Severe homocysteinemia in two givosiran-treated porphyria patients: is free heme deficiency the culprit?

Givosiran is a novel approach to treat patients with acute intermittent porphyrias (AIP) by silencing of ∂-ALA-synthase 1, the first enzyme of heme biosynthesis in the liver. We included two patients in the Envision study who responded clinically well to this treatment. However, in both patients, therapy had to be discontinued because of severe adverse effects: One patient (A) developed local injection reactions which continued to spread all over her body with increasing number of injections and eventually caused a severe systemic allergic reaction. Patient B was hospitalized because of a fulminant pancreatitis. Searching for possible causes, we also measured the patients plasma homocysteine (Hcy) levels in fluoride-containing collection tubes: by LC-MS/MS unexpectedly, plasma Hcy levels were 100 and 200 in patient A and between 100 and 400 μmol/l in patient B. Searching for germline mutations in 10 genes that are relevant for homocysteine metabolism only revealed hetero- and homozygous polymorphisms in the MTHFR gene. Alternatively, an acquired inhibition of cystathionine-beta-synthase which is important for homocysteine metabolism could explain the plasma homocysteine increase. This enzyme is heme-dependent: when we gave heme arginate to our patients, Hcy levels rapidly dropped. Hence, we conclude that inhibition of ∂-ALA-synthase 1 by givosiran causes a drop of free heme in the hepatocyte and therefore the excessive increase of plasma homocysteine. Hyperhomocysteinemia may contribute to the adverse effects seen in givosiran-treated patients which may be due to protein-N-homocysteinylation.

Dysregulation of homocysteine homeostasis in acute intermittent porphyria patients receiving heme arginate or givosiran

Acute intermittent porphyria (AIP) is a rare metabolic disease caused by mutations within the hydroxymethylbilane synthase gene. Previous studies have reported increased levels of plasma total homocysteine (tHcy) in symptomatic AIP patients. In this study, we present long-term data for tHcy and related parameters for an AIP patient cohort (n = 37) in different clinical disease-states. In total, 25 patients (68%) presented with hyperhomocysteinemia (HHcy; tHcy > 15 μmol/L) during the observation period. HHcy was more frequent in AIP patients with recurrent disease receiving heme arginate, than in nonrecurrent (median tHcy: 21.6 μmol/L; range: 10-129 vs median tHcy: 14.5 μmol/L; range 6-77). Long-term serial analyses showed a high within-person tHcy variation, especially among the recurrent patients (coefficient of variation: 16.4%-78.8%). HHcy was frequently associated with low blood concentrations of pyridoxal-5'-phosphate and folate, while cobalamin concentration and the allele distribution of the methylene-tetrahydrofolate-reductase gene were normal. Strikingly, 6 out of the 9 recurrent patients who were later included in a regime of givosiran, a small-interfering RNA that effectively reduced recurrent attacks, showed further increased tHcy (median tHcy in 9 patients: 105 μmol/L; range 16-212). Screening of amino acids in plasma by liquid-chromatography showed co-increased levels of methionine (median 71 μmol/L; range 23-616; normal <40), suggestive of acquired deficiency of cystathionine-β-synthase. The kynunerine/tryptophan ratio in plasma was, however, normal, indicating a regular metabolism of tryptophan by heme-dependent enzymes. In conclusion, even if HHcy was observed in AIP patients receiving heme arginate, givosiran induced an aggravation of the dysregulation, causing a co-increase of tHcy and methionine resembling classic homocystinuria.

Haem Biosynthesis and Antioxidant Enzymes in Circulating Cells of Acute Intermittent Porphyria Patients

The aims of the present study were to explore the expression pattern of haem biosynthesis enzymes in circulating cells of patients affected by two types of porphyria (acute intermittent, AIP, and variegate porphyria, VP), together with the antioxidant enzyme pattern in AIP in order to identify a possible situation of oxidative stress. Sixteen and twelve patients affected by AIP and VP, respectively, were analysed with the same numbers of healthy matched controls. Erythrocytes, neutrophils and peripheral blood mononuclear cells (PBMCs) were purified from blood, and RNA and proteins were extracted for quantitative real time PCR (qRT-PCR) and Western-blot analysis, respectively. Porhobilinogen deaminase (PBGD) and protoporphyrinogen oxidase (PPOX) gene and protein expression was analysed. Antioxidant enzyme activity and gene expression were additionally determined in blood cells, together with protein carbonyl content in plasma. PBMCs isolated from AIP patients presented low mRNA levels of PBGD when compared to controls, while PBMCs isolated from VP patients presented a decrease in PPOX mRNA. PPOX protein content was higher in AIP patients and lower in VP patients, compared to healthy controls. Regarding antioxidant enzymes, PBMCs and erythrocyte superoxide dismutase (SOD) presented statistically significant higher activity in AIP patients compared to controls, while catalase activity tended to be lower in these patients. No differences were observed regarding antioxidant gene expression in white blood cells. Circulating cells in AIP and VP patients present altered expression of haem biosynthetic enzymes, which could be useful for the differential diagnosis of these two types of porphyria in certain difficult cases. AIP patients present a condition of potential oxidative stress similar to VP patients, evidenced by the post-transcriptional activation of SOD and possible catalase impairment.

[A family of acute intermittent porphyria]

A 62-year-old man who had twice received laparotomies for abdominal pain of unknown origin was admitted to our hospital with acute abdominal pain. His family history of acute intermittent porphyria (AIP) suggested that it arose from acute porphyria. We treated the patient with 5% glucose solution by i.v. drip infusion and his abdominal pain improved rapidly. Diagnosis of AIP was established by the demonstration of reduced erythrocyte porphobilinogen deaminase (PBGD) activity and a point mutation (CAG --> CGG) in a splicing site in intron 10/exon 11 in the PBGD gene by DNA analysis. For screening of AIP carriers in his family, we measured erythrocyte PBGD activity. Four of his seven children were successfully diagnosed as AIP carriers. This is the ninth AIP family report, in which a mutation in the PBGD gene was revealed by DNA analysis.

