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

[Diagnosis of the porphyrias : From A (as in aminolevulinic acid) to Z (as in zinc protoporphyrin)]

The porphyrias comprise a clinically, biochemically, and genetically heterogeneous group of predominantly hereditary metabolic disorders resulting from a dysfunction along the heme biosynthetic pathway. Whereas most variants can manifest with different cutaneous symptoms, some types only reveal life-threatening acute neurovisceral attacks. Therefore, interdisciplinary care of these patients is advisable. In this article, we provide an overview of characteristic clinical and laboratory findings in the various forms of porphyria and a diagnostic algorithm.

The genetic effects of environmental lead

This article reviews the effects of lead on genetic systems in the context of lead's various other toxic effects and its abundance and distribution in the environment. Lead is perhaps the longest used and best recognized toxic environmental chemical, yet it continued be used recklessly until only very recently. Lead is thus a lesson in the limitations and strengths of science, human conscience and common sense. Lead has been tested and found to be capable of eliciting a positive response in an extraordinarily wide range of biological and biochemical tests; among them tests for enzyme inhibition, fidelity of DNA synthesis, mutation, chromosome aberrations, cancer and birth defects. It reacts or complexes with many biomolecules and adversely affects the reproductive, nervous, gastrointestinal, immune, renal, cardiovascular, skeletal, muscular and hematopoietic systems as well as developmental processes. It is likely that lead is a selective agent that continues to act on and influence the genetic structure and future evolution of exposed plant and animal populations.

Studies of hybrid hematopoietic growth factor receptors

To gain further insight into the mechanisms by which both granulocyte-macrophage-colony stimulating factor (GM-CSF) and erythropoietin receptors function, we have utilized a GM-CSF erythropoietin hybrid receptor with GM-CSF as the external domain and erythropoietin as the intracellular domain. Results show that the beta common GM-CSF receptor both enhances the affinity binding of GM-CSF to the receptor and plays an important role in signaling through the receptor. A truncated form of the beta common receptor actually acts as a dominant negative regulatory factor.

Effect of alcohol on delta-aminolevulinic acid dehydratase and porphyrin metabolism in man

The influence of alcohol on porphyrin metabolism was investigated in 6 healthy non-alcoholics and 19 patients with chronic alcohol abuse. In the healthy subjects, blood and urine samples were obtained before and after acute alcohol exposure, whereas in the chronic alcoholics only one examination was performed. In both groups a significant inhibition of delta-aminolevulinic acid dehydratase was demonstrated. The activity was partially restored in vitro by addition of zinc ions or dithiothreitol. A combination of both activators produced reactivation to normal levels. Coproporphyrinuria was more prominent in chronic alcoholics (373 nmol/24 h on average, upper norm 119 nmol/24 h) compared to non-alcoholics (140 nmol/24 h). Urinary porphobilinogen and delta-amino-levulinic acid were normal except for a moderately increased delta-aminolevulinic acid in four healthy individuals. In conclusion, alcohol causes reversible inhibition of delta-aminolevulinic acid dehydratase. The metabolic changes reflect both an inhibition of delta-aminolevulinic acid dehydratase and coproporphyrinogen oxidase; a simultaneous, moderate induction of hepatic delta-aminolevulinic acid synthase is suggested. Erythrocyte delta-aminolevulinic acid dehydratase activity could serve as a sensitive indicator for both acute and chronic alcohol consumption even better than coproporphyrinuria.

delta-Aminolevulinic acid dehydratase isozymes and lead toxicity

ALAD is a zinc metalloenzyme whose inhibition by lead is the first and most sensitive indicator of lead exposure and whose decreased activity has been implicated in the pathogenesis of lead poisoning. This heme biosynthetic enzyme is encoded by a gene located at chromosome 9q34, which has two codominant alleles, ALAD1 and ALAD2. The occurrence of two frequent alleles for ALAD stimulated an investigation into the possible pharmacogenetic role of the enzyme polymorphism in lead poisoning. In a New York City population at high risk for lead exposure, individuals heterozygous or homozygous for the less common allele, ALAD2, had blood lead levels greater than or equal to 30 micrograms/dl more frequently than expected. These findings suggest a potential genetic susceptibility to lead poisoning in individuals with the ALAD 1-2 and 2-2 phenotypes.

Acute lead intoxication due to intravenous injection

A case of acute lead poisoning due to intravenous injection of lead acetate is reported. The patient developed clinical and biochemical symptoms characteristic for acute hepatic porphyrias. Elevated urinary 5-aminolaevulinic acid and low porphobilinogen correlated to a lead-induced inhibition of 5-amino-laevulinic acid dehydrase with diagnostically indicative reactivation rates by zinc and dithiothreitol. Urinary coproporphyrin excretion was also increased. Additional findings included anaemia and toxic hepatitis. Under the influence of elimination therapy with D-penicillamine pathologic parameters normalized. Except for transient neuralgic pains the patient did not experience any neurologic dysfunctions, thus contrasting the findings in chronic lead intoxication.

Lead poisoning as a toxogenetic disease

In two non-related patients suffering from acute lead intoxication a persistent decrease in red cell delta-aminolevulinic acid dehydratase (synonym: porphobilinogen synthase) activity of 30%-60% of controls was noted after treatment and normalisation of lead levels and heme precursors in urine and blood. An inherited enzyme deficiency was suggested and confirmed by a subnormal activity in the mothers of both patients. These four persons are considered as heterozygotes with an increased sensitivity to lead exposure.

Lead poisoning in inherited delta-aminolevulinic acid dehydratase deficiency

delta-Aminolevulinic acid dehydratase (ALA-D), respectively porphobilinogen synthase, EC 4.2.1.24) activity can be lowered by toxic, metabolic and hereditary factors. A 30-year-old painter was suffering from lead poisoning with an acute abdominal-neurologic syndrome and anemia. Blood lead was measured at 414 micrograms/l. Urinary ALA and coproporphyrin excretion as well as erythrocyte protoporphyrin had increased extremely, whereas ALA-D activity in erythrocytes had decreased extremely to 8% of controls. Excretion parameters, protoporphyrin, hemoglobin and lead returned to normal after treatment, but four years later ALA-D activity still remained diminished (30% of controls). An inherited enzyme deficiency was assumed and found in the mother, analogous to the subnormal ALA-D activity in heterozygotes of four other families. The inherited enzyme deficiency sensitized the patient to lead exposure and intoxication, which is a toxogenetic disease in this case.

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.

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.