Heme biosynthesis and the porphyrias

Porphyrias, is a general term for a group of metabolic diseases that are genetic in nature. In each specific porphyria the activity of specific enzymes in the heme biosynthetic pathway is defective and leads to accumulation of pathway intermediates. Phenotypically, each disease leads to either neurologic and/or photocutaneous symptoms based on the metabolic intermediate that accumulates. In each porphyria the distinct patterns of these substances in plasma, erythrocytes, urine and feces are the basis for diagnostically defining the metabolic defect underlying the clinical observations. Porphyrias may also be classified as either erythropoietic or hepatic, depending on the principal site of accumulation of pathway intermediates. The erythropoietic porphyrias are congenital erythropoietic porphyria (CEP), and erythropoietic protoporphyria (EPP). The acute hepatic porphyrias include ALA dehydratase deficiency porphyria, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP) and variegate porphyria (VP). Porphyria cutanea tarda (PCT) is the only porphyria that has both genetic and/or environmental factors that lead to reduced activity of uroporphyrinogen decarboxylase in the liver. Each of the 8 enzymes in the heme biosynthetic pathway have been associated with a specific porphyria (Table 1). Mutations affecting the erythroid form of ALA synthase (ALAS2) are most commonly associated with X-linked sideroblastic anemia, however, gain-of-function mutations of ALAS2 have also been associated with a variant form of EPP. This overview does not describe the full clinical spectrum of the porphyrias, but is meant to be an overview of the biochemical steps that are required to make heme in both erythroid and non-erythroid cells.

Congenital erythropoietic porphyria. A mild variant with low uroporphyrin I levels due to a missense mutation (A66V) encoding residual uroporphyrinogen III synthase activity

BACKGROUND AND DESIGN

Congenital erythropoietic porphyria, an inborn error of heme biosynthesis, results from the deficient activity of the enzyme uroporphyrinogen III synthase. The clinical manifestations in unrelated patients with this autosomal recessive disorder are remarkedly variable, ranging from mild cutaneous involvement to severe transfusion-dependent hemolytic anemia. Biochemical and molecular studies were undertaken to investigate the nature of the unusually mild phenotype in a 15-year-old boy with only cutaneous manifestations.

RESULTS

The proband's levels of total porphyrins, urinary uroporphyrin I, and erythrocyte coproporphyrin I were elevated, but not as dramatically as in other patients with this porphyria. Interestingly, the erythrocyte uroporphyrinogen III synthase activity in the proband was about 21% of the normal mean, indicating the presence of significant residual activity. In cultured lymphoblasts from the proband, his father, and mother, the enzymatic activities were 10%, 70%, and 50% of the normal mean, respectively. Molecular analyses revealed that the proband was heteroallelic for two uroporphyrinogen III synthase missense mutations: the C73R allele inherited from his mother and the A66V allele transmitted by his father. The A66V allele encoded residual enzymatic activity in vitro while the C73R allele did not.

CONCLUSIONS

The A66V allele accounted for the proband's low levels of porphyrin accumulation and mild clinical manifestations. Such genotype-phenotype correlations should provide understanding of the remarkable clinical variability in other patients with this inherited porphyria.

Congenital erythropoietic porphyria: identification and expression of exonic mutations in the uroporphyrinogen III synthase gene

Congenital erythropoietic porphyria (CEP), an inborn error of heme biosynthesis, results from the deficient activity of uroporphyrinogen III synthase (URO-synthase). This autosomal recessive disorder is heterogeneous; patients with severe disease are often transfusion dependent, while milder patients primarily have cutaneous involvement. To investigate this phenotypic heterogeneity, exonic point mutations in the URO-synthase gene were identified in unrelated CEP patients. Four missense mutations were identified: (a) an A to G transition of nucleotide (nt) 184 that predicted a Thr to Ala substitution at residue 62 (designated T62A); (b) a C to T transition of nt 197 that encoded an Ala to Val replacement at residue 66 (A66V); (c) a T to C transition of nt 217 that predicted a Cys to Arg substitution at residue 73 (C73R); and (d) a C to T transition of nt 683 that resulted in a Thr to Met replacement at residue 228 (T228M). In addition, a G to A transition of nt 27 that did not change the encoded amino acid (A9A) was detected in an African patient. The T62A, C73R, and T228M alleles did not express detectable enzymatic activity, while the A66V allele expressed residual, but unstable activity. The C73R allele was present in eight of 21 unrelated CEP patients (21% of CEP alleles). In three patients, identification of both alleles permitted genotype-phenotype correlations; the A66V/C73R, T228M/C73R, and C73R/C73R genotypes had mild, moderately severe, and severe disease, respectively. These findings provide the first genotype-phenotype correlations and permit molecular heterozygote detection in this inherited porphyria.

