Diagnosis and treatment of the acute porphyrias: an interdisciplinary challenge

The acute hepatic porphyrias: current status and future challenges

The porphyrias are predominantly inherited metabolic disorders, which result from a specific deficiency of one of the eight enzymes along the pathway of haem biosynthesis. Historically, they have been classified into hepatic and erythropoietic forms, based on the primary site of expression of the prevailing dysfunctional enzyme. From a clinical point of view, however, it is more convenient to subdivide them into acute and non-acute porphyrias, thereby primarily considering the potential occurrence of life-threatening acute neurovisceral attacks. Unrecognised or untreated, such an acute porphyric attack is associated with a significant mortality of up to 10%. The acute hepatic porphyrias comprise acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and δ-aminolevulinic acid dehydratase deficiency porphyria. Making a precise diagnosis may be difficult because the different types of porphyrias may show overlapping clinical and biochemical characteristics. To date, the therapeutic possibilities are limited and mainly symptomatic. In this overview we report on what is currently known about pathogenesis, clinic, diagnostics, and therapy of the acute hepatic porphyrias. We further point out actual and future challenges in the management of these diseases.

Genetic and biochemical studies in Argentinean patients with variegate porphyria

BACKGROUND

A partial deficiency in Protoporphyrinogen oxidase (PPOX) produces the mixed disorder Variegate Porphyria (VP), the second acute porphyria more frequent in Argentina. Identification of patients with an overt VP is absolutely important because treatment depends on an accurate diagnosis but more critical is the identification of asymptomatic relatives to avoid acute attacks which may progress to death.

METHODS

We have studied at molecular level 18 new Argentinean patients biochemically diagnosed as VP. PPOX gene was amplified in one or in twelve PCR reactions. All coding exons, flanking intronic and promoter regions were manual or automatically sequenced. For RT-PCR studies RNA was retrotranscripted, amplified and sequenced. PPOX activity in those families carrying a new and uncharacterized mutation was performed.

RESULTS

All affected individuals harboured mutations in heterozygous state. Nine novel mutations and 3 already reported mutations were identified. Six of the novel mutations were single nucleotide substitutions, 2 were small deletions and one a small insertion. Three single nucleotide substitutions and the insertion were at exon-intron boundaries. Two of the single nucleotide substitutions, c.471G>A and c.807G>A and the insertion (c.388+3insT) were close to the splice donor sites in exons 5, 7 and intron 4 respectively. The other single nucleotide substitution was a transversion in the last base of intron 7, g.3912G>C (c.808-1G>C) so altering the consensus acceptor splice site. However, only in the first case the abnormal band showing the skipping of exon 5 was detected. The other single nucleotide substitutions were transversions: c.101A>T, c.995G>C and c.670 T>G that result in p.E34V, p.G332A and W224G aminoacid substitutions in exons 3, 10 and 7 respectively. Activity measurements indicate that these mutations reduced about 50% PPOX activity and also that they co-segregate with this reduced activity value. Two frameshift mutations, c.133delT and c.925delA, were detected in exons 3 and 9 respectively. The first leads to an early termination signal 22 codons downstream (p.S45fsX67) and the second leads to a stop codon 5 codons downstream (p.I309fsX314). One reported mutation was a missense mutation (p.G232R) and 2 were frameshift mutations: c.1082insC and 1043insT. The last mutation was detected in six new apparently unrelated Argentinean families.

CONCLUSION

Molecular analysis in available family members revealed 14 individuals who were silent carriers of VP. Molecular techniques represent the most accurate approach to identify unaffected carriers and to provide accurate genetic counselling for asymptomatic individuals. The initial screening includes the insertion search.

[Laboratory tests and therapeutic strategies for the porphyrias]

The porphyrias are a heterogeneous group of predominantly hereditary metabolic diseases resulting from a dysfunction of heme biosynthesis. Most of the porphyrias can manifest with a broad range of cutaneous symptoms on the sun-exposed areas of the body, whereas other variants reveal life-threatening acute neurological attacks. Further, mixed types of porphyrias exist. Besides the skin, other organs can be affected, such as the liver and the central nervous system. Therefore, interdisciplinary supervision of these patients is mandatory. In this review we will first present the clinical picture and diagnosis of the porphyrias, including the specific biochemical laboratory tests and a diagnostic algorithm. Thereafter, the current therapeutic concepts will be briefly addressed. Finally, we introduce the European Porphyria Initiative (EPI), an association of various European porphyria centers that is aiming at gathering the broad experience of internationally renowned porphyria experts for the development of European consensus guidelines for diagnosis and treatment of these metabolic disorders.

