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To-Figueras J, Erwin AL, Aguilera P, Millet O, Desnick RJ. Congenital erythropoietic porphyria. Liver Int 2024; 44:1842-1855. [PMID: 38717058 DOI: 10.1111/liv.15958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2024] [Revised: 04/16/2024] [Accepted: 04/18/2024] [Indexed: 07/17/2024]
Abstract
Congenital erythropoietic porphyria (CEP) is a rare autosomal recessive disease due to the deficient, but not absent, activity of uroporphyrinogen III synthase (UROS), the fourth enzyme in the heme biosynthesis pathway. Biallelic variants in the UROS gene result in decreased UROS enzymatic activity and the accumulation of non-physiologic Type I porphyrins in cells and fluids. Overproduced uroporphyrins in haematopoietic cells are released into the circulation and distributed to tissues, inducing primarily hematologic and dermatologic symptoms. The clinical manifestations vary in severity ranging from non-immune hydrops fetalis in utero to mild dermatologic manifestations in adults. Here, the biochemical, molecular and clinical features of CEP as well as current and new treatment options, including the rescue of UROS enzyme activity by chaperones, are presented.
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Affiliation(s)
- Jordi To-Figueras
- Biochemistry and Molecular Genetics Unit, Hospital Clinic, University of Barcelona, Barcelona, Spain
| | - Angelika L Erwin
- Center for Personalized Genetic Healthcare, Cleveland Clinic Community Care, Cleveland Clinic, Cleveland, Ohio, USA
| | - Paula Aguilera
- Dermatology Unit, Hospital Clinic, University of Barcelona, Barcelona, Spain
| | - Oscar Millet
- Precision Medicine and Metabolism Laboratory, CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bilbao, Spain
| | - Robert J Desnick
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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2
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Chen KL, Kuemmet TJ, Chiu YE. Progressive blistering and hypertrichosis in a young child. Pediatr Dermatol 2019; 36:951-952. [PMID: 31778569 DOI: 10.1111/pde.13977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Kristen L Chen
- Department of Dermatology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Travis J Kuemmet
- Department of Dermatology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Yvonne E Chiu
- Departments of Dermatology (Pediatric Dermatology) and Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin
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3
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Urquiza P, Laín A, Sanz-Parra A, Moreno J, Bernardo-Seisdedos G, Dubus P, González E, Gutiérrez-de-Juan V, García S, Eraña H, San Juan I, Macías I, Ben Bdira F, Pluta P, Ortega G, Oyarzábal J, González-Muñiz R, Rodríguez-Cuesta J, Anguita J, Díez E, Blouin JM, de Verneuil H, Mato JM, Richard E, Falcón-Pérez JM, Castilla J, Millet O. Repurposing ciclopirox as a pharmacological chaperone in a model of congenital erythropoietic porphyria. Sci Transl Med 2019; 10:10/459/eaat7467. [PMID: 30232228 DOI: 10.1126/scitranslmed.aat7467] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2018] [Revised: 06/04/2018] [Accepted: 08/23/2018] [Indexed: 12/30/2022]
Abstract
Congenital erythropoietic porphyria is a rare autosomal recessive disease produced by deficient activity of uroporphyrinogen III synthase, the fourth enzyme in the heme biosynthetic pathway. The disease affects many organs, can be life-threatening, and currently lacks curative treatments. Inherited mutations most commonly reduce the enzyme's stability, altering its homeostasis and ultimately blunting intracellular heme production. This results in uroporphyrin by-product accumulation in the body, aggravating associated pathological symptoms such as skin photosensitivity and disfiguring phototoxic cutaneous lesions. We demonstrated that the synthetic marketed antifungal ciclopirox binds to the enzyme, stabilizing it. Ciclopirox targeted the enzyme at an allosteric site distant from the active center and did not affect the enzyme's catalytic role. The drug restored enzymatic activity in vitro and ex vivo and was able to alleviate most clinical symptoms of congenital erythropoietic porphyria in a genetic mouse model of the disease at subtoxic concentrations. Our findings establish a possible line of therapeutic intervention against congenital erythropoietic porphyria, which is potentially applicable to most of deleterious missense mutations causing this devastating disease.