Heterogeneity of mutations in the uroporphyrinogen III synthase gene in congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) or Günther's disease is an inborn error of heme biosynthesis transmitted as an autosomal recessive trait and characterized by a profound deficiency of uroporphyrinogen III synthase (UROIIIS) activity. We have previously described two missense mutations in the UROIIIS gene, confirming that the primary defect responsible for CEP is a structural alteration of this gene. We have extended our work to 5 additional unrelated families. Two new point mutations, a deletion and an insertion have been found in the messenger RNA. Our study shows that a molecular heterogeneity of the mutations exists in Günther's disease. One mutation (C73R), however, appears to be more frequent than the others. Finally, the different normal and mutated proteins have been expressed in Escherichia coli to determine the consequence of the mutations on the enzyme activity.

Observation on bovine congenital erythrocytic protoporphyria in the blonde d'Aquitaine breed

Three blonde d'Aquitaine calves (one male and two females) about four months old, exhibited skin lesions just after birth, the site and nature of which suggested photosensitisation. Their porphyrin metabolism indicated a marked decrease in the activity of lymphocytic ferrochelatase, leading to a diagnosis of congenital erythrocytic protoporphyria. The associated nervous disorders of the 'recurrent epileptiform seizure' type are discussed in the light of complementary histological and biochemical tests.

[A case of congenital porphyria in a calf]

The case of a male calf affected with bovine congenital porphyria is reported in the present paper. The diagnosis was based on the specific and pathognomonic symptoms: lesions of the pale parts of the skin due to photosensitization, brownish discolouration of the teeth and urine, overall wasting and retardation of growth. The diagnosis was verified by analysis of the blood and urine: in the blood we found a high concentration of protoporphyrins (269 micrograms/l) and a rather low cell count (19 per cent), in the urine high concentrations of uro- and coproporphyrins (3340 and 2550 micrograms/l respectively) were determined. As there is no effective treatment for this disease, it was advised to keep the animal indoors and fatten it. The farmer did not follow this advice. The calf died within a few months.

Determination of hydroxy and peroxy acid derivatives of uroporphyrin in the plasma of patients with congenital erythropoietic porphyria by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method is described for the determination of hydroxy and peroxy acid derivatives of uroporphyrin in the plasma of patients with congenital erythropoietic porphyria. The porphyrins were extracted from the plasma with 20% trichloroacetic acid-dimethyl sulphoxide (1:1, v/v). The supernatant after centrifugation was chromatographed on a Hypersil-ODS column by gradient elution with 9% (v/v) acetonitrile in 1 M ammonium acetate buffer (pH 5.16) (solvent A) and 10% (v/v) acetonitrile in methanol (solvent B) as the gradient mixture. The method was also suitable for the preparative isolation of the porphyrins.

Bone-marrow transplantation for congenital erythropoietic porphyria

Congenital erythropoietic porphyria, a disorder of haem synthesis, is caused by uroporphyrinogen III synthase deficiency in bone-marrow normoblasts. Uroporphyrins and coproporphyrins accumulate and cause oxidative damage to cells exposed to sunlight. Uroporphyrin overproduction was greatly reduced and skin changes reversed in a girl who received a bone-marrow graft from an HLA-identical sibling at 10 years of age. The patient died 11 months after transplantation because of severe progressive pneumonitis and encephalopathy associated with cytomegalovirus infection, but the encouraging response up to 8 months after engraftment indicates a possible benefit of bone-marrow transplantation in the treatment of this rare but usually fatal inherited disease.

Identification of peroxyacetic acid uroporphyrin I in the urine of patients with congenital erythropoietic porphyria by liquid chromatography and mass spectrometry

A new porphyrin, peroxyacetic acid uroporphyrin I, has been isolated from the urine of patients with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The porphyrin was characterized by high resolution mass spectrometry and by typical chemical reactions of a peroxyacid.