Homozygous acute intermittent porphyria in a 7-year-old boy with massive excretions of porphyrins and porphyrin precursors

A 7-year-old boy demonstrating hepatosplenomegaly, mild anaemia, mild mental retardation, yellow-brown teeth and dark red urine had excessively elevated levels of urinary delta-aminolevulinic acid, porphobilinogen and uroporphyrin. Furthermore hepta-, hexa-, penta- and copro(I)porphyrins were highly increased in urine. This pattern of porphyrin precursor and metabolite excretion is characteristic of acute intermittent porphyria. The decreased copro(III)/copro(I+III) ratio, normally not found in acute intermittent porphyria, is discussed. The porphobilinogen deaminase activity in red cells was decreased to 2-4%. Mutation analysis revealed a novel homozygous L81P mutation in exon 6 of the porphobilinogen deaminase gene. The father and mother, shown to be gene carriers of the same mutation, are asymptomatic and have normal urinary porphyrin precursor and metabolite excretion.

Molecular and biochemical studies of acute intermittent porphyria in 196 patients and their families

BACKGROUND

Acute intermittent porphyria (AIP) is a metabolic disease with clinical manifestations that mimic other abdominal, neurologic, or mental crises. We studied the diagnostic accuracy of current laboratory tests during an acute attack and in remission.

METHODS

Since 1966, we have studied all known Finnish AIP patients (n = 196) and their families (n = 45) and identified the porphobilinogen deaminase (PBGD) mutation in each family. Diagnoses or exclusions of AIP were based on clinical data (including family history), biochemical tests, and in 239 cases, mutation testing. We retrospectively evaluated the diagnostic accuracy of erythrocyte PBGD activity, urinary excretion of porphobilinogen (PBG) and delta-aminolevulinic acid, and urinary and fecal excretion of porphyrins in these patients.

RESULTS

Measurement of urinary PBG identified all 35 AIP patients studied during an acute attack. The mean excretion of PBG was 50-fold above the reference interval, although the intraindividual increases were modest (1.6- to 4.0-fold). In the mutation-screened population, urinary PBG analysis identified only 85% of 81 AIP patients studied during remission, but by ROC curve analysis it was nonetheless the best of the biochemical tests. It was increased <or=2-fold in 29% of healthy relatives. Erythrocyte PBGD activity was decreased in only 84% of AIP patients, with results within the reference interval mainly in the variant form of AIP; it was decreased in 23% of healthy relatives.

CONCLUSIONS

Measurement of urinary PBG is the best biochemical test for AIP, although it is unspecific and does not distinguish AIP from other acute porphyrias. Because the acute increase in PBG is often modest, the medical history, signs, and symptoms must be evaluated carefully during an acute attack. In addition, because biochemical analyses often remain indeterminate in remission, mutation analysis is needed to exclude or confirm the diagnosis of AIP.

Acute intermittent porphyria in Sweden. Molecular, functional and clinical consequences of some new mutations found in the porphobilinogen deaminase gene

Acute intermittent porphyria (AIP) is an autosomal dominant disorder caused by a partial deficit of porphobilinogen deaminase (PBGD), the third of eight enzymes in the haem biosynthetic pathway. The overt disease is characterized by neuropsychiatric symptoms that are often triggered by exogenous factors such as certain drugs, stress, and alcohol. The aim of this work has been to identify the underlying genetic defect in each AIP-affected family in order to provide early counselling to assist in the avoidance of precipitating factors. The prevalence of AIP in Sweden is in the order of 1:10 000. The major mutation in Sweden, W198X, is due to a founder effect in the northern part of the country. This mutation, together with a further 11 mutations, have been reported previously. The present communication encompasses the great majority of AIP kindreds in Sweden and includes a further 27 mutations within the PBGD gene. This includes 14 completely new mutations, as well as 11 known mutations detected for the first time in Sweden. The majority of the mutations are located in exons 10 and 12 with fewer in exon 7. The clinical and biochemical outcomes in some patients are described. We also use the three-dimensional structure of the porphobilinogen deaminase enzyme to predict the possible molecular and functional consequences of the new Swedish missense and nonsense mutations.

Reliability of PCR-based detection of occult tumour cells: lessons from real-time RT-PCR

For the molecular detection of rare tumour cells in clinical samples, real-time reverse transcription-polymerase chain reaction (RT-PCR) offers two important advantages over conventional RT-PCR assays: the results are quantitative and, perhaps more importantly, it facilitates exact sensitivity controls on a per sample basis as well as exact comparison of different assay protocols. We report here on quantitative results obtained with different protocols for RNA isolation and cDNA synthesis for amplification of beta2-microglobulin transcripts using the light cycler system. Furthermore, housekeeping gene-specific PCRs were compared with PCRs specific for an artificial transcript (internal standard) detected simultaneously at a level comparable to the wild-type sequence. Artificial tyrosinase transcripts derived from a vector construct stably transfected into a human lymphoma cell line were used as a model to test the usefulness of artificial internal standards as an alternative to housekeeping genes. The highest RNA yields were obtained using a combination of phenol-chloroform extraction and the High Pure RNA Isolation Kit. Analysing beta2-microglobulin transcript-specific RT-PCRs, the highest sensitivity was obtained for cDNAs generated with Omniscript reverse transcriptase and oligo-p(dT)15 primer. Regarding patient blood samples, RT-PCRs specific for beta2-microglobulin, porphobilinogen deaminase and artificial tyrosinase transcripts provided quantitative data for all, for 18 out of 21, and for 10 out of 21 samples, respectively. Quantification of beta2-microglobulin transcripts by the light cycler system defined the protocol revealing the highest cDNA quality. Comparisons of quantitative data from RT-PCRs specific for beta2-microglobulin, porphobilinogen deaminase and artificial tyrosinase transcripts enabled us to determine a close range for crossing points within which sufficient cDNA quality can be guaranteed, even for the detection of rare transcripts. PCRs specific for the artificial internal standard are ideally suited for cDNA quality assessment on a per sample basis.