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Affiliation(s)
- Pedro Urquiza
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Ana Laín
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Arantza Sanz-Parra
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Jorge Moreno
- Prion Research Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | | | - Pierre Dubus
- Univerité de Bordeaux, Bordeaux Research in Translational Oncology, INSERM U1053, F-33000 Bordeaux, France.,INSERM, Biothérapie des Maladies Génétiques, Inflammatoires et Cancers, U1035, Bordeaux, France
| | | | | | | | - Hasier Eraña
- Atlas Molecular Pharma S. L., 48160 Derio, Spain
| | - Itxaso San Juan
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Iratxe Macías
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Fredj Ben Bdira
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain.,Department of Macromolecular Biochemistry, Leiden Institute of Chemistry, 2300 RA Leiden, Netherlands
| | - Paula Pluta
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Gabriel Ortega
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain.,Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106-9510, USA
| | - Julen Oyarzábal
- Small Molecule Discovery Platform, Center for Applied Medical Research, University of Navarra, 31008 Pamplona, Spain
| | | | | | - Juan Anguita
- Animal Facility, CIC bioGUNE, 48160 Derio, Spain.,Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain.,Macrophage and Tick Vaccine Laboratory, CIC bioGUNE, 48160 Derio, Spain
| | - Emilio Díez
- Atlas Molecular Pharma S. L., 48160 Derio, Spain
| | - Jean-Marc Blouin
- Université de Bordeaux, Biothérapie des Maladies Génétiques, Inflammatoires et Cancers, U1035, F-33000 Bordeaux, France
| | - Hubert de Verneuil
- Université de Bordeaux, Biothérapie des Maladies Génétiques, Inflammatoires et Cancers, U1035, F-33000 Bordeaux, France
| | - José M Mato
- Liver Metabolism Laboratory, CIC bioGUNE, 48160 Derio, Spain.,CIBERehd-ISCiii, 28029 Madrid, Spain
| | - Emmanuel Richard
- Université de Bordeaux, Biothérapie des Maladies Génétiques, Inflammatoires et Cancers, U1035, F-33000 Bordeaux, France
| | - Juan M Falcón-Pérez
- Exosomes Laboratory, CIC bioGUNE, 48160 Derio, Spain.,Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain.,CIBERehd-ISCiii, 28029 Madrid, Spain
| | - Joaquín Castilla
- Prion Research Laboratory, CIC bioGUNE, 48160 Derio, Spain.,Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
| | - Oscar Millet
- Protein Stability and Inherited Disease Laboratory, CIC bioGUNE, 48160 Derio, Spain.
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4
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Luo E, Liu H, Zhao Q, Shi B, Chen Q. Dental-craniofacial manifestation and treatment of rare diseases. Int J Oral Sci 2019; 11:9. [PMID: 30783081 PMCID: PMC6381182 DOI: 10.1038/s41368-018-0041-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 10/22/2018] [Accepted: 10/28/2018] [Indexed: 02/05/2023] Open
Abstract
Rare diseases are usually genetic, chronic and incurable disorders with a relatively low incidence. Developments in the diagnosis and management of rare diseases have been relatively slow due to a lack of sufficient profit motivation and market to attract research by companies. However, due to the attention of government and society as well as economic development, rare diseases have been gradually become an increasing concern. As several dental-craniofacial manifestations are associated with rare diseases, we summarize them in this study to help dentists and oral maxillofacial surgeons provide an early diagnosis and subsequent management for patients with these rare diseases.
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Affiliation(s)
- En Luo
- State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Hanghang Liu
- State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Qiucheng Zhao
- State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Bing Shi
- State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
| | - Qianming Chen
- State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
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5
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Di Pierro E, Brancaleoni V, Granata F. Advances in understanding the pathogenesis of congenital erythropoietic porphyria. Br J Haematol 2016; 173:365-79. [PMID: 26969896 DOI: 10.1111/bjh.13978] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Congenital erythropoietic porphyria (CEP) is a rare genetic disease resulting from the remarkable deficient activity of uroporphyrinogen III synthase, the fourth enzyme of the haem biosynthetic pathway. This enzyme defect results in overproduction of the non-physiological and pathogenic porphyrin isomers, uroporphyrin I and coproporphyrin I. The predominant clinical characteristics of CEP include bullous cutaneous photosensitivity to visible light from early infancy, progressive photomutilation and chronic haemolytic anaemia. The severity of clinical manifestations is markedly heterogeneous among patients; and interdependence between disease severity and porphyrin amount in the tissues has been pointed out. A more pronounced endogenous production of porphyrins concomitant to activation of ALAS2, the first and rate-limiting of the haem synthesis enzymes in erythroid cells, has also been reported. CEP is inherited as autosomal recessive or X-linked trait due to mutations in UROS or GATA1 genes; however an involvement of other causative or modifier genes cannot be ruled out.
