Prenatal diagnosis in congenital erythropoietic porphyria by metabolic measurement and DNA mutation analysis

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

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

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.

Mutational analysis of uroporphyrinogen III cosynthase gene in Iranian families with congenital erythropoietic porphyria

Porphyrias are rare metabolic hereditary diseases originating from defects in specific enzymes involved in the heme biosynthesis pathway. Congenital erythropoietic porphyria (CEP) is the rarest autosomal recessive porphyria resulting from a deficiency of uroporphyrinogen III cosynthase (UROS), the fourth enzyme in heme biosynthesis. CEP leads to an excessive production and accumulation of type Ι porphyrins in bone marrow, skin and several other tissues. Clinical manifestations are presented in childhood with severe cutaneous photosensitivity, blistering, scarring and deformation of the hands and the loss of eyebrows and eyelashes. Less than 200 cases of CEP have been reported to date. Four CEP patients and their family members were studied for the first time in Iran. A missense mutation in the UROS gene was identified in this family. A, T to C change at nucleotide 34313, leading to a substitution of Leucine by Proline at codon 237, was observed in the homozygous state in these 4 patients and heterozygous state in their parents. Our data from the Iranian population emphasizes the importance of codon 237 alone, given the rarity of this disease. This fact can be taken into consideration in the mutational analysis of UROS. This work emphasizes the advantages of molecular genetic techniques as diagnostic tools for the detection of clinically asymptomatic heterozygous mutation carriers as well as CEP within families.

Congenital erythropoietic porphyria: characterization of murine models of the severe common (C73R/C73R) and later-onset genotypes

Congenital erythropoietic porphyria (CEP) is an autosomal recessive disorder due to the deficient activity of uroporphyrinogen III synthase (UROS). Knock-in mouse models were generated for the common, hematologically severe human genotype, C73R/C73R, and milder genotypes (C73R/V99L and V99L/V99L). The specific activities of the UROS enzyme in the livers and erythrocytes of these mice averaged approximately 1.2%, 11% and 19% of normal, respectively. C73R/C73R mice that survived fetal life to weaning age (~12%) had a severe microcytic hypochromic anemia (hemoglobin 7.9 g/dL, mean cellular volume 26.6 fL, mean cellular hemoglobin content 27.4 g/dL, red cell distribution width 37.7%, reticulocytes 19%) and massively accumulated isomer I porphyrins (95, 183 and 44 μmol/L in erythrocytes, spleen and liver, respectively), but a nearly normal lifespan. In adult C73R/C73R mice, spleen and liver weights were 8.2- and 1.5-fold increased, respectively. C73R/V99L mice were mildly anemic (hemoglobin was 14.0 g/dL and mean cellular hemoglobin was 13.3), with minimally accumulated porphyrins (0.10, 5.54 and 0.58 μmol/L in erythrocytes, spleen and liver, respectively), whereas adult V99L/V99L mice were normal. Of note, even the mildest genotype, V99L/V99L, exhibited porphyria in utero, which disappeared by 2 months of age. These severe and mild mouse models inform therapeutic interventions and permit further investigation of the porphyrin-induced hematopathology, which leads to photo-induced cutaneous lesions. Of significance for therapeutic intervention, these mouse models suggest that only 11% of wild-type activity might be needed to reverse the pathology in CEP patients.

Diagnosis and management of the erythropoietic porphyrias

The erythropoietic porphyrias are erythropoietic protoporphyria, and congenital erythropietic porphyria. Diagnosis is made based on clinical manifestations, and their characteristic porphyrin profiles. There are multiple treatment options for these two porphyrias, however, aside from bone marrow transplant for CEP, none is curative.

Congenital erythropoietic porphyria (Günther's disease): two cases with very early prenatal manifestation and cystic hygroma

Congenital erythropoietic porphyria (CEP) or Günther's disease is the rarest form of the porphyrias. The disease is usually diagnosed at birth or during early infancy, but rarely in utero. We describe here the first two cases of very early prenatal expression of CEP with cystic hygroma diagnosed at 14 weeks in the first fetus and at 19 weeks in the second. Both fetuses presented with severe nonimmune hydrops fetalis as early as 19 and 22 weeks, associated with intrauterine growth retardation, hyperechogenic kidneys and bones. Amniotic fluid was dark brown and uro- and coproporphyrin I was dramatically increased. Molecular screening of the CEP gene detected heterozygous C73R mutation in both fetuses, the other parental mutation being as yet unknown.

Congenital erythropoietic porphyria: prenatal diagnosis and autopsy findings in two sibling fetuses

Congenital erythropoietic porphyria is an autosomal recessive disease characterized by a deficiency of uroporphyrinogen III cosynthetase activity, with diffuse tissue accumulation of specific type I porphyrins. The diagnosis of this disease was made in two fetuses, who were siblings, and from a Caucasian nonconsanguinous family. The first fetus died in utero with hydrops fetalis and anemia, but without an etiopathogenic diagnosis. In the second case, the diagnosis was based on pink fluorescence of the amniotic fluid examined fortuitously in sunlight. DNA analysis showed that the fetus was heteroallelic for the mutation C73R. The autopsy showed brown skin, and at histological examination, porphyrin pigment was deposited in many tissues. Retrospectively, similar deposits were found in the tissues of the first fetus.

