Hepatic porphyrias in children

Clinically overt hepatic porphyria is uncommon in children. The autosomal dominant acute hepatic porphyrias, acute intermittent porphyria (AIP), variegate porphyria (VP) and hereditary coproporphyria (HCP), are rarely present before puberty. Identification of asymptomatic children who have inherited these disorders is an important aspect of the management of the disease in their families and requires either enzymatic or DNA methods. Homozygous variants of AIP, VP and HCP usually present in early childhood and have phenotypes of variable severity. Mutational analysis is currently elucidating the relationship between these disorders and their autosomal dominant counterparts. 5-Aminolaevulinate dehydratase deficiency porphyria is a rare, autosomal recessive acute porphyria that may present at any age. Two cutaneous hepatic porphyrias are seen in children. Porphyria cutanea tarda (PCT), although mainly an adult disease, has been reported in young children with the autosomal dominant (type II) form of the disorder. Hepatoerythropoietic porphyria usually develops before the age of 2 years; patients are homo- or heteroallelic for uroporphyrinogen decarboxylase mutations, at least one of which is known to cause type II PCT.     

Porphyrien – was ist gesichert?

Porphyrias are caused by enzyme defects of heme biosynthesis. According to their clinical presentation and to each affected pathway, they are categorized into acute and non-acute as well as hepatic and erythropoietic porphyrias. Acute hepatic porphyrias, e.g. acute intermittent porphyria (AIP), porphyria variegata (VP), hereditary coproporphyria (HCP) and 5?aminolevulinic acid dehydratase-deficient porphyria (ALADP) are characterized by accumulation of the porphyrin precursors 5?aminolevulinic acid (ALA) and porphobilinogen (PBG) that correlate with severe abdominal, psychiatric, neurological or cardiovascular symptoms. Additionally, skin photosensitivity can occur in VP and less frequently, in HCP. Decisive for the diagnosis of acute hepatic porphyrias are a >4-fold elevated urinary excretion of ALA in ALADP and ALA and PBG in all other acute porphyrias. First-line treatment of an acute porphyria attack includes intensive care with pain management, sufficient caloric supply, strict avoidance of porphyrinogenic drugs and elimination of other triggering factors. Heme therapy is indispensable in case of developing neurological symptoms and clinical worsening despite first-line measures. Non-acute porphyrias, mainly porphyria cutanea tarda (PCT), erythropoietic protoporphyria (EPP) and X?linked protoporphyria (XLP) display accumulation of porphyrins in the skin and/or liver resulting in photosensitivity up to possible liver damage. Patients with PCT benefit from iron depletion, low-dose chloroquine treatment and/or hepatitis C virus elimination. Afamelanotide is associated with better sunlight tolerance in patients with EPP and XLP. Moreover, innovative therapies that highly selectively address dysregulated steps of the heme biosynthetic pathway are currently under clinical trial.     

Porphyrias in Japan: Compilation of All Cases Reported through 2002

The first case of porphyria on record in Japan was a patient with congenital erythropoietic porphyria (CEP) reported by Sato and Takahashi in 1920. Since then until the end of December 2002, 827 cases of porphyrias have been diagnosed from characteristic clinical and/or laboratory findings (463 males, 358 females, and 6 of unknown sex). Essentially all inherited porphyrias have been found in Japan, with the incidences and clinical symptoms generally being similar to those reported for other countries. The male-female ratio was approximately 1:1 for CEP, whereas it was higher for erythropoietic protoporphyria. In contrast, preponderances of female patients exist with acute hepatic porphyrias, such as acute intermittent porphyria (AIP), variegate porphyria (VP), and hereditary coproporphyria (HCP), and with undefined acute porphyria. Although porphyria cutanea tarda (PCT) is believed to be increasing recently in women in other countries because of smoking and the use of contraceptives, it is still by far more prominent in males in Japan than in females. The recent increasing contribution of hepatitis C virus infection to PCT in Japan has also been recognized. but there have been no PCT cases in Japan with HFE gene mutations. Familial occurrence and consanguinity were high for CEP, as expected; however, significant consanguinity was also noted in families where CEP, AIP, HCP, VP, or PCT occurred as a single isolated case without a family history of disease. This survey also revealed that as many as 71% of acute hepatic porphyria cases were initially diagnosed as nonporphyria and later revised or corrected to porphyria, indicating the difficulty of diagnosing porphyria in the absence of specific laboratory testing for porphyrins and their precursors in urine, stool, plasma, and erythrocyte samples.     

