Richard J. Hift

C-Terminal Deletions in the ALAS2 Gene Lead to Gain of Function and Cause X-linked Dominant Protoporphyria without Anemia or Iron Overload

All reported mutations in ALAS2, which encodes the rate-regulating enzyme of erythroid heme biosynthesis, cause X-linked sideroblastic anemia. We describe eight families with ALAS2 deletions, either c.1706-1709 delAGTG (p.E569GfsX24) or c.1699-1700 delAT (p.M567EfsX2), resulting in frameshifts that lead to replacement or deletion of the 19-20 C-terminal residues of the enzyme. Prokaryotic expression studies show that both mutations markedly increase ALAS2 activity. These gain-of-function mutations cause a previously unrecognized form of porphyria, X-linked dominant protoporphyria, characterized biochemically by a high proportion of zinc-protoporphyrin in erythrocytes, in which a mismatch between protoporphyrin production and the heme requirement of differentiating erythroid cells leads to overproduction of protoporphyrin in amounts sufficient to cause photosensitivity and liver disease.

The acute porphyrias

Public attention has been drawn to the acute porphyrias in the past few years by speculation that they affected the character of George III and the creative genius of Vincent van Gogh. During the same period, there have been important advances in the understanding of the molecular basis of the acute porphyrias and in diagnosis and the clinical management of patients and their families. Four types of porphyria are classified as acute because they produce acute neurovisceral crises (panel). Here, we outline current knowledge of the three autosomal dominant types: acute intermittent porphyria, variegate porphyria, and hereditary coproporphyria.

An analysis of 112 acute porphyric attacks in Cape Town, South Africa: Evidence that acute intermittent porphyria and variegate porphyria differ in susceptibility and severity.

Abstract: Four forms of porphyria may present clinically with the acute attack, an episodic, severe, and potentially life-threatening manifestation characterized by abdominal and neurologic symptoms. We describe our experience with 112 consecutive attacks observed and treated in 25 patients with the 2 most common forms of acute porphyria in Cape Town, South Africa; 25 attacks in 10 patients with variegate porphyria and 87 attacks in 14 patients with acute intermittent porphyria. The remaining patient experienced more than 100 sequential, severe, and poorly remitting attacks, which are not included in our analysis. In our population, the relative risk of an acute attack in acute intermittent porphyria compared with that in variegate porphyria was 14.3 (confidence intervals, 6.3-32.7). Patients with variegate porphyria were significantly older (median age at first attack, 30 yr) than those with acute intermittent porphyria (median age at first attack, 23.5 yr; p < 0.0001), and demonstrated an equal sex ratio, whereas the male:female ratio in acute intermittent porphyria was 2:12 (p < 0.0001). There was a significant difference in the incidence of factors precipitating the acute attack. Drug exposure was a frequent precipitant of the acute attack in variegate porphyria, whereas hormonal factors were more important in acute intermittent porphyria (p < 0.00001). Patients with acute intermittent porphyria also showed a trend to earlier and more frequent recurrent acute attacks following the initial admission. Mean urine precursor levels, blood pressure, pulse rate, and heme arginate requirement were all significantly higher in patients with acute intermittent porphyria. No significant difference in the frequency of serious complications or in outcome could be shown. We describe our experience with treatment with heme arginate, and provide evidence that heme arginate results in a prompt and statistically significant improvement in symptoms. The incidence of serious complications and mortality in this series was low, confirming a trend to an increasingly good prognosis for patients with acute porphyria who receive expert treatment. Abbreviations: AIP = acute intermittent porphyria, ALA = aminolevulinic acid, CT = computed tomography, PBG = porphobilinogen, VP = variegate porphyria.

Liver disease in erythropoietic protoporphyria: insights and implications for management

The porphyrias are a group of disorders caused by defects in haem biosynthesis (fig 1). Of the seven main types of porphyria recognised, two are characterised by associated liver disease (table 1). In porphyria cutanea tarda it is the liver disease which leads to the onset of the porphyria, characterised by blistering, hirsutes and skin fragility of sun-exposed skin. A number of different liver diseases may precipitate porphyria cutanea tarda including haemochromatosis, alcoholic liver disease and hepatitis C. In contrast, in erythropoietic protoporphyria (EPP) it is the porphyria itself which leads to liver disease, due to progressive deposition and accumulation of insoluble protoporphyrin IX in hepatocytes and bile canaliculi. View this table: Table 1  Liver disease and the porphyrias: names and patterns of inheritance for the seven main clinical variants of porphyria, highlighting those characterised by concomitant liver disease Figure 1  The haem biosynthetic pathway showing the enzyme deficiency associated with porphyria cutanea tarda (PCT) and erythropoietic protoporphyria (EPP). The final step in this pathway involves the incorporation of iron into the middle of the ring structure of protoporphyrin IX to form haem. EPP is an inborn error of haem biosynthesis caused by mutations in the gene encoding the mitochondrial enzyme ferrochelatase (FECH), the final enzyme in the haem biosynthetic pathway (fig 1).1–5 It was first described by Magnus et al in 1962.6 Ferrochelatase catalyses the insertion of ferrous iron into protoporphyrin to form haem, and when defective or deficient, accumulation of protoporphyrin ensues. Ferrochelatase is active in cells that produce haem including erythroid precursors in the bone marrow7 and hepatocytes.8 However, the majority of protoporphyrin (80% or more) originates from bone marrow with most of the remainder generated by the liver (fig 2).7,9 Figure 2  The fate of protoporphyrin IX in erythropoietic protoporphyria. Protoporphyrin accumulates in the maturing red blood cells …

A systematic study of the clinical and biochemical expression of variegate porphyria in a large South African family.