The osteodystrophy of congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is a rare disorder of heme biosynthesis that results in the production of large quantities of photoactive porphyrins. The clinical syndrome is dominated by extreme photosensitivity with mutilation of light exposed extremities and hemolytic anemia. Bone disease has been occasionally noted, but is not well characterised. We describe a man with CEP who developed bone pain and spinal crush fractures at the age of 22. Skeletal radiographs revealed features typical of other severe hemolytic anemias, but in addition there was loss of the terminal phalanges of the hand as a result of photomutilation. Spinal bone density (assessed by DPA) was reduced and at the hip bone density was at the lower limit of normal. The metacarpal cortical bone density was 2.9 standard deviations below normal. Biochemical and histological studies accelerated bone turnover. Although the serum 250H vitamin D concentration was very low (because of light avoidance) there was no evidence that the bone disease was a consequence of this. Treatment for one year with clodronate and a high transfusion regime was associated with small reductions in serum alkaline phosphatase and urine hydroxyproline excretion, but there was no improvement in bone mineral density. We conclude that CEP has a distinctive osteodystrophy comprising osteolysis of light-exposed extremities and a high turnover type of osteoporosis. Privational vitamin D deficiency may also occur. The effect upon bone of the new therapies for CEP should be considered.

Rapid improvement in the chemical pathology of congenital erythropoietic porphyria with treatment with superactivated charcoal

Non-absorbable sorbents that bind porphyrins in the gastrointestinal tract may be useful in the treatment of porphyrias whose manifestations result from porphyrin excess. To test this, we assessed the effect of oral charcoal on porphyrin economy in a patient with a probable congenital erythropoietic porphyria. Treatment with a superactivated charcoal (Super Char), 25 g three times daily, was associated with a precipitous drop in erythrocyte porphyrin (from 21.4 +/- 2.9 [SD] to 7.4 +/- 0.4 nmole/ml; p less than 0.025) and plasma porphyrin (from 1.56 +/- 0.24 to 0.70 +/- 0.08 nmole/ml; p less than 0.01). Urinary porphyrin excretion appeared to rise, from 103 +/- 45 to 160 +/- 30 mumole/d, but the change was not statistically significant. Constipation appeared to limit compliance with the charcoal regimen by the end of the study period. Nonetheless, superactivated charcoal may be a useful therapy in this disfiguring porphyria.

Isolation and characterization of beta-hydroxypropionic acid- and hydroxyacetic acid-uroporphyrin I in the urine of a patient with congenital erythropoietic porphyria by high performance liquid chromatography and liquid secondary ion mass spectrometry

beta-Hydroxypropionic acid- and hydroxyacetic acid-uroporphyrin I have been isolated from the urine of a patient with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The compounds were characterized by their chemical behaviour and confirmed by liquid secondary ion mass spectrometry.

Coexistent hereditary coproporphyria and congenital erythropoietic porphyria (Günther disease)

We present data on one patient with an inheritance pattern for two porphyrias. From her mother she inherited the trait of hereditary coproporphyria; from both parents she inherited the trait of congenital erythropoietic porphyria (Günther disease). Enzyme studies confirmed this new type of dual porphyria.

Corneal and conjunctival changes in congenital erythropoietic porphyria

Penetrating keratoplasty and conjunctival resection were performed on a 53-year-old woman with confirmed congenital erythropoietic porphyria. Corneal and conjunctival tissue samples, studied by light and electron microscopy, revealed inflammatory cells and a reduced keratocyte population. Vessels within the conjunctival and corneal stroma displayed a thickened basement membrane. Microfibrillar material was seen in the extracellular spaces of the conjunctival stroma. These changes are similar to those reported for ultraviolet light-exposed skin of porphyria patients. The Descemet's membrane lacked the normal fetal and postnatal banding. It presented as a homogeneous layer, consisting of uniform, densely packed collagen fibers, which suggests endothelial damage in utero. The corneal endothelium was severely damaged.

The porphyrias

The porphyrias are a group of disorders of heme metabolism that result from partial defects in the several enzymes that control heme biosynthesis. Accumulation of porphyrins or porphyrin precursors in several different patterns results from these defects and biochemically characterizes each specific syndrome. Patterns of cutaneous photosensitivity and associated systemic symptoms among the several porphyrias result from the types of porphyrins or precursors accumulated in each.