The porphyrias.

The heterogeneous group of diseases called the porphyrias may all be characterised by derangement of specific stages in the haem biosynthetic pathway. In the acute porphyrias; acute intermittent porphyria, urophorphyrinogen 1 synthase, hereditary coproporphyria, coproporphyrinogen oxidase and variegate porphyria, ferrochelatase or protoporphyrinogen oxidase, are the enzymes affected, whilst in the non acute porphyrias, cutaneous hepatic porphyria, uroporphyrinogen decarboxylase, congenital porphyria, uroporphyrinogen cosynthase; and erythropoietic protoporphyria; ferrochelatase are the enzymes affected. In each of the porphyrias, the activity of the initial and rate controlling enzyme of the pathway, delta-aminolaevulinic acid synthase is raised which constitutes the principal control point of the pathway. Secondary control in each of these diseases lies at the leve of uroporphyrinogen 1 synthase. As a consequence of this secondary control, there is excessive excretion of the porphyrin precursors delta-aminolaevulinic acid and porphobilinogen in the acute porphyrias and excessive excretion of porphyrins leading to solar photosensitivity in the non-acute porphyrias and in variegate and hereditary coproporphyria. There are a number of secondary metabolic aspects in the porphyrias, such as the role of steroid metabolism; the influence of drugs in the potentiation of attacks; and the potential for the pathway to branch at stages prior to porphyrin formation which result in the synthesis of various monopyrroles. The therapy of the two groups of porphyrias are quite different. Prophylaxis is important in both types but is particularly important in the avoidance of various drugs in the acute porphyrias. The acute attack may be specifically treated with carbohydrates, beta-blockers and haematin. Cutaneous hepatic porphyria may be treated by venesection, erythropoietic protoporphyria with beta caratene whilst congenital porphyria may be improved by splenectomy and chloroquine therapy.     

Prognosis of acute porphyria: occurrence of acute attacks, precipitating factors, and associated diseases.

We evaluated the prognosis of acute porphyria among 206 adult Finnish patients with acute intermittent porphyria (AIP) or variegate porphyria (VP). The series represents all known patients with these porphyrias in Finland. Of the 47 patients who had a total of 117 acute attacks during the period 1967-1989, 6 died during an attack and 21 attacks were associated with paresis; the frequency of severe attacks was significantly smaller than before 1967 (p = 0.00002). Most pareses and deaths occurred because of a delay in diagnosis and inappropriate treatment of porphyria. For those patients who were symptom-free at the time of diagnosis (1365 follow-up years), the risk of the first subsequent attack was significantly smaller than for those who had had an acute attack before the diagnosis of porphyria (1047 follow-up years, p = 0.005). In addition, milder symptoms of porphyria were more common among those who had had previous attacks than among those who had not (p less than 0.00001). In AIP the risk of attacks correlated with the excretion of porphobilinogen in the urine during remission among adults (p = 0.03); a low rate of excretion predicted freedom from acute attacks. A regular use of many precipitating drugs was never associated with symptoms of porphyria. Two percent of the surgical operations and 4% of the pregnancies were associated with acute attacks. Nearly one-third of the women had symptoms of porphyria associated with the menstrual cycle, but these seldom proceeded to an acute attack. Forty-six percent of the women had used sex-hormone preparations regularly; 2 of them (4.5%) experienced associated acute attacks. Patients with AIP or VP showed increased incidences of hepatocellular carcinoma, and probably also chronic renal failure and hypertension.     

