X-linked Dominant Protoporphyria Research Articles

PD13 Severe cutaneous manifestations in an Indian child with X-linked dominant erythropoietic protoporphyria

Abstract Erythropoietic protoporphyria (EPP) is usually caused by autosomal dominant mutations in FECH: raised protoporphyrin levels cause itching, burning and erythema after sun exposure, with facial scarring and sometimes liver damage. We report a child with the much rarer X-linked dominant form (XLDPP) and consider reasons for his unusually severe features. A 4-year-old boy living in India presented with long-standing erosions and scarring on the face and sides of the feet, and marked distal onycholysis with subungual hyperkeratosis affecting all nails, suggestive of pachyonychia congenita (PC). There was no relevant family history or parental consanguinity. He was anaemic (haemoglobin 7.2 g dL−1). Genetic testing revealed no variants in PC genes, but there was a hemizygous deletion in ALAS2, c.1706_1709del (p.Glu569GlyfsT er24) reported recurrently in XLDPP. Further review revealed a history of photosensitivity, low vitamin D3 and raised liver enzymes. Measurement of erythrocyte protoporphyrin was not available, but XLDPP was diagnosed on the basis of photosensitivity, liver abnormalities, probable photo-onycholysis and genetic testing. ALAS2 encodes 5-aminolaevulinate synthase, the first enzyme in the haem synthetic pathway. Most ALAS2 mutations block haemoglobin production resulting in sideroblastic anaemia. However, specific deletions, including this one, activate the pathway, increasing protoporphyrin to levels higher than what can be used in haematopoiesis. The manifestations of XLDPP therefore resemble EPP: protoporphyrin accumulation is caused in the former by increased production and in the latter by a block in its conversion to haem. Iron deficiency, common in Indian children, reduces haem production and consequently protoporphyrin utilization, potentially exacerbating the protoporphyrin accumulation caused by XLDPP. In a previous patient with XLDPP and anaemia due to gastrointestinal bleeding, iron therapy successfully lowered red cell protoporphyrin levels (Whatley SD, Ducamp S, Gouya L et al. C-terminal deletions in the ALAS2 gene lead to gain of function and cause X-linked dominant protoporphyria without anemia or iron overload. Am J Hum Genet 2008; 83:408–14). Nail dystrophy has not previously been reported in XLDPP. The appearance here is consistent with photo-onycholysis in a child whose feet are always exposed in sandals. The delay in diagnosing photosensitivity and severity of his skin changes can be attributed to the difficulty in interpreting symptoms in young children and to local conditions where sun exposure is unavoidable. Management here involves iron therapy, photoprotection, monitoring of liver function and genetic counselling; female carriers may also have symptoms. We are grateful to national experts for helpful discussion of this case.

X-linked dominant protoporphyria in a Chinese pedigree reveals a four-based deletion of ALAS2.

BackgroundX-linked dominant protoporphyria (XLDPP) is a rare, hereditary disorder that leads to hepatobiliary and hematologic abnormalities including increased erythrocyte protoporphyrin, cutaneous photosensitivity, and decreased iron stores that is caused by a pathogenic mutation of ALAS2 gene.MethodsThis study aimed to confirm the existence of XLDPP in a Chinese pedigree. We observed and described the dermatoscopic findings of this disorder under dermoscopy, and assessed photo damage in XLDPP patients using the Fotofinder system and very high frequency (VHF) skin ultrasonic system. We performed next generation sequencing and Sanger sequencing to detect and confirm genetic variants in DNA samples from the XLDPP family. Moreover, we monitored the hepatobiliary function as well as hematologic changes in related family members.ResultsAs compared to unaffected control subjects, patients exhibited evidence of severe cutaneous photodamage, causing photoaging, an increase in the size of the gallbladder, increased levels of protoporphyrin in red blood cells, an increase in blood levels of uroporphyrin and hematoporphyrin, and iron deficiency.ConclusionsXLDPP was validated by the identification of a four-base-pair deletion (c.1706_1709delAGTG, p.E569fs) in ALAS2 (NM_000032.4) in the proband which segregated with the disease in an X-linked dominant pattern, with hemizygous males being more severely affected than heterozygous females. We also found a missense variant in GATA Binding Protein 1 (GATA1).