Determination of porphobilinogen deaminase activity in human erythrocytes: pertinent factors in obtaining optimal conditions for measurements

Determination of porphobilinogen deaminase (PBGD; EC 4.3.1.8) activity in erythrocytes can contribute to the identification of patients suspected of acute intermittent porphyria. PBGD catalyses the polymerization of four molecules of porphobilinogen (PBG) to the highly unstable 1-hydroxymethylbilane. The 1-hydroxymethylbilane is transformed into uroporphyrinogen III by uroporphyrinogen III synthase. When this enzyme is inactivated, 1-hydroxymethylbilane cyclizes non-enzymatically to uroporphyrinogen I, which can be oxidized to uroporphyrin I. PBGD activity can be measured by quantitation of uroporphyrin I formed from PBG under conditions where this is the only end product. The purpose of the present study was to define the optimal conditions for quantitating PBGD activity in human erythrocytes. The preanalytical factors examined were: anticoagulants and methods for disruption of the erythrocytes. The analytical factors examined were: duration of preincubation, reaction time, reaction temperature, pH, ionic strength and conditions for the oxidation of uroporphyrinogen I to uroporphyrin I. Based on the results, we propose an optimized method for determination of PBGD activity in erythrocytes.

Prevalence of acute intermittent porphyria in a Mexican psychiatric population

BACKGROUND

Acute intermittent porphyria is a hereditary error of porphyrin metabolism in which the main metabolic defect is caused by a decrease in porphobilinogen deaminase activity. Previous work has demonstrated a higher prevalence of acute intermittent porphyria in the psychiatric patient population than in the general population. The goal of this study was evaluate 300 psychiatric patients and 150 control subjects to detect acute intermittent porphyria by measurement of porphobilinogen (PBG) deaminase activity in blood.

METHODS

Screening for porphobilinogen deaminase activity was carried out by fluorometric measurement of porphyrins synthesized during 1 h in blood and the measurement of delta-aminolevulinic acid and porphobilinogen in urine.

RESULTS

We found two psychiatric patients, one male and one female, with decreased porphobilinogen deaminase activity. When the families of these patients were studied, one brother was found to have an abnormality. Among controls, a woman was found to have the abnormality and her father was found to have typical features of the disease.

CONCLUSIONS

These results indicate a prevalence of porphyria in Mexican psychiatric patients similar to controls, and that measurement of PBG deaminase activity is a good tool for defining acute intermittent porphyria carriers.

Reference values of 5-aminolevulinate dehydrase and porphobilinogen deaminase in the Spanish population from Madrid

5-Aminolevulinate dehydrase (ALA-D) and porphobilinogen deaminase (PBG-D) are cytosolic enzymes involved in heme biosynthesis. ALA-D activity is altered both genetically and by the action of various environmental factors, including exposure to lead. The activity of PBG-D is reduced in acute intermittent porphyria. The aim of this work is to establish the 95% reference range of the erythrocytic activity of ALA-D and PBG-D in a control population. ALA-D activity limits were 15.8 and 50.2 nmol of PBG/ml of red blood cells (RBCS) per minute. For the activity of ALA-D restored by addition of zinc and dithiothreitol ("restored ALA-D"), these limits were 44.1 and 86.5 units. It has been found that the "restored ALA-D"/ALA-D ratio is very useful for the evaluation of lead toxicity, and its 95% reference range was between 1.22 and 3.06. It has been demonstrated that the best method for measuring erythrocytic PBG-D is using PBG, but not ALA, as substrate; its 95% reference range was between 20.9 and 63.2 nmol of uroporphyrin/ml of RBCs per hour. Knowledge of these reference range values in a control population constitutes the basis for an accurate diagnosis of heavy metal intoxication and acute intermittent porphyria.

Lead induced disorders in hematopoietic and drug metabolizing enzyme system and their protection by ascorbic acid supplementation

Effect of vitamin C supplementation in restoring lead induced alterations in hematopoietic system and drug metabolizing enzymes were investigated in male rats. Intraperitoneal administration of 20 mg/kg lead produced a significant inhibition of heme synthesis in blood and liver and drug metabolism in liver. Toxic insult by lead also resulted into a marked decline in tissue thiols and vitamin C levels. Oral supplementation of vitamin C (100 mg/kg for 3 days) completely restored blood delta aminolevulinic acid dehydratase, uroporphyrinogen I synthetase and a few drug metabolizing enzymes. Level of vitamin C and sulfhydryl contents too recovered to a great extent. A marked reduction in blood and liver lead concentration occurred on vitamin C supplementation although renal lead contents were marginally reduced in lead exposed animals. The results, thus, indicate a significant protective action of vitamin C against toxic effects of lead on heme synthesis and drug metabolism.

Acute intermittent porphyria: prevalence of mutations in the porphobilinogen deaminase gene in blood donors in France

OBJECTIVES

Acute intermittent porphyria (AIP) is an autosomal dominant disorder resulting from a 50% deficiency in porphobilinogen deaminase (PBG deaminase). The true prevalence in the general population of mutations in the PBG deaminase gene capable of causing AIP is unknown. However, it is important to identify asymptomatic carriers of AIP mutations because all are at risk to have an acute attack.

DESIGN

We measured erythrocyte PBG deaminase from 3350 healthy blood donors. When a clear cut deficiency (< mean minus 2.5 SD) was found, the PBG deaminase gene was analysed by molecular biology technics.

SUBJECTS

Four subjects with PBG deaminase deficiency were identified. Two had mutations in the PBG deaminase gene which are known to cause AIP.

CONCLUSION

We conclude that, in France, the mutations of the PBG deaminase gene show a high prevalence in the healthy population. If only these two confirmed latent cases are used for the calculation, in France the minimal prevalence of the AIP gene is 1:1675.

Molecular epidemiology and diagnosis of PBG deaminase gene defects in acute intermittent porphyria

Acute intermittent porphyria (AIP) is the major autosomal dominant form of acute hepatic porphyrias. The disease is due to mutations in the gene encoding for porphobilinogen (PBG) deaminase and is characterized by life-threatening neurovisceral attacks, often precipitated by drugs, fasting, cyclical hormonal changes, or infectious diseases. This report describes a prospective study on the molecular epidemiology of PBG deaminase gene defects in AIP. It uses a sensitive, reliable, and easy-to-handle method for routine AIP molecular diagnosis and family study based on an exon-by-exon denaturing gradient gel electrophoresis (DGGE) strategy followed by direct sequencing. Fifteen genomic DNA fragments, including all the coding sequence and covering 3.35 kb of the PBG deaminase gene, were investigated in 405 subjects from 121 unrelated French Caucasian AIP families who had not been screened previously at the DNA level. PBG deaminase gene mutations were identified in 109 families, but only 78 were of different type, and each of them had a prevalence rate < 5%. Among these mutations, 33 had not been published previously. Sixty percent of these 78 mutations were located in only three exons (exons 10, 12, and 14), 44% were missense, 18% were splice defect, 19% were frameshift, and 16% were nonsense. In addition, two de novo mutational events were characterized. The evaluation of the efficiency of the standard PBG deaminase enzymatic screening method for gene-carrier detection indicated 95% of concordancy with the molecular-based diagnosis.

