Hereditary prophobilinogen synthase deficiency in human associated with acute hepatic porphyria

Deficiency of porphobilinogen synthase associated with acute crisis. Diagnosis of the first two cases in Chile by laboratory methods

Erythrocyte porphobilinogen synthase deficiency was confirmed by the determination of its activity in blood and also by the high levels of both porphyrins and 5-aminolaevulinic acid in the urine of two siblings. They presented with a picture of porphyric attack characterized by abdominal colic pain, high blood pressure, tachycardia and severe constipation. The profile of both porphyrins and their precursors in urine and blood resembled lead poisoning. However, this was ruled out because both patients had normal blood levels of lead. Furthermore, porphobilinogen synthase activity did not normalize when it was determined in the presence of dithiothreitol or dithiothreitol plus zinc chloride. No other causes to account for a deficiency in porphobilinogen synthase activity were identified. The simultaneous occurrence of similar clinical and biochemical symptoms suggests that the same triggering factor was present. Because the activity of porphobilinogen synthase was less than 4% of normal values, it is possible that these patients were homozygotes with respect to this defect, which could explain the presence of clinical symptoms. We propose that this metabolic defect is not uncommon and it should be kept in mind when diagnosing of porphyrias or heavy metal intoxications.

delta-Aminolevulinic acid dehydrase (porphobilinogen synthase) in two families with inherited enzyme deficiency

The inheritance of a deficient delta-aminolevulinic acid dehydrase (ALA-D; synonym: porphobilinogen synthase; EC 4.2.1.24) was studied in blood samples of two families over three generations. The propositus in each family was a young male acute hepatic porphyria patient with an almost complete ALA-D deficiency in the homozygous state (ALA-D activity less than 2% of controls). Heterozygotes are clinically non-affected (mean ALA-D 36% of controls). The mode of transmission could be traced by enzyme activity and electrophoretic polymorphism studies. Heterozygotes are detected by the demonstration of enzyme activity in the gel. The notation D was used for the gene expressing the defective enzyme. The "phenotype" D-1 was observed in six, the "phenotype" D-2 in three of all heterozygotes studied. These results are compatible with a single normal allele in heterozygotes responsible for enzyme activity. Quantitative assays and the segregation pattern in both families suggest a 3-allele-system for the inheritance of ALA-D deficiency.

Association of amino levulinate dehydratase levels and ferrochelatase inhibition in childhood lead exposure

The basis for the clinical variation in response to lead exposure in children is not well understood. We studied selected children from a large lead screening program in whom elevation of red cell protoporphyrin concentration (a measure of inhibition of the enzyme ferrochelatase) was markedly above or below average for a given blood lead level. We then measured the activity of the enzyme amino levulinate dehydratase in 306 of these children, and found that ALA-d activity was lower in children with higher protoporphyrin elevation, independent of the effects of lead. This observation, coupled with reports in the literature of families with ALA-d deficiencies and elevated red cell protoporphyrin values, makes likely a genetic basis for some of the variation in susceptibility to lead. The mechanism by which the two effects are associated remains unknown.

Hereditary hepatic porphyria with delta aminolevulinate dehydrase deficiency: immunologic characterization of the non-catalytic enzyme

Immunoreactive delta-aminolevulinate dehydrase (ALA-D) was measured in lysates from two porphyric patients with ALA-D deficiency (enzyme activities were below 2% of the normal level). By using two different immunologic methods, we found a cross-reactive immunologic material (CRIM+) which corresponded to 20% and 33% of the control level. Therefore the molecular basis that accounts for the deficiency of ALA-D in these patients is a structurally modified enzyme. The methods used to determine the molecular weight (by Western blotting) and the isoelectric point (by chromatofocusing) of the mutants did not show any difference by comparison with the normal enzyme.

Protoporphyrinogen oxidase and ferrochelatase in porphyria variegata

Protoporphyrinogen oxidase activity and ferrochelatase activity were measured in leucocytes from patients with porphyria variegata. The mean activity of protoporphyrinogen oxidase (PPO) in porphyria variegata (PV) was about 50% of normal (P less than 0.05). The mean activity of ferrochelatase with 59Fe2+ sulphate and protoporphyrin as substrates (in the presence of ascorbic acid) was reduced by 40% (P less than 0.009). The mean activity of ferrochelatase with 59Fe3+ chloride and protoporphyrin as substrates (in the presence of reduced glutathione) was increased by 65% (P less than 0.005). Both are statistically highly significant. The findings are interpreted as follows: (a) The occurrence of a low level of protoporphyrinogen oxidase in PV is confirmed. (b) The findings indicate a concurrent structural change in ferrochelatase (this may be structurally related to (a) but no evidence of this is at present available).