The cutaneous porphyrias

Deficiencies of 7 enzymes in the heme biosynthetic pathway result in the development of porphyrias. Two of the porphyrias, aminolevulinate dehydratase deficiency porphyria and acute intermittent porphyria do not have cutaneous findings. Cutaneous findings in the other porphyrias could be subdivided into acute phototoxicity and subacute phototoxicity. In addition, 2 of the porphyrias, hereditary coproporphyria and variegate porphyria have both cutaneous and neurovisceral findings. Now that chromosomal assignments for all the genes of the defective enzymes have been mode, prenatal diagnosis is possible for congenital erythropoietic porphyria, and in vitro gene therapy has been successfully performed for congenital erythropoietic porphyria and erythropoietic protoporphyria.

A rare cause of fetal ascites: A case report of Günther's disease

Despite an arsenal of ever-improving diagnostic tools, determining the precise etiology of fetal ascites is not always possible. We report a case history where moderately-severe fetal ascites was retrospectively determined to be due to Günther's disease (congenital erythropoietic porphyria). The infant was found to carry the mutation associated with the most severe disease phenotype in which fetal hydrops has been described.

The cutaneous porphyrias: a review. The British Photodermatology Group

Many patients with cutaneous porphyria have curable or controllable disease; untreated porphyria may prove fatal. The genetic defects and mechanisms underlying porphyria are steadily being delineated, treatments have become more appropriate and genetic counselling is now more accurate. A summary of the basic diagnostic features, management and recent advances in the cutaneous porphyrias is presented, based on a workshop held by the British Photodermatology Group.

Congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is one of the rarest autosomal-recessive disorders of the porphyrin metabolism caused by the homozygous defect of uroporphyrinogen III cosynthase. High amounts of uroporphyrin I accumulate in all cells and tissues, reflected by an increased erythrocyte porphyrin concentration and excretion of high porphyrin amounts in urine and feces. Dermal deposits of uroporphyrin frequently induce a dramatic phototoxic oxygen-dependent skin damage with extensive ulcerations and mutilations. Splenomegaly and hemolytic anemia are typical internal symptoms. Skeletal changes such as osteolysis and calcifications are frequent. Up to date 130 cases of CEP have been published. Splenectomy and erythrocyte transfusions showed some beneficial effect. Bone marrow transplantation was performed in 3 patients and stem cell transplantation in 1. The best therapy is the avoidance of sunlight. We give a report on our latest cases of CEP.

The genetic bases of the porphyrias

The porphyrias are disorders that result from the inherited or acquired dysregulation of one of the eight enzymes in the porphyrin-heme biosynthetic pathway. The different types of porphyrias often show overlapping findings with regard to clinical and/or biochemical features. Therefore, the establishment of screening methods for the identification of underlying mutations on the basis of direct DNA analysis may provide a more reliable approach for diagnosis of the different types of porphyrias. Here, we provide an overview of molecular biological screening techniques for mutations and the molecular bases of the porphyrias.

Update on enzyme and molecular defects in porphyria

Each porphyria results from decreased activity of one of the enzymes of haem biosynthesis. The molecular basis of enzyme deficiencies in acute intermittent porphyria (AIP), variegate porphyria (VP) and congenital erythropoietic porphyria (CEP) is outlined. All three conditions show extensive allelic heterogeneity. In the autosomal dominant disorders, AIP and VP, no genotype/phenotype correlations have been demonstrated, and the explanation for their low clinical penetrance remains uncertain. In AIP and VP, mutational analysis is superior to biochemical methods for screening families for latent porphyria. In the autosomal recessive condition, CEP, there is some genotype/phenotype correlation--one common mutation (C73R) being associated with severe disease in homozygotes. Porphyria cutanea tarda (PCT) is not a simple monogenic disorder. Patients appear to have an inherited susceptibility to inactivation of hepatic uroporphyrinogen decarboxylase (UROD) as part of a response to hepatocyte injury by alcohol, HCV and other agents. Inherited factors that, in combination, may predispose to PCT include mutations in the UROD gene, present in about 20% of patients, and the C282Y mutation in the haemochromatosis (HFE) gene.

Novel point mutation in the uroporphyrinogen III synthase gene causes congenital erythropoietic porphyria of a Japanese family

The molecular basis of the uroporphyrinogen III synthase (UROIIIS) deficiency was investigated in a member of a Japanese family. This defect in heme biosynthesis is responsible for a rare autosomal recessive disease: congenital erythropoietic porphyria (CEP) or Günther's disease. The patient was homozygous for a novel missense mutation: a G to T transition of nucleotide 7 that predicted a valine to phenylalanine substitution at residue 3 (V3F). The parents were heterozygous for the same mutation. The loss of UROIIIS activity was verified by an in vitro assay system. The corresponding mutated protein was expressed in Escherichia coli and no residual activity was observed. Further studies are needed to determine whether the mutations of the UROIIIS gene (UROS) have a specific profile in Japan compared to European or American countries.