Molecular analysis of porphobilinogen (PBG) deaminase gene mutations in acute intermittent porphyria: first study in patients of Slavic origin

Acute intermittent porphyria (AIP) is an autosomally dominant inherited metabolic disorders caused by decreased activity of porphobilinogen deaminase, the third enzyme in the human heme biosynthetic pathway. We report here the first mutations in the human porphobilinogen deaminase gene in seven unrelated patients from the Czech and Slovak Republics with acute intermittent porphyria. We used denaturing gradient gel electrophoresis to screen all 15 exons and exon/intron boundaries of the porphobilinogen deaminase gene. Polymerase chain reaction products of abnormal migration patterns were subjected to direct sequencing to identify the causative mutations. Thus we revealed four novel mutations and three which have been previously described. Of the four novel mutations, two were mis-sense (G24S, V267M), one was a single base insertion (158insA) that produced a stop codon 12 codons downstream, and one was a single base substitution in intron 12 (771 + 1) resulting in a splicing defect. The three previously detected mutations were mis-sense mutations (R26C, R26H, G111R). These results suggest a high allelic heterogeneity in Czech and Slovak patients.

Effect of beryllium chloride on porphyrin metabolism in pregnant mice administered by subcutaneous injection

The effect of beryllium (Be) compounds on porphyrins was investigated in pregnant mice. The blood protoporphyrin (Proto) and zinc protoporphyrin (Zn Proto) concentrations were increased in pregnancy. Regardless of pregnancy or nonpregnancy, the Proto concentration was decreased after Be injection. Delta-aminolevulinic acid dehydratase (ALA-D) and porphobilinogen deaminase (PBG-D) activities in blood were significantly elevated in the pregnant untreated (Con-pregnant) group, compared to the nonpregnant mice untreated (Con-nonpregnant) and nonpregnant mice treated with Be (Be-nonpregnant) groups. The blood ALA-D activity of the pregnant mice treated with Be (Be-pregnant group) tended to decrease, compared to Con-pregnant group. The blood PBG-D activity in the Be-pregnant group was significantly lower compared with that of the Con-pregnant group. The ALA-D and PBG-D activities in the spleen were also significantly elevated in the Con-pregnant group, compared to nonpregnant groups. However, it was noted that these values in the Be-pregnant group were almost the same as that of the Con-nonpregnant group and were significantly lower than that in the Con-pregnant group. The elevation of ALA-D and PBG-D activities in the blood and spleen, which play a role in the hematopoietic function of mice, was observed in the Con-pregnant mice compared to the nonpregnant mice. However, the phenomenon was not observed in the Be-pregnant mice, it suggesting that Be suppressed the pregnancy-induced increase in hematopoietic function.

Interdependence between degree of porphyrin excess and disease severity in congenital erythropoietic porphyria (Günther's disease)

Various clinical and biochemical observations point to a relationship between degree of disease expression and metabolic disturbance in autosomal recessive congenital erythropoietic porphyria (Günther's disease). Although the clinical manifestations have been well described since Günther's fundamental observations, an interdependence between disease severity and porphyrin excess has yet to be elucidated. We investigated porphyrin metabolism in nine Indian patients suffering from the characteristic clinical symptoms: skin photosensitivity, red-colored urine as a sign of extremely elevated porphyrinuria and mild to severe hemolytic anemia. Porphyrins in urine, feces and blood were analysed by HPTLC and HPLC in conjunction with spectrophotometry and spectrofluorometry. Uroporphyrinogen III synthase activities in red blood cells were determined using a coupled-enzyme assay. Biochemical studies revealed varying degrees of porphyrinuria with total urinary porphyrins between 23 and 102 mumol/24 h (normal < 0.2 mumol/24 h) and uroporphyrin predominance. Urinary and fecal coproporphyrin isomer I were markedly elevated to 87-97% and 81-93% (normal < 31%, < 75%), respectively. Overproduction of porphyrins led to a considerable porphyrinemia with mainly copro- and protoporphyrin. A hitherto undescribed fecal porphyrin pattern with increased protoporphyrin levels was found in three patients. This atypical finding was probably related to severe hemolysis since protoporphyrin can be excreted only via the liver with bile in the feces. High porphyrin levels in urine, feces and blood were associated with worse cutaneous symptoms. Activities of uroporphyrinogen III synthase in red blood cell lysates were decreased to between 9% and 30% of controls. Patients showed increased porphobilinogen deaminase activities, up to 190% of control. Deficiency of uroporphyrinogen III synthase activity was reflected by inversion of the relationship between and isomer III leading to dominance of isomer I. Elevation of porphobilinogen deaminase activities is related to hemolysis and, additionally, to regulatory compensation for the enzyme deficiency. Variations in both the severity of photosensitivity and the enhancement of porphyrin production and excretion indicate the molecular heterogeneity of this disease. These findings suggest a close relationship between the metabolic disturbance reflected by porphyrin excess and the severity of disease expression.

Heterogeneity of acute intermittent porphyria: a subtype with normal erythrocyte porphobilinogen deaminase activity in Germany

Patients with acute intermittent porphyria can be subdivided into three groups, according to the porphobilinogen deaminase activity in their erythrocytes. The first group has lowered, the second overlapping and the third normal porphobilinogen deaminase activity. Of 385 acute intermittent porphyria patients 5% had normal porphobilinogen deaminase activity. Gene carriers of acute intermittent porphyria, which have normal porphobilinogen deaminase activity but display slight, moderate or high aberrations of excretion, are recognized by analysis of urinary haem precursors and faecal porphyrins. Six individuals suffering from acute intermittent porphyria were detected in three families with normal porphobilinogen deaminase. There were no differences in the latent and clinical phases of acute intermittent porphyria between patients with lowered and those with normal porphobilinogen deaminase. One female with normal activity in erythrocytes, in which the porphyria disease process is triggered by barbiturates and carbamazepine, is presented. After therapy with high doses of glucose and omission of inducing agents, this woman was free of symptoms, and the excretion of different urinary porphyrin precursors and porphyrins decreased by between 65 and 93%.