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.

X-linked dominant protoporphyria: report of a pedigree and detection of ALAS2 gene mutations

Objective To report a pedigree with X-linked dominant protoporphyria (XLDPP), and to detect 5-aminolevulinic acid synthetase 2 (ALAS2) gene mutations in this pedigree. Methods A clinical investigation was performed in a pedigree with XLDPP, and relevant data were collected from family members. A next-generation sequencing method was applied to screen possible mutation sites, and Sanger sequencing was performed to determine pathogenic gene mutations. Dermoscopy was conducted to observe skin lesions in the patients with XLDPP, and the Fotofinder system and very high frequency (VHF) ultrasound system were utilized to assess the severity of photodamage. Liver and gallbladder ultrasonography as well as blood examination were performed for all the family members. Results A deletion mutation, c.1706-1709 ΔAGTG, was detected in the ALAS2 gene on the X chromosomes of all the patients in this family, which led to replacement or loss of 19-20 C-terminal residues through transcriptional frameshifting, and eventually caused an increase in ALAS2 activity. In the patients with XLDPP, skin photodamage was relatively severe; protoporphyrin-induced hepatobiliary damage was observed and aggravated with age; anemia and iron deficiency occurred sometimes. Conclusion The deletion mutation c.1706-1709 ΔAGTG of the ALAS2 gene may be the underlying cause of XLDPP in this pedigree. Key words: Porphyria, erythropoietic; Genetic diseases, X-linked; DNA mutational analysis; 5-Aminolevulinic acid synthetase 2 gene; Photoaging

Ambient Light Promotes Selective Subcellular Proteotoxicity after Endogenous and Exogenous Porphyrinogenic Stress

Hepatic accumulation of protoporphyrin-IX (PP-IX) in erythropoietic protoporphyria (EPP) or X-linked-dominant protoporphyria (XLP) cause liver damage. Hepatocyte nuclear lamin aggregation is a sensitive marker for PP-IX-mediated liver injury. We tested the hypothesis that extracellular or intracellular protoporphyria cause damage to different subcellular compartments, in a light-triggered manner. Three hepatoma cell lines (HepG2, Hepa-1, and Huh-7) were treated with exogenous PP-IX (mimicking XLP extrahepatic protoporphyria) or with the iron chelator deferoxamine and the porphyrin precursor 5-aminolevulinic acid (ALA) (mimicking intracellular protoporphyrin accumulation in EPP). Exogenous PP-IX accumulated predominantly in the nuclear fraction and caused nuclear shape deformation and cytoplasmic vacuoles containing electron-dense particles, whereas ALA+deferoxamine treatment resulted in higher PP-IX in the cytoplasmic fraction. Protein aggregation in the nuclear and cytoplasmic fractions paralleled PP-IX levels and, in cell culture, the effects were exclusively ambient light-mediated. PP-IX and ALA caused proteasomal inhibition, whereas endoplasmic reticulum protein aggregation was more prominent in ALA-treated cells. The enhanced ALA-related toxicity is likely due to generation of additional porphyrin intermediates including uroporphyrin and coproporphyrin, based on HPLC analysis of cell lysates and the culture medium, as well as cell-free experiments with uroporphyrin/coproporphyrin. Mouse livers from drug-induced porphyria phenocopied the in vitro findings, and mass spectrometry of liver proteins isolated in light/dark conditions showed diminished (as compared with light-harvested) but detectable aggregation under dark-harvested conditions. Therefore, PP-IX leads to endoplasmic reticulum stress and proteasome inhibition in a manner that depends on the source of porphyrin buildup and light exposure. Porphyrin-mediated selective protein aggregation provides a potential mechanism for porphyria-associated tissue injury.