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Affiliation(s)
- Elena Di Pierro
- U.O. di Medicina Interna, Fondazione IRCCS Cà Granda - Ospedale Maggiore Policlinico, Milano, Italy
| | - Valentina Brancaleoni
- U.O. di Medicina Interna, Fondazione IRCCS Cà Granda - Ospedale Maggiore Policlinico, Milano, Italy
| | - Francesca Granata
- U.O. di Medicina Interna, Fondazione IRCCS Cà Granda - Ospedale Maggiore Policlinico, Milano, Italy
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Nicolas JM, Chanteux H, Mancel V, Dubin GM, Gerin B, Staelens L, Depelchin O, Kervyn S. N-alkylprotoporphyrin formation and hepatic porphyria in dogs after administration of a new antiepileptic drug candidate: mechanism and species specificity. Toxicol Sci 2014; 141:353-64. [PMID: 24973095 DOI: 10.1093/toxsci/kfu131] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A new antiepileptic synaptic vesicle 2a (SV2a) ligand drug candidate was tested in 4-week oral toxicity studies in rat and dog. Brown pigment inclusions were found in the liver of high-dose dogs. The morphology of the deposits and the accompanying liver changes (increased plasma liver enzymes, increased total hepatic porphyrin level, decreased liver ferrochelatase activity, combined induction, and inactivation of cytochrome P-450 CYP2B11) suggested disruption of the heme biosynthetic cascade. None of these changes was seen in rat although this species was exposed to higher parent drug levels. Toxicokinetic analysis and in vitro metabolism assays in hepatocytes showed that dog is more prone to oxidize the drug candidate than rat. Mass spectrometry analysis of liver samples from treated dogs revealed an N-alkylprotoporphyrin adduct. The elucidation of its chemical structure suggested that the drug transforms into a reactive metabolite which is structurally related to a known reference porphyrogenic agent allylisopropylacetamide. That particular metabolite, primarily produced in dog but neither in rat nor in human, has the potential to alkylate the prosthetic heme of CYP. Overall, the data suggested that the drug candidate should not be porphyrogenic in human. This case study further exemplifies the species variability in the susceptibility to drug-induced porphyria.
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Affiliation(s)
- Jean-Marie Nicolas
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | - Hugues Chanteux
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | - Valérie Mancel
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | | | - Brigitte Gerin
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | - Ludovicus Staelens
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | - Olympe Depelchin
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
| | - Sophie Kervyn
- UCB Pharma S.A., Non-Clinical Development, B-1420 Braine l'Alleud, Belgium
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7
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Standerwick RG, Yen EH, Pliska B. Orthodontic treatment considerations for a patient with erythropoietic protoporphyria. Am J Orthod Dentofacial Orthop 2013; 144:899-908. [DOI: 10.1016/j.ajodo.2013.02.032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2013] [Revised: 02/01/2013] [Accepted: 02/01/2013] [Indexed: 10/26/2022]
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8
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Clinical manifestations and diagnostic challenges in acute porphyrias. Case Rep Hematol 2013; 2013:628602. [PMID: 23476835 PMCID: PMC3583083 DOI: 10.1155/2013/628602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 01/08/2013] [Indexed: 12/21/2022] Open
Abstract
The porphyrias are a group of disorders characterized by an enzyme deficiency in the heme biosynthetic pathway. These can be classified into either erythropoietic or hepatic forms depending on the site of the major enzyme deficiency. The diagnosis of acute porphyrias, however, can be very challenging due to overlapping features amongst the various types. Initial suspicion is based on a myriad of clinical manifestations, which then are confirmed by laboratory testing where available. Genetic testing is now also available for the different types of porphyrias, aiding in the definitive diagnosis. Here, we present a challenging case of porphyria in a patient with end-stage renal disease and present the diagnostic challenges associated with the case and the ways forward.
