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Loss-of-function ferrochelatase and gain-of-function erythroid-specific 5-aminolevulinate synthase mutations causing erythropoietic protoporphyria and x-linked protoporphyria in North American patients reveal novel mutations and a high prevalence of X-linked protoporphyria.

ABSTRACT: Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are inborn errors of heme biosynthesis with the same phenotype but resulting from autosomal recessive loss-of-function mutations in the ferrochelatase (FECH) gene and gain-of-function mutations in the X-linked erythroid-specific 5-aminolevulinate synthase (ALAS2) gene, respectively. The EPP phenotype is characterized by acute, painful, cutaneous photosensitivity and elevated erythrocyte protoporphyrin levels. We report the FECH and ALAS2 mutations in 155 unrelated North American patients with the EPP phenotype. FECH sequencing and dosage analyses identified 140 patients with EPP: 134 with one loss-of-function allele and the common IVS3-48T>C low expression allele, three with two loss-of-function mutations and three with one loss-of-function mutation and two low expression alleles. There were 48 previously reported and 23 novel FECH mutations. The remaining 15 probands had ALAS2 gain-of-function mutations causing XLP: 13 with the previously reported deletion, c.1706_1709delAGTG, and two with novel mutations, c.1734delG and c.1642C>T(p.Q548X). Notably, XLP represented ~10% of EPP phenotype patients in North America, two to five times more than in Western Europe. XLP males had twofold higher erythrocyte protoporphyrin levels than EPP patients, predisposing to more severe photosensitivity and liver disease. Identification of XLP patients permits accurate diagnosis and counseling of at-risk relatives and asymptomatic heterozygotes.

SUBMITTER: Balwani M

PROVIDER: S-EPMC3646094 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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Loss-of-function ferrochelatase and gain-of-function erythroid-specific 5-aminolevulinate synthase mutations causing erythropoietic protoporphyria and x-linked protoporphyria in North American patients reveal novel mutations and a high prevalence of X-linked protoporphyria.

Balwani Manisha M Doheny Dana D Bishop David F DF Nazarenko Irina I Yasuda Makiko M Dailey Harry A HA Anderson Karl E KE Bissell D Montgomery DM Bloomer Joseph J Bonkovsky Herbert L HL Phillips John D JD Liu Lawrence L Desnick Robert J RJ

Molecular medicine (Cambridge, Mass.) 20130430

Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are inborn errors of heme biosynthesis with the same phenotype but resulting from autosomal recessive loss-of-function mutations in the ferrochelatase (FECH) gene and gain-of-function mutations in the X-linked erythroid-specific 5-aminolevulinate synthase (ALAS2) gene, respectively. The EPP phenotype is characterized by acute, painful, cutaneous photosensitivity and elevated erythrocyte protoporphyrin levels. We report the FEC ...[more]

PMID: 23364466

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Project description:Erythropoietic protoporphyria (EPP) is an inherited disorder of the haem metabolic pathway characterised by accumulation of protoporphyrin in blood, erythrocytes and tissues, and cutaneous manifestations of photosensitivity. EPP has been reported worldwide, with prevalence between 1:75,000 and 1:200,000. It usually manifests in early infancy upon the first sun exposures. EPP is characterised by cutaneous manifestations of acute painful photosensitivity with erythema and oedema, sometimes with petechiae, together with stinging and burning sensations upon exposure to sunlight, without blisters. These episodes have a variable severity depending on the exposure duration and may result in chronic permanent lesions on exposed skin. As protoporphyrin is a lipophilic molecule that is excreted by the liver, EPP patients are at risk of cholelithiasis with obstructive episodes, and chronic liver disease that might evolve to rapid acute liver failure. In most patients, EPP results from a partial deficiency of the last enzyme of the haem biosynthetic pathway, ferrochelatase, EC 4.99.1.1/FECH (encoded by the FECH gene). EPP appears to be inherited as an autosomal dominant disease, the clinical expression of which is modulated by the presence of the hypomorphic FECH IVS3-48C allele trans, but recessive inheritance with two mutated FECH alleles has also been described. In about 2% of patients, overt disease was recently shown to be caused by gain-of-function mutations in the erythroid-specific aminolevulinic acid synthase 2 (ALAS2/ALAS, EC 2.3.1.27) gene and named X-linked dominant protoporphyria. Diagnosis is established by finding increased levels of protoporphyrin in plasma and red blood cells, and detection of a plasma fluorescence peak at 634 nm. Investigations for hepatic involvement, ferrochelatase activity level, genetic analysis (FECH mutations, presence of the hypomorphic FECH IVS3-48C allele trans and ALAS2 mutations) and family studies are advisable. Differential diagnosis includes phototoxic drug reactions, hydroa vacciniforme, solar urticaria, contact dermatitis, angio-oedema and, in some cases, other types of porphyria. Management includes avoidance of exposure to light, reduction of protoporphyrin levels and prevention of progression of possible liver disease to liver failure. As the major risk in EPP patients is liver disease, a regular follow-up of hepatic involvement is essential. Sequential hepatic and bone marrow transplantation should be considered as a suitable treatment for most severe cases of EPP with hepatic involvement. EPP is a lifelong disorder whose prognosis depends on the evolution of the hepatic disease. However, photosensitivity may have a significant impact on quality of life of EPP patients.