Red cells from ferrochelatase-deficient erythropoietic protoporphyria patients are resistant to growth of malarial parasites

AbstractMany red cell polymorphisms are a result of selective pressure by the malarial parasite. Here, we add another red cell disease to the panoply of erythrocytic changes that give rise to resistance to malaria. Erythrocytes from individuals with erythropoietic protoporphyria (EPP) have low levels of the final enzyme in the heme biosynthetic pathway, ferrochelatase. Cells from these patients are resistant to the growth of Plasmodium falciparum malarial parasites. This phenomenon is due to the absence of ferrochelatase and not an accumulation of substrate, as demonstrated by the normal growth of P falciparum parasites in the EPP phenocopy, X-linked dominant protoporphyria, which has elevated substrate, and normal ferrochelatase levels. This observation was replicated in a mouse strain with a hypomorphic mutation in the murine ferrochelatase gene. The parasite enzyme is not essential for parasite growth as Plasmodium berghei parasites carrying a complete deletion of the ferrochelatase gene grow normally in erythrocytes, which confirms previous studies. That ferrochelatase is essential to parasite growth was confirmed by showing that inhibition of ferrochelatase using the specific competitive inhibitor, N-methylprotoporphyrin, produced a potent growth inhibition effect against cultures of P falciparum. This raises the possibility of targeting human ferrochelatase in a host-directed antimalarial strategy.

Erythropoietic Protoporphyric Red Blood Cells Are Resistant to the Growth of Malarial Parasites

Many red cell polymorphisms are a result of selective pressure by the malarial parasite. Here we add another red cell disease to the panoply of erythrocytic changes that give rise to resistance to malaria. Erythrocytes from individuals with erythropoietic protoporphyria (EPP) have low levels of the final enzyme in the heme biosynthetic pathway, ferrochelatase. Cells from these patients are resistant to the growth of the human malarial parasite, Plasmodium falciparum.We first compared the growth and replication rates of P. falciparum cultured in red cells from EPP patients (n=4) and normal erythrocytes. There was a two to three-fold reduction in parasite growth in the patient cells. Next we sought to exclude the possible negative effects on the parasite due to elevated porphyrins and reduced cell hemoglobin. To do this we employed the EPP phenocopy, X-linked dominant protoporphyria (XLDPP), which has normal ferrochelatase activity. Cells from three individuals with XLDPP supported completely normal rates of parasite growth, proving that the EPP resistance phenomenon was due to the absence of ferrochelatase.We also tested the requirement of host ferrochelatase during malarial infection by using mice with a hypomorphic mutation in the murine ferrochelatase gene and the rodent malarial species, P. chabaudi. Mice homozygous for the mutation, Fechm1Pas, have 5% residual ferrochelatase activity compared to wild-type littermates 1. Following infection, we observed an almost two fold reduction in peak parasitemia levels and two to three times greater rates of survival in the homozygous mice. Host ferrochelatase is therefore also necessary to sustain a normal malarial infection in mice.To determine the requirement of parasite-expressed ferrochelase, we produced a P. berghei parasite line carrying a complete deletion of the ferrochelatase gene. This strain grew normally in wild-type mouse erythrocytes, indicating that parasite ferrochelatase is dispensable during the erythrocytic stage of infection.A complete absence of ferrochelatase in humans (and mice) is not compatible with life, and therefore testing parasite growth in complete knockout cells was not possible. Instead, we used a specific competitive inhibitor of the enzyme, N-methylprotoporphyrin (NMPP) to eliminate all ferrochelatase activity from the parasite and red cell. Treatment of P. falciparum cultures with NMPP resulted in potent cytocidal and growth inhibition effects against both antimalarial drug-sensitive and drug-resistant parasite lines. The activity of NMPP could be competitively removed by titration of the ferrochelatase substrate, protoporphyrin IX, proving that the effects of NMPP were due to specific enzyme inhibition and not off-target effects. Therefore ferrochelatase activity is also essential for the Plasmodium parasite.We conclude that the refractoriness of ferrochelatse-deficient red cells to Plasmodium is due to the parasite’s reliance on the host enzyme. Host ferrochelatase is probably utilized by the parasite for the biosynthesis of heme. In support of this hypothesis, others have observed that red cell ferrochelatase is imported by intraerythrocytic Plasmodium and enzymatic is retained 2,3. Finally, based on this collective data, we propose human ferrochelatase is a valid and novel “host-directed” target for an antimalarial therapy. 1.Lyoumi S, Abitbol M, Andrieu V, et al. Increased plasma transferrin, altered body iron distribution, and microcytic hypochromic anemia in ferrochelatase-deficient mice. Blood. 2007;109(2):811-818.2.Bonday ZQ, Dhanasekaran S, Rangarajan PN, Padmanaban G. Import of host delta-aminolevulinate dehydratase into the malarial parasite: identification of a new drug target. Nat Med. 2000;6(8):898-903.3.Varadharajan S, Sagar BK, Rangarajan PN, Padmanaban G. Localization of ferrochelatase in Plasmodium falciparum. Biochem J. 2004;384(Pt 2):429-436. DisclosuresNo relevant conflicts of interest to declare.