Hereditäre Photodermatosen

Hereditary photodermatoses are characterized by an increased photosensitivity caused by an inherited single gene defect. With few exceptions, they manifest in early childhood, reveal heterogeneous clinical symptoms, and are difficult to treat. Although these diseases are rare, it is very important to make an accurate diagnosis on the basis of clinical symptoms, specific diagnostic tests, and direct DNA analysis. We review the spectrum of inherited photodermatoses, including porphyria cutanea tarda, erythropoietic protoporphyria, actinic prurigo, Kindler syndrome, and disorders associated with a defect in DNA repair, including xeroderma pigmentosum, trichothiodystrophy, Cockayne syndrome, and Bloom syndrome. Early diagnosis may prevent complications associated with prolonged unprotected exposure to sunlight and makes it possible to offer genetic counseling and, when indicated, prenatal diagnosis to families at risk for these rare heritable disorders.

Dual porphyrias revisited

The porphyrias are clinically and genetically heterogeneous metabolic diseases, which predominantly result from a hereditary dysfunction in the pathway of haeme biosynthesis. Currently, at least eight different forms of porphyrias can be differentiated, all of them characterized by a specific enzyme deficiency that is either inherited in an autosomal-dominant fashion, autosomal recessively or, in the case of porphyria cutanea tarda, might also be acquired. All genes encoding these enzymes have been cloned and several mutations underlying the different types of porphyrias have been reported. Traditionally, the diagnosis of porphyria is made on the basis of clinical symptoms, characteristic biochemical findings and enzyme assays. In some porphyria patients and families, however, these diagnostic tools can reveal simultaneous findings compatible with two different forms of porphyria, a phenomenon referred to as dual porphyria. Here, we give an overview on what is currently known about these peculiar variants of porphyria and suggest that, whenever feasible, molecular genetic analysis should complement the analytical techniques used to characterize patients and families in which a double enzymatic deficiency within the haeme biosynthetic pathway is assumed.

Kortikale Amaurosis und Status epilepticus bei akuter Porphyrie

The most common neurologic manifestations of acute intermittent porphyria (AIP) are autonomic visceral neuropathy, peripheral motor neuropathy, and CNS dysfunctions including seizures and neuropsychiatric disturbances. In rare instances, however, AIP patients have presented with acute cortical blindness. We present a 20-year-old woman who suffered her first attack of AIP. Following 1 week of abdominal pain, she was transferred from a surgical department because of sudden visual loss and deterioration of consciousness. On admission, she developed several generalized seizures. Magnetic resonance imaging showed bilateral DWI lesions occipitally and in the left anterior circulation. Cerebrospinal fluid, MR angiography, and duplex ultrasound were normal. On the following day, sedation and intubation became necessary because of a generalized status epilepticus. Analysis of porphyrinogens in blood, urine and stool showed significantly elevated values. Intravenous therapy with häm-arginate was initiated and antiepileptic therapy was changed to gagabentine. Under this therapeutical regime she remained stable and extubation was possible 48 h later.

ED presentation of acute porphyria

Abdominal pain is a common complaint for visits to ED. Among the causes of abdominal pain, the acute porphyria may confuse emergency physicians. With wide range of unspecific symptoms and signs, acute porphyria is rarely considered as a differential diagnosis of acute abdomen in ED. Some patients even receive unnecessary surgery. There are 32 patients who visited the ED of National Taiwan University Hospital because of acute porphyric attacks over the past 13 years. Ten patients (3 males and 7 females) were diagnosed with acute porphyria for the first time at ED. The onset of age ranged from 17 to 55 years (mean, 32 years). All of our patients presented with abdominal pain but without fever, dermatologic, and neurologic symptoms that are typically presented in acute porphyria. On the average, most of them repeatedly sought for medical help because of persistent symptoms for 4 times before being definitely diagnosed and thus receiving the optimal treatment. Meanwhile, all patients needed at least 2 kinds of analgesic, and most of them needed narcotic analgesia for pain control before diagnosis. The most commonest point of tenderness is over epigastrium (7 of 10 patients). The laboratory and image studies of our patients were of no diagnostic value for acute porphyria, except for Watson-Schwartz test. In summary, our study revealed that when a patient after puberty with repetitive visits because of severe abdominal pain without reasonable causes and needs narcotics for pain control, acute porphyria should be taken into consideration.

Diagnosis and treatment of the hepatic porphyrias

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.