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9
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Peroxidase-like activity of uncoupled cytochrome P450: studies with bilirubin and toxicological implications of uncoupling. Biochem Pharmacol 2012; 84:374-82. [PMID: 22564776 DOI: 10.1016/j.bcp.2012.04.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 04/17/2012] [Accepted: 04/19/2012] [Indexed: 01/04/2023]
Abstract
The NADPH-dependent consumption of O(2) by cytochrome P450 BM3 was stimulated by either laurate or perfluorolaurate, but the NADPH/O(2) molar consumption ratios were approximately 1 and 2, respectively, indicating that perfluorolaurate does not become oxygenated by BM3 and oxygen undergoes full reduction to water. The nature of this catalytic cycle uncoupled to hydroxylation was explored using bilirubin as a molecular probe. During uncoupling with perfluorolaurate bilirubin was degraded and stimulated O(2) uptake by an approximately equimolar amount. No stimulation of oxygen uptake was caused by bilirubin in presence of NADPH alone or in presence of laurate together with NADPH; under these conditions little degradation of bilirubin was observed. Mesobilirubin was also degraded during uncoupling with perfluorolaurate, whereas biliverdin (which lacks the central methene bridge present in rubins) was unaffected. It is suggested that the CYP ferryl oxygen species abstracts a hydrogen atom from the central methene bridge of bilirubin to generate a radical, which is further dehydrogenated to biliverdin or else binds O(2) and undergoes fragmentation. We conclude that the uncoupled catalytic cycle of cytochrome P450 has properties resembling those of a peroxidase and that bilirubin is rapidly oxidized as a peroxidase substrate. The potential toxicological significance of cytochrome P450 uncoupling is considered.
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10
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Erupciones inflamatorias y purpúricas. DERMATOLOGÍA NEONATAL 2009. [PMCID: PMC7161408 DOI: 10.1016/b978-84-8086-390-2.50019-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
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11
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Baselga E, Torrelo A. Inflammatory and Purpuric Eruptions. NEONATAL DERMATOLOGY 2008. [PMCID: PMC7315339 DOI: 10.1016/b978-1-4160-3432-2.50022-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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12
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Nezamzadeh R, Seubert A, Pohlenz J, Brenig B. Identification of a mutation in the ovine uroporphyrinogen decarboxylase (UROD) gene associated with a type of porphyria. Anim Genet 2005; 36:297-302. [PMID: 16026339 DOI: 10.1111/j.1365-2052.2005.01301.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Porphyria is a group of at least eight diseases caused by abnormalities in the chemical steps that lead to haeme production. The different types of porphyria show different signs and symptoms and can be strongly influenced by environmental factors. Mutations of the uroporphyrinogen decarboxylase (UROD) gene have been shown to be causative for porphyria cutanea tarda (PCT) in humans. Porphyria is a rare disorder in livestock. Although disorders of haeme biosynthesis have been described in cattle, pigs, sheep and cats, PCT has only been reported in pigs. We observed typical signs of porphyria (photosensitivity and porphyrinuria) in a flock of German Blackface sheep and postulated that the porphyria could be caused by a mutation in the UROD gene. To investigate this, we cloned and sequenced the ovine UROD gene. We identified a single point mutation (C --> T) in UROD which leads to an amino acid substitution at Leu 131 Pro, which is located within the active cleft site of the UROD protein.
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Affiliation(s)
- R Nezamzadeh
- Institute of Veterinary Medicine, University of Göttingen,Göttingen, Germany
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13
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de Villiers JNP, Kotze MJ, van Heerden CJ, Sadie A, Gardner HFJ, Liebenberg J, van Zyl R, du Plessis L, Kimberg M, Frank J, Warnich L. Overrepresentation of the founder PPOX gene mutation R59W in a South African patient with severe clinical manifestation of porphyria. Exp Dermatol 2005; 14:50-5. [PMID: 15660919 DOI: 10.1111/j.0906-6705.2005.00228.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A patient, who presented with abdominal pain and severe photosensitivity that resulted in scarring and mutilation of the fingers, nose and ears, was referred for biochemical assessment of porphyria and DNA screening. Although these clinical manifestations were suggestive of both acute porphyria and congenital erythropoietic porphyria, the biochemical profile was consistent with variegate porphyria (VP). Analysis of the protoporphyrinogen oxidase (PPOX) gene underlying VP resulted in the identification of the founder mutation R59W in a heterozygous state in this patient. Despite extensive mutation analysis, no other potential disease-causing genetic alterations could be detected in the PPOX gene or the uroporphyrinogen III synthase gene. Slight overrepresentation of the mutant PPOX allele was however, observed repeatedly in DNA of the proband compared to other R59W heterozygotes, including his mother who also tested positive for mutation R59W using restriction enzyme analysis and direct DNA sequencing. Confirmation of this phenomenon by real-time polymerase chain reaction analysis and microsatellite analysis, using highly informative markers flanking the PPOX gene, raised the possibility of partial homozygosity for VP in this patient. This study represents the first report of overrepresentation of mutation R59W in a patient with a severe form of VP. A homozygote for the R59W mutation has never been detected, and the severe clinical manifestation observed in our patient is consistent with the hypothesis that such a genotype will not be compatible with life.