Aminolevulinate synthase 2 mediates erythrocyte differentiation by regulating larval globin expression during Xenopus primary hematopoiesis

Hemoglobin synthesis by erythrocytes continues throughout a vertebrate’s lifetime. The mechanism of mammalian heme synthesis has been studied for many years; aminolevulinate synthase 2 (ALAS2), a heme synthetase, is associated with X-linked dominant protoporphyria in humans. Amphibian and mammalian blood cells differ, but little is known about amphibian embryonic hemoglobin synthesis. We investigated the function of the Xenopus alas2 gene (Xalas2) in primitive amphibian erythrocytes and found that it is first expressed in primitive erythroid cells before hemoglobin alpha 3 subunit (hba3) during primary hematopoiesis and in the posterior ventral blood islands at the tailbud stage. Xalas2 is not expressed during secondary hematopoiesis in the dorsal lateral plate. Hemoglobin was barely detectable by o-dianisidine staining and hba3 transcript levels decreased in Xalas2-knockdown embryos. These results suggest that Xalas2 might be able to synthesize hemoglobin during hematopoiesis and mediate erythrocyte differentiation by regulating hba3 expression in Xenopus laevis.

Heme-Related Blood Disorders

Heme biosynthesis in erythroid cells is intended primarily for the formation of hemoglobin. As in every cell, this synthesis requires a multi-step pathway that involves eight enzymes including the erythroid-specific δ-aminolevulinate synthase (ALAS2, the first regulated enzyme that converts glycine and succinyl CoA into ALA) and the ubiquitous ferrochelatase (FECH, the final enzyme). Heme biosynthesis also requires membrane transporters that are necessary to translocate glycine, precursors of heme, and heme itself between the mitochondria and the cytosol. Defects in normal porphyrin and/or heme synthesis and transport cause four major erythroid inherited disorders, which may or may not be associated with dyserythropoiesis (e.g., sideroblastic, microcytic anemia and/or hemolytic anemia): "X-linked" sideroblastic anemia (XLSA) and X-linked dominant protoporphyria (XLDPP) are two different and opposing disorders but related to altered gene encoding ALAS2 only. Defective activity of this enzyme due to mutations in the ALAS2 gene causes the XLSA phenotype, including microcytic, hypochromic anemia with abundant ringed sideroblasts in the bone marrow. Vice versa, gain-of-function mutations of ALAS2 are responsible of the XLDPP characterized by predominant accumulation of the hydrophobic protoporphyrin (PPIX, the last heme precursor) in the erythrocytes without anemia or sideroblasts. Furthermore, the glycine transporter (SLC25A38) and Glutaredoxin 5 genes are reported to be involved in human non-syndromic sideroblastic anemia. Congenital erythropoietic porphyria (CEP) is the rarest autosomal recessive disorder due to a deficiency in uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme biosynthetic pathway. CEP leads to excessive synthesis and accumulation of type I isomers of porphyrins in the reticulocytes, followed by intravascular hemolysis and severe anemia. The ALAS2 gene may act as a modifier gene in CEP patients (Figueras J et al, Blood. 2011;118(6):1443-51). Erythropoietic protoporphyria (EPP) results from a partial deficiency of FECH and leads similarly to XLDPP, to deleterious accumulation of PPIX in erythroid cells. Most EPP patients present intrans to a FECH gene mutation an IVS3-48C hypomorphic allele due to a splice mutation. Abnormal spliced mRNA is degraded which contributes to the lowest FECH enzyme activity and allowed EPP phenotype expression. We have identified an antisense oligonucleotide (ASO) to redirect splicing from cryptic to physiological site and showed that the ASO-based therapy mediates normal splice rescue of FECH mRNA and reduction by 60 percent of PPIX overproduction in primary cultures of EPP erythroid progenitors. Therapeutic approaches to target both ALAS2 inhibition and heme-level reduction may be useful in other erythroid disorders such as