Project description:Importance:Autosomal recessive erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are rare photodermatoses presenting with variable degrees of painful phototoxicity that markedly affects quality of life. The clinical variability, determinants of severity, and genotype/phenotype correlations of these diseases are not well characterized. Objective:To describe the baseline clinical characteristics, genotypes, and determinants of disease severity in a large patient cohort with EPP or XLP. Design, Setting, and Participants:A prospective observational study was conducted among patients with confirmed diagnoses of EPP or XLP from November 1, 2010, to December 6, 2015, at 6 academic medical centers of the Porphyrias Consortium of the National Institutes of Health Rare Diseases Clinical Research Network. Detailed medical histories, including history of phototoxicity and treatment, were collected on standardized case report forms. Patients underwent baseline laboratory testing, total erythrocyte protoporphyrin (ePPIX) testing, and molecular genetic testing. Data were entered into a centralized database. Main Outcomes and Measures:Results of biochemical and genetic tests were explored for association with clinical phenotype in patients with EPP or XLP. Results:Of the 226 patients in the study (113 female and 113 male patients; mean [SD] age, 36.7 [17.0] years), 186 (82.3%) had EPP with a FECH (OMIM 612386) mutation and the common low-expression FECH allele IVS3-48T>C, and only 1 patient had 2 FECH mutations. Twenty-two patients had XLP (9.7%; 10 male and 12 female patients), and 9 patients (4.0%) had elevated ePPIX levels and symptoms consistent with protoporphyria but no detectable mutation in the FECH or ALAS2 (OMIM 301300) gene. Samples of DNA could not be obtained from 8 patients. Patients' mean (SD) age at symptom onset was 4.4 (4.4) years. Anemia (107 [47.3%]), history of liver dysfunction (62 [27.4%]), and gallstones (53 [23.5%]) were commonly reported. Higher ePPIX levels were associated with earlier age of symptom onset (median ePPIX levels for those who developed symptoms before vs after 1 year of age, 1744 vs 1567 µg/dL; P?=?.02), less sun tolerance (median ePPIX levels for those reporting symptoms before vs after 10 minutes of sun exposure, 2233 vs 1524 µg/dL; P???.001), and increased risk of liver dysfunction (median ePPIX levels for those with liver dysfunction vs normal liver function, 2016 vs 1510 µg/dL; P?=?.003). Patients with EPP and FECH missense mutations had significantly lower ePPIX levels than those with other mutations (1462 vs 1702 µg/dL; P?=?.01). Male patients with XLP had significantly higher ePPIX levels, on average, than did patients with EPP (3574 vs 1669 µg/dL; P?<?.001). Marked clinical variability was seen in female patients with XLP owing to random X-chromosomal inactivation. Conclusions and Relevance:These data suggest that higher ePPIX levels are a major determinant of disease severity and risk of liver dysfunction in patients with EPP or XLP. These findings provide a framework for clinical monitoring and management of these disorders.

Dataset Information

Loss-of-function ferrochelatase and gain-of-function erythroid-specific 5-aminolevulinate synthase mutations causing erythropoietic protoporphyria and x-linked protoporphyria in North American patients reveal novel mutations and a high prevalence of X-linked protoporphyria.

Publications

Loss-of-function ferrochelatase and gain-of-function erythroid-specific 5-aminolevulinate synthase mutations causing erythropoietic protoporphyria and x-linked protoporphyria in North American patients reveal novel mutations and a high prevalence of X-linked protoporphyria.

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