Erythropoietic and hepatic porphyrias

Porphyrias are divided into erythropoietic and hepatic manifestations. Erythropoietic porphyrias are characterized by cutaneous symptoms and appear in early childhood. Erythropoietic protoporphyria is complicated by cholestatic liver cirrhosis and progressive hepatic failure in 10% of patients. Acute hepatic porphyrias (-aminolaevulinic acid dehydratase deficiency porphyria, acute intermittent porphyria, hereditary coproporphyria and variegate porphyria) are characterized by variable extrahepatic gastrointestinal, neurological–psychiatric and cardiovascular manifestations requiring early diagnosis to avoid life-threatening complications. Acute hepatic porphyrias are pharmacogenetic and molecular regulatory diseases (without porphyrin accumulation) mainly induced by drugs, sex hormones, fasting or alcohol. The disease process depends on the derepression of hepatic -aminolaevulinic acid synthase following haem depletion. In contrast to the acute porphyrias, nonacute, chronic hepatic porphyrias such as porphyria cutanea tarda are porphyrin accumulation disorders leading to cutaneous symptoms associated with liver disease, especially caused by alcohol or viral hepatitis. Alcohol, oestrogens, haemodialysis, hepatitis C and AIDS are triggering factors. Porphyria cutanea tarda is the most common porphyria, followed by acute intermittent porphyria and erythropoietic protoporphyria. The molecular genetics of the porphyrias is very heterogenous. Nearly every family has its own mutation. The mutations identified account for the corresponding enzymatic deficiencies, which may remain clinically silent throughout life. Thus, the recognition of the overt disorder with extrahepatic manifestations depends on the demonstration of biochemical abnormalities due to these primary defects and compensatory hepatic overexpression of hepatic -aminolaevulinic acid synthase in the acute porphyrias. Consequently, haem precursors are synthesized in excess. The increased metabolites upstream of the enzymatic defect are excreted into urine and faeces. The diagnosis is based on their evaluation. Primary enzymatic or molecular analyses are noncontributary and may be misleading. Acute polysymptomatic exacerbations accompany a high excretory constellation of porphyrin precursors -aminolaevulinic acid and porphobilinogen. Homozygous or compound heterozygous variants of acute hepatic porphyrias may already manifest in childhood.     

Pro-oxidant and antioxidant factors in acute intermittent porphyria: Family studies

Given the crucial role of iron and porphyrins in oxidative cellular damage in the chronic porphyrias, we undertook an extensive study in families with acute porphyrias to evaluate the possible role of similar oxidative damage in these diseases, whose natural history is often also complicated by neoplastic evolution. Four unrelated patients with acute intermittent porphyria (AIP) were studied together with 37 members of four different families. Aminolevulinic acid and porphobilinogen were measured in urine, and porphyrins in urine, plasma and stools. The activity of the congenitally deficient enzyme, porphobilinogen deaminase, and the concentrations of plasma iron, transferrin, ferritin, and various antioxidants (ascorbic acid, retinol, tocopherol, alpha- and beta-carotene, by a personal HPLC method) and the urinary and plasma metabolites of nitrous oxide were also assayed. The results showed no relationship between the observed increase of porphyrin metabolites and the presence of markers of oxidative damage or the decrease of circulating antioxidants: however, when such a decrease was registered, it depended on spontaneous or iatrogenic iron accumulation. We conclude that family screening, recommended for the identification of AIP carriers, must also include evaluation of iron stores with a view to preventing the oxidative damage and in order to forestall the neoplastic evolution of the disease.     

Porphyrien

Porphyrias are metabolic disorders of the heme biosynthesis. Clinically, they can be differentiated into acute and non-acute porphyrias. The symptomatic phase of acute hepatic porphyrias is characterized by overproduction of neurotoxic porphyrin precursors and porphyrins. Acute intermittent porphyria, Variegate porphyria, Hereditary coproporphyria and Doss porphyria belong to this group of metabolic disorders. The clinical presentation of the acute hepatic porphyria syndrome includes abdominal, psychiatric, neurological and cardiovascular symptoms. The diagnosis is based on a tenfold increased urinary excretion of porphobilinogen (apart from Doss porphyria). Besides symptomatic therapy with non-porphyrinogenic drugs, electrolyte compensation and intensive monitoring, intravenous administration of glucose and heme arginate is established for treatment. Among the non-acute types like Porphyria cutanea tarda, Erythropoietic protoporphyria and Congenital erythropoietic porphyria, the accumulated porphyrins cause photosensitivity of the skin up to severe liver damage. The location of the deficient enzyme within the heme biosynthesic pathway determines the pattern of the accumulated porphyrins. Besides light protection, there are different therapies depending on the type of non-acute porphyria. Ultimately, liver transplantation may be considered in therapy-resistant cases of acute hepatic porphyrias and bone marrow transplantation in severe cases of erythropoietic porphyrias.     