thalassemia (where reduced heme biosynthesis was shown to improve the clinical phenotype) or the Diamond-Blackfan anemia (DBA). Indeed, in some DBA patients, an unusual mRNA splicing of heme exporter FLVCR has been found, reminiscent of Flvcr1-deficient mice that develop a DBA-like phenotype with erythroid heme accumulation. Thus, FLVCR may act as a modifier gene for DBA phenotypic variability. Recent advances in understanding the pathogenesis and molecular genetic heterogeneity of heme-related disorders have led to improved diagnosis and treatment. These advances include DNA-based diagnoses for all the porphyrias and some porphyrins and heme transporters, new understanding of the pathogenesis of the erythropoietic disorders, and new and experimental treatments such as chronic erythrocyte transfusions, bone marrow or hematopoietic stem cell transplants, and experimental pharmacologic chaperone and stem cell gene therapies for erythropoietic porphyrias. Disclosures:No relevant conflicts of interest to declare.

Photosensitivity in the Elderly: Think of Protoporphyria

Erythropoietic protoporphyria (EPP) is an uncommon photosensitivity usually produced by an inactivating germline mutation affecting ferrochelatase, the last enzyme in the heme biosynthetic pathway. Free protoporphyrin accumulates in erythrocytes, causing burning and stinging sensations a few minutes after sun exposure. The disease usually becomes apparent in childhood. Many features of EPP are present in X-linked dominant protoporphyria (XLDPP), a disease caused by a gain-of-function mutation in the gene that encodes 5-aminolevulinate …

Photosensitivity in the Elderly—Think of Late-Onset Protoporphyria

Photosensitivity is the clinical hallmark of both erythropoietic protoporphyria (EPP) and X-linked dominant protoporphyria (XLDPP). Both disorders result from a hereditary dysfunction in heme biosynthesis. Disease onset is usually in early childhood. However, rare patients with late-onset EPP in association with a myeloproliferative disorder or myelodysplastic syndrome have been reported. In this issue, Livideanu et al. describe the first patient with late-onset XLDPP.

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.

Molecular and functional analysis of the C-terminal region of human erythroid-specific 5-aminolevulinic synthase associated with X-linked dominant protoporphyria (XLDPP)

Frameshift mutations in the last coding exon of the 5-aminolevulinate synthase (ALAS) 2 gene were described to activate the enzyme causing increased levels of zinc- and metal-free protoporphyrin in patients with X-linked dominant protoporphyria (XLDPP). Only two such so-called gain-of-function mutations have been reported since the description of XLDPP in 2008. In this study of four newly identified XLDPP families, we identified two novel ALAS2 gene mutations, a nonsense p.Q548X and a frameshift c.1651-1677del26bp, along with a known mutation (delAGTG) found in two unrelated families. Of relevance, a de novo somatic and germinal mosaicism was present in a delAGTG family. Such a phenomenon may explain the high proportion of this mutation in XLDPP worldwide. Enhancements of over 3- and 14-fold in the catalytic rate and specificity constant of purified recombinant XLDPP variants in relation to those of wild-type ALAS2 confirmed the gain of function ascribed to these enzymes. The fact that both p.Q548X and c.1651-1677del26bp are located in close proximity and upstream from the two previously described mutations led us to propose the presence of a large gain-of-function domain within the C-terminus of ALAS2. To test this hypothesis, we generated four additional nonsense mutants (p.A539X, p.G544X, p.G576X and p.V583X) surrounding the human XLDPP mutations and defined an ALAS2 gain-of-function domain with a minimal size of 33 amino acids. The identification of this gain-of-function domain provides important information on the enzymatic activity of ALAS2, which was proposed to be constitutively inhibited, either directly or indirectly, through its own C-terminus.