Effects of recombinant human erythropoietin on porphyrin metabolism in uremic patients on hemodialysis

Recombinant human erythropoietin (r-HuEPO) is being successfully used for the treatment of uremic anemia. Several abnormalities of heme biosynthetic pathway have been described in patients with end-stage renal failure. In this condition, the activity of erythrocyte porphobilinogen deaminase has been found to be slightly increased. If this enzyme were to be the key enzyme in erythroid heme regulation, its activity would be increased to an even greater degree during the correction of uremic anemia. To assess this hypothesis, this study followed the variations of this and other parameters of porphyrin metabolism over 12 months of erythropoietin therapy in eight patients with nephrogenic anemia who underwent hemodialysis. By the first month of therapy, an increase of the previously depressed erythrocyte activity of aminolevulinate dehydratase was already evident, in coincidence with a nonsignificant increase of the reticulocyte count. The activity of this enzyme reached its maximal level by Month 3, and did not change up to Month 10. The porphobilinogen deaminase hyperactivity normalized at Month 4. By Month 12, in coincidence with the reduction of erythropoietin doses, the maximal levels of erythrocyte protoporphyrin, and the decrease in aminolevulinate dehydratase activity, the porphobilinogen deaminase values started to increase once again. In conclusion, the administration of r-HuEPO to hemodialyzed patients induced transient normalization of the previously observed porphyrin metabolism abnormalities. However, erythrocyte porphobilinogen deaminase activity did not rise concomitantly with the increase in hematocrit or hemoglobin values, but it did diminish during treatment. Therefore, porphobilinogen deaminase did not behave as a controlling enzyme in heme synthesis during the r-HuEPO-induced correction of uremic anemia.

Altered 5-aminolevulinic acid metabolism leading to pseudoporphyria in hemodialysed patients

Hemodialysed patients with no history of porphyria may present neurological symptoms similar to those seen in acute porphyrias. Porphyria has been associated with an increase in plasma levels of 5-aminolevulinic acid and porphobilinogen. Our aim was to evaluate these parameters and the activities of the enzymes involved in the first steps of heme metabolism in non-porphyric hemodialysed patients. The activities of 5-aminolevulinate dehydratase and deaminase were determined in red blood cells (RBC) from 78 hemodialysed patients, before and after dialysis. Plasma levels of 5-aminolevulinic acid, porphobilinogen and zinc were also measured. These parameters were also measured in 40 volunteers to obtain controls levels. The levels of 5-aminolevulinic acid (0.98 +/- 0.09 microgram/ml) and porphobilinogen (1.32 +/- 0.13 micrograms/ml) were raised in non-porphyric patients prior to hemodialysis (P < 0.001) compared with controls (5-aminolevulinic acid 0.13 +/- 0.02 microgram/ml; porphobilinogen 0.90 +/- 0.09 microgram/ml). After dialysis there was a decrease in both 5-aminolevulinic acid (to 0.61 +/- 0.05 microgram/ml) and porphobilinogen (to 1.10 +/- 0.16 micrograms/ml) although both parameters remained higher than controls (P < 0.001). The activities of both 5-aminolevulinate dehydratase (0.550 +/- 0.095 U/ml RBC), and deaminase (54.13 +/- 9.13 U/ml RBC) were diminished in blood samples of patients before dialysis (P < 0.001) compared to controls (dehydratase 0.975 +/- 0.115 U/ml RBC; deaminase 77.32 +/- 10.00 U/ml RBC). After dialysis 5-aminolevulinate dehydratase activity was partially recovered (to 0.666 +/- 0.100 U/ml RBC) while deaminase returned to normal values (73.45 +/- 9.46 U/ml RBC). The plasma zinc concentration in hemodialysed patients (44 +/- 12 micrograms/100 ml) was significantly lower than controls (105 +/- 30 micrograms/100 ml, P < 0.001). Addition of 22.5 mM zinc to the dehydratase reaction mixture raised the activity of 5-aminolevulinate dehydratase in blood samples of hemodialysed patients taken before and after dialysis. The study reports a partial loss of activity of 5-aminolevulinate dehydratase and deaminase activities in red blood cells from non-porphyric patients undergoing hemodialysis. Since plasma zinc levels were below normal in hemodialysed patients, and the activity of 5-aminolevulinate dehydratase could be restored by the addition of zinc, it is suggested that these abnormalities in heme metabolism may be explained by altered zinc and associated antioxidant status following dialysis.

[Porphyrin-synthesizing enzymes in erythrocyte]

There are 4 different porphyrin-synthesizing enzymes, i.e. delta-aminolevulinic acid dehydratase, porphobilinogen deaminase, uroporphyrinogen III synthase and uroporphyrinogen decarboxylase, in red blood cells. Determination of activities of these enzymes is of great help in clarifying the hemopoietic mechanism operating in bone marrow erythroblasts, as well as, in establishing the diagnosis of or early detection of acute intermittent porphyria, congenital erythropoietic porphyria, delta-aminolevulinic acid dehydratase deficiency porphyria, porphyria cutanea tarda and lead poisoning. This paper presents a summary of the techniques for the measuring, diagnostic criteria for and clinical implications of activities of these 4 enzymes in red blood cells.

Relation between uroporphyrin excretion, acute attacks of hereditary coproporphyria and successful treatment with haem arginate

1. The increased urinary excretion of porphyrins as well as of their precursors was studied in a patient with hereditary coproporphyria during two acute attacks in which symptoms differed markedly in character and severity. 2. The increase in urinary coproporphyrin was similar in the 'mild' and in the 'severe' attack, indicating a lack of correlation between coproporphyrin level and clinical symptoms. 3. Aminolaevulinic acid, porphobilinogen and uroporphyrin exhibited significantly higher values during the 'severe' attack than during the 'mild' attack. During the severe attack these three compounds were increased 18-, 14- and 46-fold, respectively, compared with increases of 3-, 3- and 8-fold, respectively, during the mild attack. 4. The striking rise in the formation of uroporphyrin was reflected in the plasma porphyrin profile, which revealed predominance of uroporphyrin. In accordance with this finding, an increase in erythrocyte porphobilinogen deaminase of 130% was recorded. 5. The fluorescence emission spectra of saline-diluted plasma (excitation of 405 nm) showed a distinct peak at 618 nm during the 'severe' episode and a small peak during the 'mild' attack, pointing to the possibility of diagnosing an attack simply by following the fluorometric screen of plasma. 6. The 'severe' attack of coproporphyria was treated with daily infusions of haem arginate, 3 mg/kg, every day for 4 days, at the end of which period a dramatic clinical response was observed. The relief of symptoms was found to be clearly related to the moderate decrease in uroporphyrin excretion observed rather than to the steep decline in the precursors.

