Heme biosynthesis in sideroblastic anemia

Vascular changes in erythropoietic protoporphyria: histopathologic and immunohistochemical study

BACKGROUND

Erythropoietic protoporphyria (EPP) is an inherited disease caused by deficient activity of ferrochelatase in the heme biosynthetic pathway. Accumulation of protoporphyrins and light exposure results in acute phototoxic skin reactions. The histopathologic findings of the light-exposed skin are thickening of the superficial dermal vessel walls and amorphous deposits around the vessels, but the origin and detailed composition of the perivascular material have been unclear.

OBJECTIVE

The vascular morphology and composition of the perivascular material were studied in the skin samples of patients with EPP.

METHODS

Skin biopsy specimens of 8 patients with EPP representing 7 Finnish EPP families with different genotypes were studied by means of light and electron microscopy and immunohistochemical methods.

RESULTS

The characteristic finding was thickened, periodic acid-Schiff-positive vessel walls caused by concentric reduplication of basal lamina and excess of fine granular material at the basal membrane zone in the superficial dermis. The perivascular deposits in the vicinity of vessel walls had a homogeneous or fine granular appearance without filaments. Direct immunofluorescence showed constant IgG deposits together with IgA, IgM, and C3 in the vessel walls. In immunohistochemistry, collagen IV and laminin could be demonstrated at the vascular basal membrane together with serum amyloid P protein, kappa and lambda light chains, and a 90-kd glycoprotein.

CONCLUSION

The vascular involvement indicates that the blood vessel walls in the papillary dermis are the primary tissues affected during an acute photoreaction. The repeated acute damage and repair processes in the basement membrane zone result in thickening of the vessel walls. Perivascular deposits are a secondary and irreversible phenomenon resulting from the leakage and accumulation of different serum components. These changes were not found in the nonexposed skin, indicating that an increased level of erythrocyte protoporphyrin per se is not responsible for the cutaneous manifestations, but the interaction of solar radiation is mandatory. Amorphous deposits distinguish EPP from variegate porphyria and porphyria cutanea tarda; a histopathologic examination may be a helpful tool in differentiating porphyric and nonporphyric photosensitivity.

Four novel mutations in the ferrochelatase gene among erythropoietic protoporphyria patients

A novel mutation was identified by direct sequencing of genomic polymerase chain reaction products in each of four Finnish erythropoietic protoporphyria families. All four mutations, including two deletions (751delGAGAA and the first de novo mutation, 1122delT) and two point mutations (286C-->T and 343C-->T), resulted in a dramatically decreased steady-state level of the allelic transcript, since none of the mutations could be demonstrated by direct sequencing of the amplified cDNAs synthesized from total RNA extracted from patients' lymphoblast cell lines. Because the assays of the ferrochelatase activity and erythrocyte protoporphyrin identify asymptomatic patients poorly, the DNA-based demonstration of a mutation is the only reliable way to screen individuals for the disease-associated mutation.

Myopathy, lactic acidosis, and sideroblastic anemia: a new syndrome

We describe 2 sibs (brother and sister) with myopathy, sideroblastic anemia, lactic acidosis, mental retardation, microcephaly, high palate, high philtrum, distichiasis, and micrognathia. Very low levels of cytochromes a, b, and c were detected in the patients' muscle mitochondria. Deposition of iron within the mitochondria of bone marrow erythroblasts was observed on electron microscopy. Irregular and enlarged mitochondria with paracrystalline inclusions were also seen on electron microscopy of the patients' muscle specimen. Examination of DNA from the affected sibs showed no deletions in the mitochondrial DNA nor the mutations identified in the syndromes of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) or myoclonus, and epilepsy associated with rugged-red fibers (MERRF). Since the parents were first cousins and 2 of 6 sibs (male and female) were affected, we suggest that the syndrome expressed by our patients represents a previously unknown autosomal recessive disorder that includes mitochondrial myopathy, lactic acidosis, and sideroblastic anemia.

Sustained high plasma 5-aminolaevulinic acid concentration in a volunteer: no porphyric symptoms

The pathogenesis of the acute porphyric attack is not known. One hypothesis is that porphyrin precursors, especially 5-aminolaevulinic acid (ALA), are toxic for neuronal tissue. This was tested by infusing ALA in a male volunteer after a loading dose at a rate of 50-80 mg h-1 for 92.5 h. During the experiment plasma ALA concentration was 9-11 mumol 1-l and porphobilinogen concentration 3-6 mumol 1-l which are the levels seen during acute attacks. Urinary excretion of these porphyrin precursors was also markedly increased. ALA infusion caused no subjective symptoms and no change in pulse rate, blood pressure, or autonomic nerve function or conduction velocity of peripheral nerves. Photosensitivity was not demonstrable. It is concluded that sustained high plasma ALA concentration does not cause porphyria-like symptoms.