ALAS2 acts as a modifier gene in patients with congenital erythropoietic porphyria

AbstractMutations in the uroporphyrinogen III synthase (UROS) gene cause congenital erythropoietic porphyria (CEP), an autosomal-recessive inborn error of erythroid heme biosynthesis. Clinical features of CEP include dermatologic and hematologic abnormalities of variable severity. The discovery of a new type of erythroid porphyria, X-linked dominant protoporphyria (XLDPP), which results from increased activity of 5-aminolevulinate synthase 2 (ALAS2), the rate-controlling enzyme of erythroid heme synthesis, led us to hypothesize that the CEP phenotype may be modulated by sequence variations in the ALAS2 gene. We genotyped ALAS2 in 4 unrelated CEP patients exhibiting the same C73R/P248Q UROS genotype. The most severe of the CEP patients, a young girl, proved to be heterozygous for a novel ALAS2 mutation: c.1757 A > T in exon 11. This mutation is predicted to affect the highly conserved and penultimate C-terminal amino acid of ALAS2 (Y586). The rate of 5-aminolevulinate release from Y586F was significantly increased over that of wild-type ALAS2. The contribution of the ALAS2 gain-of-function mutation to the CEP phenotype underscores the importance of modifier genes underlying CEP. We propose that ALAS2 gene mutations should be considered not only as causative of X-linked sideroblastic anemia (XLSA) and XLDPP but may also modulate gene function in other erythropoietic disorders.

Results of a pilot external quality assessment study on free protoporphyrin in erythrocytes

Quantification of erythrocyte protoporphyrins (ePP) is essential to establish the diagnosis of erythropoietic protoporphyria, a form of chronic porphyria that is not very rare (prevalence roughly 1:50,000), and clinically characterized by painful phototoxic skin reactions that usually start in early childhood (1, 2), and X-linked dominant protoporphyria, a recently (2008) described metabolic disorder with similar clinical features (3). While PP with zinc chelated as the central ion (zinc PP) is increased in iron deficiency anemia and inefficient erythropoesis, substantial increases ()50-fold) in metal-free ePP is pathognomonic for protoporphyria. Erythrocyte protoporphyrins are measured using various methods, and standardisation of analytic procedures has not been addressed at present. In order to assess the comparability of free ePP results obtained in clinical samples using different analytical methods, we performed an inter-laboratory comparison study (4). In this trial, lyophilized aliquots of three samples (A–C) were shipped to the participating laboratories. The samples were based on washed red blood cells which were lysed by repeated freeze-thaw-cycles prior to dispensing and lyophilization. Sample B was obtained from an adult male patient suffering from protoporphyria; sample C was from a healthy volunteer; and sample A was a 1q1 mix of samples B and C. Six laboratories from Europe, North-America and Asia-performing ePP quantification routinely, contributed results,

Delayed diagnosis and diminished quality of life in erythropoietic protoporphyria: results of a cross-sectional study in Sweden

Delayed diagnosis and diminished quality of life in erythropoietic protoporphyria: results of a cross-sectional study in Sweden

Afamelanotide, an agonistic analog of α-melanocyte-stimulating hormone, in dermal phototoxicity of erythropoietic protoporphyria

