute porphyrias are largely dermatological conditions, which present clinically as cutaneous photosensitivity. The dermatological changes are brought about by the photosensitizing properties of circulating porphyrins. On the basis of this photoactivity, porphyrins are now being used, therapeutically, in the treatment of cancer.

Nalidixic acid-induced photosensitivity in mice: a model for pseudoporphyria.

Porphyria cutanea tarda (PCT)-like photosensitivity eruptions have occurred in patients treated with nalidixic acid, furosemide (Lasix), or tetracycline. An animal model for nalidixic acid photosensitivity was developed in young CF-1 female mice. The hair on the back was plucked from groups of animals that were injected i.p. each day with nalidixic acid or saline. The animals were exposed to black-lamp radiation for 12 h daily for 6 weeks, followed by a 2-week rest period, and then 4 more weeks of UV radiation exposure. The nalidixic acid-treated animals developed far greater gross and chronic inflammatory changes than the saline-treated animals; microscopically and ultrastructurally they showed blister formation beneath the basal lamina at the same level as that found in PCT. This model appears to be suitable for the study of PCT-like and other photosensitivity reactions.

Discovery of a group I intron in the SSU rDNA of Ploeotia costata (Euglenozoa).

The gene coding for the small ribosomal subunit RNA of Ploeotia costata contains an actively splicing group I intron (Pco.S516) which is unique among euglenozoans. Secondary structure predictions indicate that paired segments P1-P10 as well as several conserved elements typical of group I introns and of subclass IC1 in particular are present. Phylogenetic analyses of SSU rDNA sequences demonstrate a well-supported placement of Ploeotia costata within the Euglenozoa; whereas, analyses of intron data sets uncover a close phylogenetic relation of Pco.S516 to S-516 introns from Acanthamoeba, Aureoumbra lagunensis (Stramenopila) and red algae of the order Bangiales. Discrepancies between SSU rDNA and intron phylogenies suggest horizontal spread of the group I intron. Monophyly of IC1 516 introns from Ploeotia costata, A. lagunensis and rhodophytes is supported by a unique secondary structure element: helix P5b possesses an insertion of 19 nt length with a highly conserved tetraloop which is supposed to take part in tertiary interactions. Neither functional nor degenerated ORFs coding for homing endonucleases can be identified in Pco.S516. Nevertheless, degenerated ORFs with His-Cys box motifs in closely related intron sequences indicate that homing may have occurred during evolution of the investigated intron group.

Acute porphyrias: diagnosis and management.

To summarize recent information about acute porphyrias and to provide clinicians with a practical diagnostic and management approach, we reviewed the pertinent literature and our clinical experience. The acute porphyrias are characterized by recurrent attacks of abdominal pain with or without additional manifestations of autonomic dysfunction or neuropsychiatric symptoms. On the basis of the potential of these disorders to affect the skin, they are further subdivided into neuroporphyrias and neurocutaneous porphyrias. During acute attacks, acute porphyria is always associated with increased levels of urinary porphyrin precursors. Between attacks, patients with neurocutaneous porphyrias may have normal urinary porphyrins; therefore, stool porphyrins, which are invariably increased, are the most helpful. Latent disease can be detected by the measurement of either urinary and stool porphyrins or cellular enzyme activity. Specific intravenous therapy with hematin has resulted in biochemical remissions, but its clinical benefit remains controversial. Measurement of urinary and stool porphyrins or porphyrin precursors is critical for the diagnosis of clinically overt acute porphyria. Enzyme assays are helpful in supporting the diagnosis but are best used to identify family members with latent disease. Preventive measures and supportive therapy are the mainstays of current management of patients with porphyria.

Enzyme heterogeneity in the porphyrias.

The use of immunological methods for measuring enzyme mass has identified several varieties of porphyria in which the reduction of porphyrin enzyme activity is not accompanied by a corresponding change in the enzyme mass. Currently, acute intermittent porphyria and hepatoerythropoietic porphyria have exhibited this phenomenon. In porphyria cutanea tarda, it has recently been shown that the pattern of enzyme deficiency in erythrocytic and nonerythrocytic tissues does not strictly follow the inheritance pattern (familial and sporadic) previously described. Also, contrary to previous dogma, some cases of type 1 porphyria cutanea tarda appear to be positive for cross reactive immunological material (CRIM).

Biochemical differentiation of the porphyrias.

OBJECTIVES: To differentiate the porphyrias by clinical and biochemical methods. DESIGN AND METHODS: We describe levels of blood, urine, and fecal porphyrins and their precursors in the porphyrias and present an algorithm for their biochemical differentiation. Diagnoses were established using clinical and biochemical data. Porphyrin analyses were performed by high performance liquid chromatography. RESULTS AND CONCLUSIONS: Plasma and urine porphyrin patterns were useful for diagnosis of porphyria cutanea tarda, but not the acute porphyrias. Erythropoietic protoporphyria was confirmed by erythrocyte protoporphyrin assay and erythrocyte fluorescence. Acute intermittent porphyria was diagnosed by increases in urine delta-aminolevulinic acid and porphobilinogen and confirmed by reduced erythrocyte porphobilinogen deaminase activity and normal or near-normal stool porphyrins. Variegate porphyria and hereditary coproporphyria were diagnosed by their characteristic stool porphyrin patterns. This appears to be the most convenient diagnostic approach until molecular abnormalities become more extensively defined and more widely available.

Hepatoerythropoietic porphyria.

In a case of hepatoerythropoietic porphyria (HEP) with unusual features, the patient had onset of photosensitivity in infancy, followed by spontaneous resolution of photosensitivity by the age of 7 years. Seven other cases of HEP have been found in the medical literature; the disease has systemic complications, mainly liver disease and anemia, and is inherited as an autosomal recessive trait. Certain clinical and biochemical features distinguish HEP from erythropoietic porphyria and erythropoietic protoporphyria, the two diseases with which HEP is often confused.