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Affiliation(s)
- J Nico P de Villiers
- Division of Human Genetics, Faculty of Health Sciences, University of Stellenbosch, Tygerberg, South Africa
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14
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Abstract
Porphyrias are a peculiar group of diseases resulting from hereditary or acquired partial deficiencies in seven of the eight enzymes in the biosynthetic pathway of heme. Biosynthesis of heme takes place in the erythropoietic system or in the hepatic tissue. Depending on the main location of the enzyme defect, porphyrias can be classified as erythropoietic or hepatic. There are seven basic clinical forms of porphyria related to a deficiency of each of the involved enzymes. Clinical manifestations in porphyria may be neurovisceral or cutaneous. Patients may present with acute attacks (acute porphyrias), cutaneous lesions (cutaneous porphyrias), or both (mixed porphyrias). Study of patients supected of having porphyria should include several steps: 1) clinical evaluation, 2) biochemical study, which enables us to classify the patient to a specific form of porphyria, followed if possible by 3) enzymatic assay(s), and 4) genetic studies to confirm an enzyme deficiency and its level and the causal genetic mutation. Unfortunately no curative treatment is available for any of the porphyrias. However, symptomatic treatments are available and are discussed in this article.
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Affiliation(s)
- M Lecha
- Department of Dermatology, Hospital Clinic, University of Barcelona, Barcelona, Spain.
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15
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Abstract
The biosynthesis of porphyrins is one of the most conserved parthways known, about the same sequence of reactions taking place in all species. By associating different metals, porphyrins give rise to the "pigments of life": chlorophyll, haem and cobalamin. The unique tetrapyrrolic structure enables it to function in an array of reactions as a single electron carrier and as a catalyst for redox reactions. In this capacity, it constitutes the prosthetic group of enzymes participating in cellular respiration, in conversion reactions involving steroids and lipophilic xenobiotics, in protective mechanisms directed against oxidative stress and in pathways providing central messenger molecules. The formation of haem is accomplished by a sequence of eight dedicated enzymes encoded by different genes, some being active in ubiquitous as well as in erythroid isoforms. Large differences between the participating enzymes with regard to catalytic power, with low capacity steps positioned early in the catalytic chain, constitute a bar against substrate overloading of enzymes processing porphyrins, thus preventing accumulation in the body of these phototoxic compounds under physiological conditions. Most of the haem in the body is produced by the liver and bone marrow, but the mechanisms applied for the control of the synthesis differ between the two organs. The extremely potent hemeprotein enzymes formed in the liver are rapidly turned over in response to current metabolic needs. They have half-lives in the order of minutes or hours and are restored by fast-acting mechanisms for the de novo synthesis, when needed. Uninterrupted and instant availability of the compound is secured by acute deinhibition of the initial enzyme of the synthetic chain, ubiquitous 5-aminolevulinate synthase (ALAS-1), in response to drain of the free cellular haem pool caused by prevailing demands for hemeproteins or by increased catabolism of the compound. In contrast, in the erythroid progenitor cell the haem synthetic machinery is designed for uninterrupted production of huge amounts of haem for combination with globin chains to form hemoglobin at a steady rate. In the erythron the synthesis of the enzymes participating in the formation of haem is under control of erythropoietin, formed under hypoxic conditions. In the absence of iron, to be incorporated in the porphyrin formed in the last step of the synthesis, the mRNA of erythroid 5-aminolevulinate synthase (ALAS-2) is blocked by attachment of an iron-responsive element (IRE) binding cytosolic protein, and transcription of this key enzyme is inhibited. In humans, the genes for each of the haem synthetic enzymes may become the target of mutations that give rise to impaired cellular enzyme activity. Seven of the enzyme deficiencies are associated with accumulation of toxic intermediaries and with disease entities termed porphyrias. The acute porphyrias are characterized by attacks of neuropsychiatric symptoms, which may be due to a toxic surplus of the porphyrin presursor 5-aminolevulinic acid, or a consequence of a deficit of vital hemeproteins resulting from impaired synthesis of haem. In the cutaneous porphyrias, impairment of enzymatic steps where porphyrins are processed gives rise to solar hypersensitivity due to accumulation of phototoxic porphyrins in the skin. Early diagnosis, information to the patient regarding the nature of the illness and counselling aimed at avoidance of triggering factors are cornerstones in the handling of the porphyric diseases. Gene analysis is of incomparable diagnostic reliability in carrier detection, but biochemical methods must be applied in the important task of monitoring porphyric disease activity. In most forms of porphyria the gene carriers run the risk of development of associated diseases in liver or kidneys, a circumstance that prompts application of well-structured surveillance programs.