Importance of the field: Afamelanotide, an α-melanocyte stimulating hormone (MSH) agonistic analog is a first-in-class therapeutic. Its application to protoporphyria (PP), a disease associated with absolute sunlight-intolerance is discussed.Areas covered in this review: The genetics and existing therapy of the inherited disease PP comprising both erythropoietic protoporphyria and X-linked dominant protoporphyria. The physiological and pharmacological actions of α-MSH and afamelanotide including receptor-mediated intracellular signaling and effects of receptor polymorphisms. Adverse effects and safety issues.What the reader will gain: The clinical severity and the necessity for an effective therapy for the rare disease PP are illustrated by a short, up-to-date portrait. A condensed description of clinically important aspects of α-MSH signaling, physiological, pharmacological and safety issues of afamelanotide applied to humans and the rational for its potential efficacy in PP are given. The different trials of afamelanotide in PP and their most recent results are discussed.Take home message: Although early, results of the first trials of afamelanotide for PP are promising and the risk–safety profile appears favorable today. We expect afamelanotide and analogs thereof to be a prospective therapeutic tool in light-related skin diseases, and in future this drug class might prove effectiveness in other medical conditions.

La protoporphyrie érythropoïétique : une maladie, deux gènes et trois mécanismes moléculaires

Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis that results from an accumulation of protoporphyrin IX in erythroid cells, plasma, skin and liver. EPP leads to acute photosensitivity and, in about 2% of patients, liver disease. EPP is a complex syndrome in which two genes are independently involved: FECH and ALAS2. More than 96% of unrelated EPP patients have ferrochelatase (FECH) deficiency (MIM 177000). Four percent of them present with autosomal recessive inheritance with two mutated FECH alleles. In dominant cases (95%) the inheritance of a common hypomorphic IVS3-48C FECH allele trans to a deleterious FECH mutation reduces FECH activity below a critical threshold. The frequency of the IVS3-48C allele differs widely from the Japanese (45%), to Black West Africans (< 1%) populations. These differences in the frequency of this single common SNP account for the prevalence of overt EPP in different countries and for the absence of EPP in Black Africans. The phylogenic origin of the IVS3-48C haplotypes strongly suggests that the IVS3-48C allele arose from a single recent mutational event that occurred 60 Kyears ago. Acquired somatic mutation of FECH secondary to myeloid disease may also exceptionally cause EPP (< 1%). Finally, about 4% of unrelated EPP patients have X-linked dominant protoporphyria (XLDPP) (MIM 300752) caused by gain-of-function mutations in the ALAS2 gene leading to an increased erythroid heme biosynthesis and subsequently an accumulation of protoporphyrin without any FECH deficiency.

Molecular epidemiology of erythropoietic protoporphyria in the U.K.

Erythropoietic protoporphyria (EPP) is a cutaneous porphyria caused by mutations in the ferrochelatase (FECH) or, less frequently, the delta-aminolaevulinate synthase 2 (ALAS2) gene. Predictive genetic counselling requires accurate molecular diagnosis and knowledge of patterns of inheritance. To investigate the molecular epidemiology of EPP in the U.K. DNA samples from 191 unrelated patients resident in the U.K. were analysed for mutations in the FECH and ALAS2 genes and for the FECH IVS3-48 dimorphism. Mutations were identified in 179 (94%) patients. Most (169; 94%) had a FECH mutation on one allele and were classified as having pseudodominant EPP (psdEPP); seven (4%) patients had FECH mutations on both alleles (autosomal recessive EPP) and three (2%) patients had ALAS2 mutations (X-linked dominant protoporphyria). The FECH IVS3-48C allele was strongly associated with psdEPP and with the absence of mutations at the FECH or ALAS2 loci. Fifty-six FECH mutations were identified, 19 being previously unreported. Missense mutations were predominant in autosomal recessive EPP (82%) but not in psdEPP (32%). One mutation (c.314 + 2T>G) was present in 41 (24%) of EPP families, most of whom appeared to be descended from a common ancestor resident in the north of England. These data define the prevalence and molecular epidemiology of each type of EPP in the U.K.

Erythropoietic protoporphyria

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.