Heme synthesis in chronic renal failure: the effects of hemodialysis, peritoneal dialysis and erythropoietin treatment

Increased plasma porphyrins have been described in patients with chronic renal failure (CRF). We measured plasma levels of porphyrins and the activity in erythrocytes of porphobilinogen deaminase (PBG-D), one of the key enzymes in heme biosynthesis, in CRF patients not yet on dialysis and in patients on intermittent hemodialysis (IHD) or chronic ambulatory peritoneal dialysis (CAPD), some of whom were being treated with recombinant human erythropoietin (rHuEPO). In addition, the amount of immuno-detectable PBG-D (Ig PBG-D) per 100 units standard PBG-D activity (Ig PBG-D/100 U) and the total amount of Ig PBG-D, using polyclonal antibodies, were determined in erythrocytes of all patients and controls to detect changes in biodegradation of this enzyme. Plasma porphyrins were increased in CRF patients not yet on dialysis and even higher in both patient groups on dialysis compared with controls. Plasma porphyrins were higher in patients on IHD than in patients on CAPD. The activity of PBG-D was increased and Ig PBG-D/100 U was decreased in patients on IHD compared with CRF patients not yet on dialysis and patients on CAPD. Reticulocyte counts were also greater in patients on IHD than in CRF patients not yet on dialysis and patients on CAPD. Ig PBG-D was increased in both groups of patients on dialysis and treated with rHuEPO compared with patients not treated with rHuEPO.

IN CONCLUSION

(1) in patients on IHD, an increased production of porphyrins is, at least partly, caused by an increased PBG-D activity, and (2) an increased PBG-D activity and a decrease in Ig PBG-D/100 U in patients on IHD could be explained by the presence of a (relatively) young erythroid cell population in which a larger part of PBG-D has not yet been degraded.

A modified spectrophotometric assay for porphobilinogen deaminase: its application in the detection of both carriers and patients with acute intermittent porphyria

A spectrophotometric method for porphobilinogen deaminase assay in erythrocytes is described. This test is determinant for the definite diagnosis of acute intermittent porphyria. In the method described, delta-aminolevulinic acid is used as substrate. Mercaptoethanol and zinc ions are introduced to maintain delta-aminolevulinic acid dehydratase in optimal conditions and to guarantee the in vitro production of porphobilinogen. An incubation temperature of 45 degrees C leads to the production of uroporphyrins, which are measured spectrophotometrically at 405 nm, giving reproducible results. The assay can be performed easily in any clinical laboratory and is valuable for detecting both patients and carriers of acute intermittent porphyria.

Acute intermittent porphyria: clinical analysis of nine cases

BACKGROUND

Acute intermittent porphyria (AIP) is an uncommon disorder, characterized by a variety of nonspecific symptoms and signs. Many patients have undergone prolonged medical care for the condition without accurate diagnosis; some have even received unnecessary operation. Here the clinical features of nine cases are presented.

METHODS

Nine patients with AIP were diagnosed and treated at this hospital during the period for 1986 to 1993. The medical records of these patients were reviewed, and diagnosis of AIP in all cases was confirmed by positive Watson-Schwartz test. In three cases, further confirmation was done with erythrocyte porphobilinogen (PBG) deaminase activity measurement. Patients with photosensitivity were excluded.

RESULTS

All patients presented initially with abdominal pain; two had been operated upon for acute abdomen. Neurological presentations at diagnosis were motor and/or sensory polyneuropathy (6/9), autonomic dysfunction (6/9), mental change (5/9) and seizure (4/9). Two cases had hyponatremia. One patient died of intractable seizures.

CONCLUSIONS

AIP is a frequently forgotten old disease; if not correctly recognized, repeated and unnecessary surgery may occur. However, the diagnosis is easy when the possibility of this disorder is kept in mind.

Influence of protein calorie malnutrition and fasting on the activities of delta-aminolevulinic acid dehydratase and porphobilinogen deaminase in rats

Rats were fed a restricted standard diet (6-8 g daily) for 4 weeks. The erythrocyte activity of delta-aminolevulinic acid dehydratase showed a very expressed decrease (7.9 times) and its hepatic activity diminished more than twice. Porphobilinogen deaminase activity was reduced by 40% and 17% respectively. After a 3-day total food deprivation delta-aminolevulinic acid dehydratase activity remained unchanged in red blood cells, but an increase by 52% was found in the liver. The erythrocyte activity of porphobilinogen deaminase was reduced by 42% and its hepatic activity--by 16%.

Acute intermittent porphyria and mental illness--a family study

All cases of acute intermittent porphyria (AIP) are believed to be caused by a mutation in the gene encoding for porphobilinogen deaminase, a rate-limiting enzyme in the haem synthetic pathway. This gene has been mapped to the long arm of chromosome 11, a region of the genome that has recently attracted considerable attention as a possible location for genes implicated in major mental disorder. This study was designed to show whether major mental illness co-segregated with acute intermittent porphyria in families where the two conditions are found. The study also investigated the relation between clinical mental symptoms and biochemical parameters of acute intermittent porphyria. The case records of 344 consecutive patients admitted to the Porphyrias Research Group in the Western Infirmary in Glasgow between 1950 and 1988 with acute intermittent porphyria were examined for evidence of psychiatric contact. Of 16 individuals identified, 12 were available for the study. Forty relatives of these 12 probands, including 9 who were asymptomatic carriers of AIP, were interviewed for lifetime history of mental illness and current symptoms. Comparisons were made between 4 groups of patients based on urinary porphyrin levels and erythrocyte enzyme activity; 1) manifest acute intermittent porphyria, 2) latent acute intermittent porphyria, 3) normal relatives and 4) total acute intermittent porphyria (latent and manifest combined). No association was found between AIP and schizophrenia or manic-depressive illness. Only one patient with schizophrenia was found in the sample of 344 case notes, and in 2 families bipolar illness was found but did not segregate with acute intermittent porphyria. The commonest psychiatric diagnosis in patients was generalized anxiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental change in activity of red cell porphobilinogen deaminase and its electrophoretic variant in the Japanese population