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Affiliation(s)
- S Thunell
- Porphyria Centre Sweden, CMMS, Huddinge University Hospital, Sweden.
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16
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Abstract
Porphyrias are divided into erythropoietic and hepatic manifestations. Erythropoietic porphyrias are characterized by cutaneous symptoms and appear in early childhood. Erythropoietic protoporphyria is complicated by cholestatic liver cirrhosis and progressive hepatic failure in 10%, of patients. Acute hepatic porphyrias (delta-aminolaevulinic acid dehydratase deficiency porphyria, acute intermittent porphyria, hereditary coproporphyria and variegate porphyria) are characterized by variable extrahepatic gastrointestinal, neurological-psychiatric and cardiovascular manifestations requiring early diagnosis to avoid life-threatening complications. Acute hepatic porphyrias are pharmacogenetic and molecular regulatory diseases (without porphyrin accumulation) mainly induced by drugs, sex hormones, fasting or alcohol. The disease process depends on the derepression of hepatic delta-aminolaevulinic acid synthase following haem depletion. In contrast to the acute porphyrias, nonacute, chronic hepatic porphyrias such as porphyria cutanea tarda are porphyrin accumulation disorders leading to cutaneous symptoms associated with liver disease, especially caused by alcohol or viral hepatitis. Alcohol, oestrogens, haemodialysis, hepatitis C and AIDS are triggering factors. Porphyria cutanea tarda is the most common porphyria, followed by acute intermittent porphyria and erythropoietic protoporphyria. The molecular genetics of the porphyrias is very heterogenous. Nearly every family has its own mutation. The mutations identified account for the corresponding enzymatic deficiencies, which may remain clinically silent throughout life. Thus, the recognition of the overt disorder with extrahepatic manifestations depends on the demonstration of biochemical abnormalities due to these primary defects and compensatory hepatic overexpression of hepatic delta-aminolaevulinic acid synthase in the acute porphyrias. Consequently, haem precursors are synthesized in excess. The increased metabolites upstream of the enzymatic defect are excreted into urine and faeces. The diagnosis is based on their evaluation. Primary enzymatic or molecular analyses are noncontributary and may be misleading. Acute polysymptomatic exacerbations accompany a high excretory constellation of porphyrin precursors delta-aminolaevulinic acid and porphobilinogen. Homozygous or compound heterozygous variants of acute hepatic porphyrias may already manifest in childhood.
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MESH Headings
- Animals
- Humans
- Porphyria Cutanea Tarda/diagnosis
- Porphyria Cutanea Tarda/genetics
- Porphyria Cutanea Tarda/physiopathology
- Porphyria Cutanea Tarda/therapy
- Porphyria, Acute Intermittent/diagnosis
- Porphyria, Acute Intermittent/genetics
- Porphyria, Acute Intermittent/physiopathology
- Porphyria, Acute Intermittent/therapy
- Porphyria, Erythropoietic/diagnosis
- Porphyria, Erythropoietic/genetics
- Porphyria, Erythropoietic/physiopathology
- Porphyria, Erythropoietic/therapy
- Porphyrias, Hepatic/diagnosis
- Porphyrias, Hepatic/genetics
- Porphyrias, Hepatic/physiopathology
- Porphyrias, Hepatic/therapy
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Affiliation(s)
- U Gross
- Division of Clinical Biochemistry, Faculty of Medicine, Philipps University, Marburg, Germany.
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