Background  Variegate porphyria (VP) is an autosomal dominant disorder associated with deficient haem synthesis. Recent reports indicate that the clinical penetrance of VP may have been overestimated in studies which predated the availability of DNA‐based testing for VP.

Molecular characterization of erythropoietic protoporphyria in South Africa

Background  Erythropoietic protoporphyria (EPP) results from a partial deficiency of ferrochelatase (FECH). Clinical expression normally requires coinheritance of a common hypomorphic FECH allele (IVS3‐48C) in trans to a deleterious (primary) FECH mutation.

A review of the clinical presentation, natural history and inheritance of variegate porphyria: its implausibility as the source of the ‘Royal Malady’

It has been suggested that King George III of Great Britain suffered from the haem biosynthetic disorder, variegate porphyria. This diagnosis is pervasive throughout the scientific and popular literature, and is often referred to as the ‘Royal Malady.’ The authors believe it inappropriate to view the case for porphyria purely in terms of symptoms, as has generally been the case in his presumptive acute porphyria diagnosis. Accordingly, this review provides a current description of the natural history and clinical presentation of the porphyrias, against which we measure the case for porphyria in George III and his relatives. The authors have critically assessed the prevalence of porphyria in a population, the expected patterns and frequency of inheritance, its penetrance and its expected natural history in affected individuals, and conclude that neither George nor his relatives had porphyria, based on four principal reasons. First, the rarity of the disease mandates a very low prior probability, and therefore implies a vanishingly low positive predictive value for any diagnostic indicator of low specificity, such as a historical reading of the symptoms. Second, penetrance of this autosomal dominant disorder is approximately 40%, and one may expect to have identified characteristic clinical features of porphyria in a large number of descendants without difficulty. Third, the symptoms of both George III and his relatives are highly atypical for porphyria and are more appropriately explained by other much commoner conditions. Finally, the natural history of the illnesses reported in this family is as atypical for variegate porphyria as are their symptoms.

Identification and characterisation of a deletion (537delAT) in the protoporphyrinogen oxidase gene in a South African variegate porphyria family

Variegate porphyria is an autosomal dominant disorder of haem metabolism resulting from a partial decrease in protoporphyrinogen oxidase activity. Variegate porphyria is highly prevalent in South Africa, the result of a founder effect now confirmed genetically as a single point mutation (R59W) which has been described in nearly all South African variegate porphyria patients studied. Only two other mutations (H20P, R168C) have been reported in South Africa. We utilised simultaneous, single‐stranded conformational polymorphism and heteroduplex analysis, and direct sequencing to identify a further mutation; a 2 bp deletion in exon 6 which results in a premature stop codon 11 codons downstream from the mutation and is the first reported deletion in the protoporphyrinogen oxidase gene in a South African family. The familial segregation of this mutation strongly suggests that it is the disease causing mutation for variegate porphyria in this family. This further evidence for allelic heterogeneity limits the utility of tests for the R59W mutation in the diagnosis of variegate porphyria in South Africa. Hum Mutat 12:403–407, 1998.

The effect of oral activated charcoal on the course of congenital erythropoietic porphyria

Summary The administration or oral activated charcoal to two patients with congenital erythropoietic porphyria has previously been reported to result in a marked reduction in plasma and urinary porphyrin concentrations and in one case, clinical remission. We describe an additional case in which the use of charcoal was associated with an apparent exacerbation of the biochemical activity of the disease following an initial period of remission. This result is unexpected, and currently unexplained. We conclude that charcoal therapy in porphyria may not be without risk, and should be used with caution.

Hepatoerythropoietic porphyria precipitated by viral hepatitis.

Porphyria cutanea tarda (PCT), the condition resulting from a deficiency of hepatic uroporphyrinogen decarboxylase activity, is the commonest form of porphyria. Both acquired and familial form exist and are commonly associated in adults with liver disease and hepatic iron overload. The condition is extremely rare in children; most cases of childhood PCT are familial and some particularly severe cases have been shown to have a hepatoerythropoietic porphyria or homozygous uroporphyrinogen decarboxylase deficiency. A case is described of hepatoerythropoietic porphyria in which the disease was first precipitated at the age of two by a coincidental hepatitis A infection and improved as the hepatitis cleared. This paper reviews the evidence that viral hepatitis may precipitate overt PCT in children in a manner analogous to the precipitation of PCT in adults by alcohol associated liver disease.