Homozygous variegate porphyria. A severe skin disease of infancy

A boy exhibited severe bullous skin disease a few days after birth, followed by increased fragility of the exposed skin in spring and summer. Examination at 2 1/2 years of age led to characteristic biochemical findings: increased excretion of fecal porphyrins (coproporphyrin 121 to 131 and protoporphyrin 467 to 576 nmol/g dry weight), and increased erythrocyte protoporphyrin concentration (3643 to 4840 nmol/l). Lymphocyte protoporphyrinogen oxidase activity was very low in the patient (0.4 nmol/mg protein/h) and half-normal (2.7 and 2.3 nmol/mg protein/h) in the parents, suggesting that the patient had homozygous variegate porphyria. Severe skin symptoms and a high concentration of red cell protoporphyrin concentration in an infant should prompt suspicion of homozygous acute hepatic porphyria.

Impaired heme synthesis in a family with Pelger-Huët anomaly, recurrent abdominal pain attacks and impaired neutrophil motility in vitro

Heme synthesis was studied by measuring the activity of delta-aminolevulinic acid synthase (AmLev synthase) in granulocytes, the activity of delta-aminolevulinic acid dehydratase (AmLev dehydratase) and of uroporphyrinogen I synthase in erythrocytes as well as the concentrations of coproporphyrin and protoporphyrin in erythrocytes of 6 patients with Pelger-Huët anomaly. 3 of these patients from the same kindred had a syndrome of recurrent attacks of fever and abdominal pains, a tendency to skin infections, delayed wound healing and impaired neutrophil motility. The other 3 patients were asymptomatic. The activity of AmLev synthase was depressed in all 3 symptomatic patients and normal in the asymptomatic patients. 1 symptomatic patient had a decreased erythrocyte protoporphyrin concentration. These findings indicate a derangement of heme synthesis in the symptomatic patients. Their abdominal pain attacks could be due to heme depletion. The findings suggest that the abdominal pains of patients with porphyria could be due to decreased heme synthesis rather than due to accumulation of porphyrin precursors in tissues. The cause of the impaired neutrophil motility may be a defect in energy metabolism due to decreased supply of heme for oxidative metabolism.

Hereditary sideroblastic anaemia and autosomal inheritance of erythrocyte dimorphism in a Dutch family

Size distribution curves of red blood cells were used to detect the presence of microcytes in peripheral blood of members of a Dutch family with hereditary sideroblastic anaemia. 22 of 49 members of this family have a bimodal erythrocyte volume distribution curve and a dimorphic blood picture. The pattern of inheritance of this morphological abnormality is clearly autosomal. It is suggested that the study of red blood cell size distribution curves may add valuable information on the pattern of inheritance in other families with hereditary sideroblastic anaemia.

Variant of acute intermittent porphyria with normal erythrocyte uroporphyrinogen-I-synthase activity

A kindred in which several members have otherwise typical acute intermittent porphyria but normal erythrocyte uroporphyrinogen-I-synthase activity has been described from Finland. We studied two porphyric members of this kindred, two patients with typical acute intermittent porphyria, and two healthy controls using the delta-aminolaevulinic acid loading test and by measuring the erythrocyte enzymes of haem biosynthesis. The excretion pattern of haem precursors after the delta-aminolaevulinic loading test in the members of the kindred studied, was similar to that in typical acute intermittent porphyria suggesting an identical enzyme defect in the liver. The activity of all red cell enzymes studied was normal in the members of the kindred. The results suggest that porphyria in the kindred studied is a variant of acute intermittent porphyria, where the uroporphyrinogen-I-synthase defect is manifested in the liver but not in red cells.

Haem biosynthesis in refractory sideroblastic anaemia associated with the preleukaemic syndrome

The activities of 5 enzymes of the haem biosynthetic pathway and the protoporphyrin concentrations have been measured in peripheral red blood cells of 23 patients having a preleukaemic syndrome with refractory sideroblastic anaemia. A decreased delta-aminolaevulinic acid synthase (ALA-S) activity, an increased uroporphyrinogen I synthase activity and an increased red cell protoporphyrin concentration were consistent findings. Patients with abnormal leucocyte and/or platelet counts in the peripheral blood as well as patients with an excess of blast cells in the bone marrow had the lowest ALA-S activities. A further decrease in ALA-S activity was observed in 3 patients after leukaemic change in the disease. Patients having cytogenetic abnormalities showed no unique enzyme abnormalities. These results indicate that enzymatic disturbances of haem synthesis cannot be used as prognostic indicator of leukaemic transformation in refractory sideroblastic anaemia, but a very low ALA-S activity appears to accompany the development of a leukaemia in such patients.

The activities of delta-aminolaevulinic acid synthase and haem synthase in experimental sideroblastic anaemia. Effect of mitochondrial iron excess on the enzyme activity in peripheral red blood cells

Experimental sideroblastic anaemia was produced in normal and in iron loaded guinea pigs by intraperitoneal (i.p.) administration of isoniazid and cycloserine. Subsequently, the activities of delta-aminolaevulinic acid synthase (ALA-S) and of haem synthase in peripheral red blood cells were measured and in particular the relationships of enzyme activities to the iron status were examined. The ALA-S activity showed a similar decrease in all animals with sideroblastic anaemia. The haem synthase activity was increased probably due to secondary induction, but it was significantly less increased in animals with the highest values for iron status. This finding indicates that mitochondrial iron accumulation may have limited the compensatory increase of haem synthase activity. It is likely that also in human sideroblastic anaemia mitochondrial iron overload may have a secondary limiting effect on the haem synthase activity in erythroid cells.