The incidence of inherited porphyrias in Europe

Retrospective estimates of the prevalence of porphyrias have been reported but there has been no large scale prospective study of their incidence. The European Porphyria Network collected information prospectively over a 3 year period about the number of newly diagnosed symptomatic patients with an inherited porphyria (335 patients from 11 countries). Prevalence was calculated from the incidence and mean disease duration. The incidence of hepato-cellular carcinoma (HCC) in acute hepatic porphyria and the prevalence of patients with recurrent acute attacks of porphyria were also investigated. The incidence of symptomatic acute intermittent porphyria (AIP) was similar in all countries (0.13 per million per year; 95 % CI: 0.10 – 0.14) except Sweden (0.51; 95 % CI: 0.28–0.86). The incidence ratio for symptomatic AIP: variegate porphyria: hereditary coproporphyria was 1.00:0.62: 0.15. The prevalence of AIP (5.4 per million; 95 % CI: 4.5–6.3) was about half that previously reported. The prevalence of erythropoietic protoporphyria (EPP) was less uniform between countries and, in some countries, exceeded previous estimates. Fourteen new cases of HCC (11 from Sweden) were reported in patients with acute porphyria. Sixty seven patients (3 VP; 64 AIP: 53 females, 11 males) with recurrent attacks of acute porphyria were identified. The estimated percentage of patients with AIP that will develop recurrent acute attacks was 3–5 %. In conclusion, the prevalence of symptomatic acute porphyria may be decreasing, possibly due to improved management, whereas the prevalence of EPP may be increasing due to improved diagnosis and its greater recognition as a cause of photosensitivity.     

Porphyrias

Porphyrias are metabolic disorders of the heme biosynthesis. Clinically, they can be differentiated into acute and non-acute porphyrias. The symptomatic phase of acute hepatic porphyrias is characterized by overproduction of neurotoxic porphyrin precursors and porphyrins. Acute intermittent porphyria, Variegate porphyria, Hereditary coproporphyria and Doss porphyria belong to this group of metabolic disorders. The clinical presentation of the acute hepatic porphyria syndrome includes abdominal, psychiatric, neurological and cardiovascular symptoms. The diagnosis is based on a tenfold increased urinary excretion of porphobilinogen (apart from Doss porphyria). Besides symptomatic therapy with non-porphyrinogenic drugs, electrolyte compensation and intensive monitoring, intravenous administration of glucose and heme arginate is established for treatment. Among the non-acute types like Porphyria cutanea tarda, Erythropoietic protoporphyria and Congenital erythropoietic porphyria, the accumulated porphyrins cause photosensitivity of the skin up to severe liver damage. The location of the deficient enzyme within the heme biosynthesic pathway determines the pattern of the accumulated porphyrins. Besides light protection, there are different therapies depending on the type of non-acute porphyria. Ultimately, liver transplantation may be considered in therapy-resistant cases of acute hepatic porphyrias and bone marrow transplantation in severe cases of erythropoietic porphyrias.     

Acute Hepatic Porphyria

The porphyrias comprise a set of diseases, each representing an individual defect in one of the eight enzymes mediating the pathway of heme synthesis. The diseases are genetically distinct but have in common the overproduction of heme precursors. In the case of the acute (neurologic) porphyrias, the cause of symptoms appears to be overproduction of a neurotoxic precursor. For the cutaneous porphyrias, it is photosensitizing porphyrins. Some types have both acute and cutaneous manifestations. The clinical presentation of acute porphyria consists of abdominal pain, nausea, and occasionally seizures. Only a small minority of those who carry a mutation for acute porphyria have pain attacks. The triggers for an acute attack encompass certain medications and severely decreased caloric intake. The propensity of females to acute attacks has been linked to internal changes in ovarian physiology. Symptoms are accompanied by large increases in delta-aminolevulinic acid and porphobilinogen in plasma and urine. Treatment of an acute attack centers initially on pain relief and elimination of inducing factors such as medications; glucose is administered to reverse the fasting state. The only specific treatment is administration of intravenous hemin. An important goal of treatment is preventing progression of the symptoms to a neurological crisis. Patients who progress despite hemin administration have undergone liver transplantation with complete resolution of symptoms. A current issue is the unavailability of a rapid test for urine porphobilinogen in the urgent-care setting.     