The activity of porphobilinogen deaminase (PBGD), an enzyme whose partial deficiency is associated with acute intermittent porphyria (AIP), changes during development. Little is known about the postnatal change of PBGD activity and the prevalence of its electrophoretic variant in the Japanese population. The activity of PBGD was measured fluorometrically in 194 infants aged 0-12 months, while isoelectric focusing of PBGD was performed in 400 healthy Japanese adults aged 20-45 years and 30 children with various hematological disorders aged 1-15 years. The PBGD level was 1.9 times higher in the neonates than in the adults, decreased abruptly during the first month of life, and reached the adult level at the age of 9 months. None of the 400 healthy Japanese adults and the 30 children with hematological disorders showed any electrophoretic variant. These results suggest that there is no need to consider any polymorphism in the gene dose study of PBGD and that the biochemical screening of AIP is applicable to since the late infancy.

Heme biosynthesis in uremic patients on CAPD or hemodialysis

We have analyzed some parameters of porphyrin metabolism in 60 patients with end-stage renal failure, 20 of them on CAPD and the remaining on HD. In comparison with 56 control subjects, both groups of patients showed the three following findings: low erythrocyte aminolevulinate dehydrase activity, inhibition ability for the activity of this enzyme when their plasma was incubated in vitro with normal erythrocytes, and increased plasma porphyrin levels. Like anemia, these abnormalities were more remarkable in patients on HD who also exhibited increased erythrocyte protoporphyrin levels and compensatory porphobilinogen deaminase activities. Mean weekly porphyrin removal through dialysate was higher in CAPD (90.8 micrograms) than in HD patients (30.4 micrograms). Dialysate and plasma porphyrins were correlated in both circumstances (r = 0.714, P < 0.01 and r = 0.637, P < 0.05, respectively). The less pronounced porphyrin abnormalities found in CAPD patients with respect to HD patients may be due to the more efficient capability of peritoneal dialysis for removing from plasma protein-bound substances, as porphyrins and inhibitors of aminolevulinate dehydrase or other enzymes involved in erythropoiesis. Since no close relationship was found between these abnormalities of porphyrin metabolism and hematocrit values, the anemia of uremia cannot be merely considered as a direct consequence of altered heme biosynthetic pathway.

[Hyperprolactinemia associated with acute intermittent porphyria]

Galactorrhea as the result of hyperprolactinemia has been described in very rare cases associated to acute outbreaks of intermittent acute porphyria (IAP). In our country, any of such cases have been published or analytically documented. We present the case of a patient admitted in our hospital for the study of abdominal pain and galactorrhea, with latter diagnosis of IAP, supported by the assessment of the activity of the enzyme showing a deficit in the red blood cells.

Genetic carrier detection in Norwegian families with acute intermittent porphyria

Early detection of carriers of acute intermittent porphyria (AIP) is of great value as an assistance for correct diagnosis and prevention of attacks. In order to complement traditional biochemical methods, restriction fragment length polymorphism (RFLP) studies as well as analysis for a previously identified point mutation were included in a study of three Norwegian AIP families. Several asymptomatic carriers could be identified, and the study thus demonstrates the usefulness of the combination of biochemical and genetic analysis.

Childhood porphyrias: implications and treatments

In describing the clinical, biochemical, and family findings in five children with porphyria, we examine initial treatments and, where appropriate, the effectiveness of long-term therapy. We note that porphyria diagnosis, particularly in childhood, relies heavily on specialist laboratory investigations. Because disease expression in some porphyrias requires exposure to precipitating factors, it may be prevented or delayed by their avoidance.

Frequency of low erythrocyte porphobilinogen deaminase activity in Finland

The frequency of low erythrocyte porphobilinogen deaminase (PBGD) activity was investigated in 2234 blood donors and in 30 patients with acute intermittent porphyria. The mean enzyme activities (+/- SD) were 3.38 +/- 0.58 U and 1.82 +/- 0.41 U, respectively. Eighteen blood donors without any history of symptoms of porphyria or haematological disease had low PBGD activity (less than 2.20 U), and they were studied further. All of them also had subnormal concentrations of the erythrocyte enzyme protein, as determined by an immunological method. Lymphocyte PBGD activity was within the normal range, but this parameter does exhibit a wide overlap between normal and porphyric values. Urinary excretion of porphobilinogen was moderately increased in two of the blood donors. In four of the 18 families of the blood donors with low PBGD activity several first-degree relatives had low erythrocyte enzyme activity, consistent with a dominant mode of inheritance. The 5-aminolaevulinic acid loading-test was normal in the blood donors with familial occurrence of low erythrocyte PBGD. It is concluded that inherited defects in erythrocyte PBGD occurred among Finnish blood donors with a frequency of about 1 in 500. The defects may be identical with those in acute intermittent porphyria (AIP), but other mechanisms are also possible, e.g. a mutation in the erythroid-specific part of the PBGD gene.

Denaturing gradient gel electrophoresis for rapid detection of latent carriers of a subtype of acute intermittent porphyria with normal erythrocyte porphobilinogen deaminase activity

Acute intermittent porphyria is an autosomal dominant disorder defined by a partial deficiency of porphobilinogen deaminase (EC 4.3.1.8). Clinical manifestations of the disease are characterized by acute attacks of neurological dysfunction often linked to environmental factors. Early diagnosis of gene carriers is important in the prevention of attacks and is usually achieved by determining the porphobilinogen deaminase activity in erythrocytes. However, in a subtype of acute intermittent porphyria, the enzymatic defect is restricted to nonerythropoietic cells. Different mutations have already been described that account for this phenotype in two unrelated families. We previously detected asymptomatic carriers by using mutation-specific probes after in vitro amplification of the target DNA sequence. In this study, we investigated the DNA of eight unrelated subjects with the same subtype of acute intermittent porphyria by using the polymerase chain reaction, with subsequent analysis of the amplified products by denaturing gradient gel electrophoresis. Five of these patients shared the same single-base change. This technique was quite simple and efficient for detecting asymptomatic carriers. Importantly, it is potentially useful for studying families with the same phenotypic subtype of the disease and possibly different mutations in the same DNA region.