Porphobilinogen-synthase (delta-aminolevulinic acid dehydratase) deficiency in bone marrow cells of two patients with porphobilinogen-synthase defect acute porphyria

Two male patients aged 23 and 25 years with intermittent acute, frequently repeated porphyria syndromes presented an almost total deficiency of porphobilinogen-synthase [(PBG-S); synonym: delta-aminolevulinic acid dehydratase] in peripheral erythrocytes. PBG-S was investigated in bone marrow cells obtained by sternal puncture. A minimal enzyme activity of less than 3% of controls was established. Specific activity and protoporphyrin concentration decreased considerably during the course of erythropoiesis. Both patients are homozygous gene carriers; their parents (father and mother) as well as most of their brothers and sisters are heterozygotes with a PBG-S deficiency of approximately 50% of controls. All people with PBG-S deficiency are especially endangered by alcohol intake and lead exposure, because alcohol and lead toxically inhibit PBG-S.

Acute lead poisoning in inherited porphobilinogen synthase (delta-aminolevulinic acid dehydrase) deficiency

The second enzyme of the porphyrin and heme synthesis pathway, porphobilinogen synthase (EC 4.2.1.24), can be lowered due to a hereditary defect or toxic damage. Lead is the most common cause for a toxically lowered activity. We report on a 48-year-old patient with an acute abdominal syndrome, anemia and a grave toxic disorder of porphyrin metabolism which was diagnosed as acute lead intoxication. Although the hematologic findings and porphyrins in the blood, as well as porphyrin precursors and porphyrin excretion in the urine, returned to normal within five months after exacerbation of the acute symptoms the activity of porphobilinogen synthase showed only 50% physiologic activity of healthy subjects six years after the acute syndrome with complete normalization of prophyrin metabolites and lead levels in blood and urine. The influence of alcohol was excluded. Enzyme activation by zinc and reactivation by dithiothreitol lies within the normal range and thus contradicts an increased body burden of lead. In connection with findings of a familiar porphobilinogen synthase defect we are most likely dealing with a hereditarily determined enzyme deficiency in this patient which sensitizes him to a lead intoxication.

Persistent protoporphyrinemia in hereditary porphobilinogen synthase (delta-aminolevulinic acid dehydrase) deficiency under low lead exposure. A new molecular basis for the pathogenesis of lead intoxication

For several years, a 4-12-fold increase of the upper normal limit in erythrocyte protoporphyrin concentrations persisted in two men 34 and 39 years of age who were chronically exposed to lead. We are dealing with a zinc protoporphyrinemia in both cases, without lead intoxication or anemia. The 34-year-old had been a regular blood donor for 10 years and had already been treated for iron deficiency several times. Hemoglobin, red cell counts, hematocrit, and iron were at the lower normal limit. The activity of porphobilinogen synthase (PBG-S), uroporphyrinogen-synthase and -decarboxylase as well as urinary porphyrin precursors and porphyrin excretion were normal. Protoporphyrinemia was said to be due to a prelatent/latent iron deficiency. In the 39-year-old, the activity of PBG-S was lowered to 388 mumol/1 . h, as compared to the mean of controls (1,190 +/- 210, x +/- SD, n = 50), in connection with a slightly elevated excretion of delta-aminolevulinic acid and coproporphyrin in the urine and a high-normal blood lead level. In his family there was no history of either a protoporphyrinemia or a hematological disturbance. Six of eight family members in three generations showed a diminished activity of PBG-S: 600 +/- 160, P less than 0.001 compared to controls. These family members are heterozygous with regard to the PBG-S deficiency; they are clinically unobtrusive in comparison to homozygotes with an acute prophyria syndrome. Activation by zinc and reactivation by dithiothreitol were normal in contrast to PBG-S from patients with lead intoxication. The cause of biochemical symptoms of subclinical lead intoxication developed by the propositus is probably due to the hereditary PBG-S deficiency which sensitizes him to low-level lead exposure. The determination of red cell PBG-S activity can be recommended as a test detecting heterozygotes. The hereditary PBG-S deficiency is recognized as a new molecular basis for the pathogenesis of lead intoxication.

New type of acute porphyria with porphobilinogen synthase (delta-aminolevulinic acid dehydratase) defect in the homozygous state

In two male patients with acute hepatic porphyria and persisting paralysis which increased in intensity intermittently, the activity of porphobilinogen synthase (PBG-S; delta-aminolevulinic acid dehydr(at)ase) was diminished in peripheral erythrocytes and bone marrow cells below 3% of normal controls. In contrast, the activities of uroporphyrinogen synthase and decarboxylase were normal. Both patients have been excreting high quantities of delta-aminolevulinic acid and porphyrins in urine for years. Lead intoxication and tyrosinemia could definitely be excluded. There was no experimental evidence for the existence of an inhibitor to PBG-S in urine, serum and erythrocytes from these two patients. The PBG-S deficiency was confirmed after DEAE cellulose chromatography: the concordance of relative and specific activity before and after chromatography of PBG-S from patients and controls differs from the findings in lead poisoning. A mutation of PBG-S probably at the level of the structural gene is concluded as the molecular basis of the inherited PBG-S defect porphyria. Since the relatives also show lower activities of PBG-S (approximately 50% of controls), the disease of these two patients represents a new enzymatic type of inherited acute hepatic porphyria, the excretion profile of which is qualitatively completely different from those of the known acute porphyrias. The discovery of this porphyria confirms the theory of overlapping transition in the biochemical signs and clinical symptoms as well as analogies among the acute hepatic porphyrias and lead poisoning.