Variegate porphyria in a 46‐year‐old patient taking sibutramine for weight loss

The acute hepatic porphyrias can cause life‐threatening attacks of neurovisceral symptoms that mimic other acute medical conditions. Variegate porphyria caused by mutations in the protoporphyrinogen oxidase (PPOX) gene is a latent disorder characterized by exacerbations induced by fasting, alcohol consumption or certain drugs. We describe the case of a 46‐year‐old female patient presenting with a first episode of symptomatic porphyria after 10 d of sibutramine treatment for weight loss. Genetic analysis showed a heterozygous R168H hot spot mutation in the PPOX gene. A putative effect of sibutramine on the hepatic haem biosynthetic pathway and reduced food intake have likely caused this exacerbation of a porphyria attack. Although this may be the first case report of this kind, the risk of acute porphyria should be considered in patients using pharmacotherapy for obesity.     

Does paraneoplastic porphyria cutanea tarda exist?

Our investigations in 134 patients showed corresponding to literature porphyria cutanea tarda (PCT) diagnosed by biochemical methods not to be a paraneoplastic dermatosis (but one possible exception acquainted). Relations between PCT and extrahepatic non-porphyrin producing tumours are improbable. Nevertheless but extremely seldom an irregular urinary porphyrin excretion associated with cutaneous changes of hepatic porphyria should lead to the presumption of a porphyrin producing hepatoma. PCT lasting for decades apparently presents a higher frequency of hepatocellular carcinoma in patients suffering from liver cirrhosis than in cirrhotics without PCT. It is supposed that this possible progredience of liver disease in PCT into hepatocellular carcinoma may be prevented by chloroquine phosphate therapy.     

RNAi-mediated silencing of hepatic Alas1 effectively prevents and treats the induced acute attacks in acute intermittent porphyria mice