High-performance liquid chromatographic detection of pitfalls in porphobilinogen deaminase determination

Potential pitfalls in the determination of porphobilinogen deaminase activity, as well as ways of eliminating these sources of error and determining the activity accurately, are discussed. In addition to measurement of the accurate activity, the described method (a combination of incubation of homogenate with porphobilinogen and high-performance liquid chromatographic separation) can also be used to detect enzymic defects in the haem biosynthetic pathway, according to the pattern of accumulation of the various porphyrins.

[An effect of aluminum on hemesynthesis--special reference to erythrocyte uroporphyrinogen--1--Synthetase and protoporphyrin]

In order to evaluate an inhibitory effect of Al on haem synthesis, erythrocyte uroporphyrinogen-1-synthetase (RBC-Uro-S) activity and erythrocyte level of protoporphyrin (RBC-protoporph) were measured and compared with RBC-Al in 22 patients on maintenance hemodialysis. RBC-Uro-S activity was varied from 38 to 83 nM/ml RBC/hr 37 degrees C (54.18 +/- 12.42 nM/ml RBC/hr 37 degrees C) and a slight elevation could be found no more than in two cases. On the other hand, RBC-protoporph levels showed to be significantly elevated in many cases such as 8 cases out of 22 (36.4%). (normal subjects: 63.25 +/- 27.61 micrograms/dl RBC, HD patients: 90.0 +/- 28.35 micrograms/dl RBC). This study failed to confirm a significant negative correlation between RBC-Al and RBC-Uro-S activity, but a positive significant correlation could be found between RBC-Al and protoporphyrin levels. However we could confirm a negative correlation neither between RBC-Al and Hb values nor between RBC-Uro-S activity and Hb values. Therefore we concluded that Al-intoxication in the patients on long term hemodialysis had a definite inhibitory effect on heme synthesis, but it was by no means a major factor in pathogenesis of anemia associated with chronic dialysis.

Assignment of human porphobilinogen deaminase to 11q24.1----q24.2 by in situ hybridization and gene dosage studies

In situ hybridization and gene dosage-effect studies were conducted to determine the detailed chromosomal location of the gene encoding human porphobilinogen deaminase (PBGD). Red cell PBGD activity was normal in one patient with monosomy for 11q24.2----qter but was increased 1.5 times in another patient with trisomy for 11q22.2----qter. The cDNA probe for PBGD was found to be specifically hybridized to band 11q24. These results suggest that the gene for PBGD is localized within the region 11q24.1----q24.2.

A new method for isolation of reticulocytes: positive selection of human reticulocytes by immunomagnetic separation

A method for isolating pure reticulocytes from leukocyte-depleted blood of normal persons is presented. The separation was achieved using an immunomagnetic technique. A monoclonal mouse antibody against human transferrin receptor was bound to magnetic beads conjugated with sheep antimouse antibody. The recovery of reticulocytes from peripheral blood was 15% to 42%. Blood used for isolation of reticulocytes could be stored for 4 days at 22 degrees C without altering the yield of reticulocytes. At 37 degrees C incubation, the reticulocytes matured rapidly and the transferrin receptor was found to have a half-life of 16 hours. The activity of several enzymes and the amount of creatine and hemoglobin A1C were measured both in the reticulocytes and peripheral blood. Of the enzymes, porphobilinogen deaminase had the best discriminatory power with a ratio of 8.8 between reticulocytes and peripheral red blood cells. The ratio for creatine was 16.7. The ability to isolate pure human reticulocytes, released after normal erythropoiesis, will offer new possibilities in the study of these cells.

High performance liquid chromatographic studies of erythrocytes haem biosynthetic enzyme activities in alcoholic macrocytosis

The activities of 5-aminolaevulinate dehydrase (ALA-D), hydroxymethylbilane synthase (HMB-S), uroporphyrinogen III synthase (URO-S) and uroporphyrinogen decarboxylase (URO-D) in the erythrocytes of alcoholics were assayed and compared with those in controls and abstaining alcoholics. The HMB-S and URO-S activities in alcoholics were significantly higher than the controls and there were significant correlations between enzyme activities and mean corpuscular volume (MCV). Alcoholics abstaining from alcohol over a nine-month period showed a return to normal enzyme activities in parallel with the normalization of their MCV. Abstaining alcoholics thus all had normal HMB-S and URO-S activities. The ALA-D and URO-D activities of alcoholics were not significantly different from controls or from abstaining alcoholics. Alcohol appears to have a selective effect on the haem biosynthetic enzymes in the erythron.

Erythrocyte porphobilinogen deaminase activity in porphyria cutanea tarda

Porphyria cutanea tarda (PCT) results from a metabolic block in heme synthesis at the level of uroporphyrinogen decarboxylase. We measured the activity of one of the enzymes preceding it in the heme biosynthetic pathway, porphobilinogen deaminase (PBGD; EC 4.3.1.8), in erythrocytes of 47 patients with symptomatic or asymptomatic familial or sporadic PCT. PBGD activity was significantly increased in all four PCT groups, compared with controls. To study the mechanism of this increased PBGD activity, we determined, using polyclonal antibodies, the amount of immuno-detectable PBGD per 100 units of PBGD activity (Ig PBGD/100 U) and the total amount of immuno-detectable PBGD (Ig PBGD) in erythrocytes from all 47 patients and from controls. In both familial and sporadic PCT, Ig PBGD/100 U was decreased compared with that in controls (P less than 0.05). Especially in asymptomatic patients of the familial PCT group there was an inverse correlation between increasing PBGD activity and Ig PBGD/100 U (r = -0.90). In familial PCT, and to a minor degree in sporadic PCT, an increase in PBGD activity was accompanied by an increased Ig PBGD, compared with controls (familial PCT: P less than 0.001, sporadic PCT: P less than 0.05). In familial and sporadic PCT an increase in erythrocyte PBGD activity can, at least partly, be explained by a diminished degradation of PBGD. In familial PCT, in the symptomatic group more than in the asymptomatic group, and to a minor degree in sporadic PCT, there is in addition an increase in the absolute amount of PBGD.