Beta-carotene therapy for erythropoietic protoporphyria and other photosensitivity diseases

This paper describes the development of the use of carotenoid pigments in the treatment of light-sensitive skin diseases. It also discusses the animal and human studies involved in determining whether carotenoids have any anti-cancer activity. The possible mechanisms of carotenoid photoprotective and anti-cancer actions are briefly discussed.

Depletion of histidine and tryptophan serum levels in porphyria cutanea tarda and congenital erythropoietic porphyria patients after irradiation with visible light

We have studied the photosensitized oxidation, via singlet oxygen production, of histidine (His) and tryptophan (Trp) in the serum of porphyria patients and in the serum of healthy volunteers before or after addition of hematoporphyrin. It was observed that free plasma His and Trp are good probes of singlet oxygen production in the blood under visible light irradiation. However, Trp, which is mostly bound to serum albumin, is much less susceptible to photooxidation than His, which remains free in the plasma. These results must not be ignored in systemic effects of porphyrias and in photochemotherapy with hematoporphyrin derivatives.

Congenital erythropoietic porphyria. A case report with discussion of different porphyrin excretion patterns

A 5-year-old girl with the classical clinical features of congenital erythropoietic porphyria (CEP) is described. Different types of CEP are discussed based on varying excretion patterns of porphyrins.

Noninfectious skin diseases of cattle

The noninfectious bovine skin disorders can best be summarized by four factors: environmental, nutritional, congenital, and neoplastic. This article has attempted to address the etiology, treatment, and prevention of most of these noninfectious diseases.

[Acute intermittent porphyria]

Acute intermittent porphyria (AIP) is a congenital disease which as its name suggests, runs intermittently. Biochemically it is characterised by over-production of hepatic ALA synthetase (ALA-s), inducible mitochondrial enzyme and an increase in prophyrinic precursors (PBG, ac S-ALA). Clinically it is characterised by an abdominal nervous symptomatology. The primary metabolic error has been identified as a deficiency in enzyme activity which partially blocks haem biosynthesis. During the appearance of clinical manifestations, certain factors are present which have the capacity of inducing hepatic ALA-s production in vitro. Apart from some preventive measures treatment is mainly of symptomatology and complications. More recently the use of ALA-s inhibitors has been introduced.

Chemical and biochemical aspects of photosensitization in livestock and poultry

Certain synthetic and naturally occurring chemicals, particularly those found in some range plants, may interact with livestock and poultry in the presence of activating light to produce photosensitization. Such photosensitization may have serious implications for livestock producers as a result of causing reduced performance of and even death of affected animals. The mechanisms producing photosensitization in livestock and poultry are discussed in context with the chemical nature of major livestock photosensitizers. The possibility that photosensitizing agents for livestock may have toxicologic significance in humans consuming photoactive residues in meat or animal byproducts is considered.

Toxicologic aspects of photosensitization in livestock

Two types of plant-caused photosensitizations are recognized in livestock: 1) primary, wherein the phototoxic agent in the plant is ingested and reaches the skin chemically unchanged; and 2) secondary, wherein the phototoxic agent in the porphyrin phylloerythrin produced by chlorophyll degradation in ruminant stomachs. Phylloerythrin is normally excreted in bile but is allowed to reach the skin when hepatic damage interferes with the phylloerythrin-excreting mechanism. Primary photosensitizing plant toxins are few, whereas secondary photosensitizations can be caused by damage to the liver by a variety of plant and other toxins. Plants causing each type of photosensitization are discussed and clinical manifestations of the disease in livestock are summarized. Tetradymia species are one of the most economically important causes of phototoxicity in livestock. The etiology of this phototoxic syndrome in sheep and the importance of sagebrush species as preconditioning agents for phototoxicity are discussed.

Congenital erythropoietic porphyria (Günther's disease): enzymatic studies on two cases of late onset

Cosynthetase was measured in hemolysates of two patients with CEP that appeared in adulthood. The level of cosynthetase activity was found to be very low (mean 18% of normal), ruling out the hypothesis of heterozygous cases. Several obligatory heterozygous carrier were also studied in whom cosynthetase activity was found to be intermediate (mean 46.66% of normal) between the levels of normal controls and homozygous patients whereas PBG deaminase was always normal. The nature of the metabolic abnormality is undoubtedly a primary defect of the cosynthetase activity; some cases of late onset emphasize the heterogeneity of the disease.