The acute hepatic porphyrias are inherited disorders of heme biosynthesis characterized by life-threatening acute neurovisceral attacks. Factors that induce the expression of hepatic 5-aminolevulinic acid synthase 1 (ALAS1) result in the accumulation of the neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), which recent studies indicate are primarily responsible for the acute attacks. Current treatment of these attacks involves i.v. administration of hemin, but a faster-acting, more effective, and safer therapy is needed. Here, we describe preclinical studies of liver-directed small interfering RNAs (siRNAs) targeting Alas1 (Alas1-siRNAs) in a mouse model of acute intermittent porphyria, the most common acute hepatic porphyria. A single i.v. dose of Alas1-siRNA prevented the phenobarbital-induced biochemical acute attacks for approximately 2 wk. Injection of Alas1-siRNA during an induced acute attack significantly decreased plasma ALA and PBG levels within 8 h, more rapidly and effectively than a single hemin infusion. Alas1-siRNA was well tolerated and a therapeutic dose did not cause hepatic heme deficiency. These studies provide proof-of-concept for the clinical development of RNA interference therapy for the prevention and treatment of the acute attacks of the acute hepatic porphyrias.The acute hepatic porphyrias are caused by the deficient activities of specific enzymes in the heme biosynthetic pathway and include three autosomal dominant diseases—acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP)—and the autosomal recessive 5-aminolevulinic acid dehydratase deficiency porphyria (ADP) (1). These inherited metabolic disorders are characterized by life-threatening acute neurovisceral attacks that include severe abdominal pain, hypertension, tachycardia, constipation, motor weakness, seizures, and paralysis (1). Various factors, including cytochrome P450 (CYP)-inducing drugs, dieting, and hormonal changes precipitate the acute attacks by increasing the expression of hepatic 5-aminolevulinic acid synthase (ALAS1), the first and rate-limiting enzyme of the heme biosynthetic pathway (2–6). When hepatic ALAS1 is induced, the respective enzyme deficiencies create a metabolic bottleneck, thereby decreasing hepatic heme production and depleting the “free” heme pool. This leads to the loss of the negative feedback inhibition of heme on ALAS1 (7–9) and, consequently, further up-regulation of hepatic ALAS1 expression. As hydroxymethylbilane synthase (HMBS)—the third enzyme in the heme biosynthetic pathway—is less abundant in comparison with the other heme biosynthetic enzymes (10), it becomes rate-limiting when ALAS1 is markedly increased. As a result, the neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG) are overproduced in the liver and are markedly accumulated in the plasma and urine during the acute attacks (only ALA accumulates in ADP).Currently, the standard therapy for the acute neurovisceral attacks is the i.v. administration of hemin, which provides exogenous heme for the negative feedback inhibition of ALAS1, thereby decreasing ALA and PBG production (11–13). Although patients generally respond well, its effect is slow, typically requiring three to four daily infusions to normalize the elevated plasma and urinary ALA and PBG concentrations (14). Patients who experience recurring attacks are treated prophylactically with weekly to monthly hemin infusions, which are associated with side effects such as phlebitis and iron overload (15). Thus, an alternative therapeutic approach for the acute hepatic porphyrias that is more effective, faster-acting, and safer is desirable.Previously, the pathogenic mechanism of the acute neurovisceral attacks was unclear, particularly whether the attacks were due to the neurotoxic effects of the accumulated ALA and/or PBG or to the heme deficiency in neuronal tissues (16). However, nonporphyric liver transplant recipients who received livers from AIP patients (i.e., “domino” liver transplants) developed acute porphyric attacks despite their presumably normal neuronal heme levels, which demonstrated that the primary pathogenic mechanism is not neuronal heme deficiency but rather the effects of the neurotoxic hepatic metabolites ALA and/or PBG (17). Consistent with this finding, orthotopic liver transplantation in AIP patients and a VP patient with recurrent and incapacitating attacks resulted in the rapid normalization of ALA and PBG levels and the abrupt remission of attacks (18–20). Thus, the liver is the primary site of pathology in the acute hepatic porphyrias, and therapies designed to inhibit the induced overexpression of ALAS1 and the resulting elevation of ALA and PBG would prevent or treat the acute attacks in all four acute hepatic porphyrias.Here, we report preclinical studies of a liver-directed RNA interference (RNAi) therapy using an i.v.-administered small interfering RNA (siRNA) specific for the Alas1 mRNA (designated Alas1-siRNA). To identify a potent Alas1-siRNA, a panel of siRNAs targeting Alas1 was initially screened for their ability to inhibit Alas1 mRNA expression in cultured hepatic cells. The most active compounds were formulated into lipid nanoparticles (LNPs) for efficient hepatic delivery (21–23) and evaluated for their ability to down-regulate hepatic Alas1 mRNA expression in wild-type mice. The selected Alas1-siRNA was then evaluated in the mouse model for AIP for its effectiveness to prevent or treat an induced acute attack. These mice have ∼30% of wild-type HMBS activity and slightly elevated baseline plasma and urinary ALA and PBG levels (24). When phenobarbital (PB), a potent inducer of ALAS1 expression, is administered, ALA and PBG are markedly increased (20- to 30-fold and 40- to 90-fold in plasma, respectively), mimicking the biochemical pathology of a human acute attack (1, 24). Prophylactic administration of Alas1-siRNA in the AIP mice completely prevented the PB-induced accumulation of plasma and urinary ALA and PBG, whereas infusion of Alas1-siRNA after induction of an acute attack rapidly and effectively decreased the markedly elevated plasma ALA and PBG.     

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.     

Molecular mechanisms of dominant expression in porphyria

Summary Summary:#Partial deficiency of enzymes in the haem synthetic pathway gives rise to a group of seven inherited metabolic disorders, the porphyrias. Each deficiency is associated with a characteristic increase in haem precursors that correlates with the symptoms associated with individual porphyrias and allows accurate diagnosis. Two types of clinical presentation occur separately or in combination; acute life-threatening neurovisceral attacks and/or cutaneous symptoms. Five of the porphyrias are low-penetrance autosomal dominant conditions in which clinical expression results from additional factors that act by increasing demand for haem or by causing an additional decrease in enzyme activity or by a combination of these effects. These include both genetic and environmental factors. In familial porphyria cutanea tarda (PCTF), environmental factors that include alcohol, exogenous oestrogens and hepatotropic viruses result in inhibition of hepatic enzyme activity via a mechanism that involves excess iron accumulation. In erythropoietic protoporphyria (EPP), co-inheritance of a functional polymorphism in trans to a null ferrochelatase allele accounts for most clinically overt cases. In the autosomal dominant acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, hereditary coproporphyria), acute neurovisceral attacks occur in a minority of those who inherit one of these disorders. Although various exogenous (e.g. drugs, alcohol) and endogenous factors (e.g. hormones) have been identified as provoking acute attacks, these do not provide a full explanation for the low penetrance of these disorders. It seems probable that genetic background influences susceptibility to acute attacks, but the genes that are involved have not yet been identified.     

Liver cirrhosis induced by porphyria cutanea tarda: a case report and review

Porphyria cutanea tarda (PCT) is a metabolic disorder that results in a decrease in uroporphyrinogen decarboxylase activity. It is characterized by photosensitivity, bullae formation, and skin pigmentation. There are four types of PCT: acquired, familial, toxic, and hepatoerythropoietic. Uroporphyrin levels are elevated in the urine of PCT patients. PCT can be differentiated from other porphyrias by its clinical characteristics and the porphyrin levels in the serum, erythrocytes, urine, and feces. This metabolic disorder can lead to liver dysfunction as well as histological changes such as fatty infiltration or hepatic fibrosis. PCT rarely manifests as liver cirrhosis. We report herein a case of PCT-induced liver cirrhosis that progressed to hepatic failure.     

The neurological manifestations of porphyria: a review.

The hereditary hepatic porphyrias, PV, AIP and HC, are characterized biochemically by increased excretion of porphyrins and the porphyrin precursors ALA and PBG. They are characterized clinically by episodes of acute neurological involvement. The increased production of porphyrins and porphyrin precursors has been shown to be due to partial enzyme blocks along the heme biosynthetic pathway which results in secondary depression of the key enzyme ALA-synthetase. The neurological manifestations could therefore be related to either a decrease in essential heme-proteins or other heme-containing compounds within the nervous system, or to a toxic effect of the over-production of the porphyrin precursors ALA and PBG. There is evidence for and against both theories. Recent work from a number of research groups has shown the porphyrin precursors to have potent pharmacological effects on the nervous system, and these are possibly related to the GABA receptor and binding site-porphyrin precursor interactions. Current studies on therapy of the acute attack have concentrated on suppression of ALA-synthetase activity, and consequently, on reduced ALA and PBG production. A number of such methods of therapy have met with remarkable success and hold promise for the future treatment of the acute attack.     

Urinary Porphyrins in Liver Disease

By use of quantitative thin-layer chromatography, urinary porphyrins were examined in 40 healthy volunteers, 38 patients with porphyria cutanea tarda (PCT), and 139 patients with various liver diseases. Significant elevations not only of coproporphyrin but also of some other porphyrins were found in many patients with liver disease. However, there was no evident relationship between porphyrin disturbances and functional or clinical findings, and all of these non-PCT patients who initially demonstrated intense uroporphyrinuria, when re-studied apparently had more normal porphyrin excretion. It seems, therefore, that whereas porphyrin estimations are useful in porphyrias, no clinically important conclusions can be drawn from urinary findings in patients with liver disease. The origin of defective haem biosynthesis in liver disease remains obscure. It can only be speculated that transient and reversible urocoproporphyrinuria may occur in patients with defective hepatic uroporphyrinogen decarboxylase activity who clinically and biochemically are not porphyric.     

Acute intermittent porphyria

Acute intermittent porphyria (AIP) is characterised by neurovisceral crises the most common clinical presentation of which is abdominal pain. It is an autosomal dominant condition with incomplete penetrance and is potentially life-threatening. The key point in management is to suspect and confirm the diagnosis as early as possible in order to treat the attack and to avoid inappropriate treatments which may exacerbate the crisis. In this chapter we briefly outline the haem biosynthetic pathway and how deficiencies in individual enzymes give rise to the different porphyrias. We then describe the clinical features and diagnosis of AIP, followed by a discussion of pathogenesis, highlighting advances in the molecular biology of AIP and introducing the debate as to whether neurovisceral crises might result from porphyrin precursor neurotoxicity or from haem deficiency. Finally we discuss management, including family screening, avoidance of triggering factors, analgesia, maintenance of a high calorie intake, and administration of haem derivatives.