An odd case of heteroallelic acute intermittent porphyria in the Argentinean population

AIP is an acute liver disorder caused by a deficiency of porphobilinogen deaminase (PBGD) characterized by neuroabdominal symptoms. It is an autosomal dominant disease. However, homozygous dominant AIP (HD-AIP) have been described. In some cases erythrodontia was observed. CEP is an autosomal recessive disease produced by mutations in the uroporphyrinogen III synthase gene (UROS), characterized by severe cutaneous lesions and erythrodontia. The aim of the work was to establish the differential diagnosis of porphyria in a patient with abdominal pain, neurological attacks, skin symptoms and erythrodontia. The PBGD activity was reduced 50% and the genetic analysis indicated the presence of two genetic variants in the PBGD gene, p.G111R and p.E258G, a new genetic variant, revealing a case of heteroallelic HD-AIP. The patient, first diagnosed as a carrier of a dual porphyria: AIP / CEP based on the excretion profile of porphyrins, precursors and her clinical symptoms, would be an atypical case of human HD-AIP. These results would also suggest the presence of a phenocopy of the CEP, induced by an endogenous or exogenous factor. Our findings highlight the importance of genetic studies for a proper diagnosis of porphyria, prevention of its manifestation and its treatment.

The very first description of a patient with hepatoerythropoietic porphyria in Argentina. Biochemical and molecular studies

Hepatoerythropoietic Porphyria (HEP) is the rare homozygous form of Porphyria Cutanea Tarda (PCT). It is characterized clinically by the early onset of severe skin manifestations which can be confused with Congenital Erythropoietic Porphyria (CEP) or with PCT when the symptoms are mild. We describe the case of a 14 year-old child with skin manifestations similar to those observed in PCT. The biochemical assays ruled out a CEP as well as they suggested the development of a HEP. Although his symptoms were not severe enough to be HEP, the enzymatic activity was dramatically reduced to a 5% of normal values and the molecular analysis revealed the presence of two already known different mutations on the patient's URO-D gene, c.703 C>T and IVS9-1. Each parent carry one of the mutations, but they were absent in the brother. This is the first Argentinean HEP case ever described which appeared in a compound heterozygous form and less residual URO-D activity but associated to a mild phenotype.

Acute porphyrias in the Argentinean population: a review

The porphyrias are a group of inherited metabolic disorders of heme biosynthesis which result from a partial deficiency in one of its seven specific enzymes, after its first and rate limiting enzyme, delta-aminolevulinic acid synthetase. They can be classified on the basis of their clinical manifestations into cutaneous, acute and mixed disorders. Acute intermittent porphyria (AIP) is the most common type of hepatic acute porphyrias, inherited as an autosomal dominant trait, caused by a defect in the gene which codifies for the heme enzyme porphobilinogen deaminase. Its prevalence in the Argentinean population is about 1:125,000. A partial deficiency in another enzyme, protoporphyrinogen oxidase, produces variegate porphyria (VP), the second acute porphyria most frequent in the Argentinean population (1:600,000). Here, we review all the mutations we have found in 46 AIP and 9 VP unrelated Argentinean patients. To screen for mutations in symptomatic patients, we have proposed a geneticresearch strategy.

Identification and characterization of two novel mutations that produce acute intermittent porphyria: A 3-base deletion (841-843delGGA) and a missense mutation (T35M)

A partial deficiency of Porphobilinogen deaminase (PBGD) is responsible for acute intermittent porphyria (AIP). AIP is inherited in an autosomal dominant fashion, and the prevalence in the Argentinean population is about 1:125,000. Here, two new mutations and two previously reported were found in the PBGD gene in 22 Argentinean AIP patients corresponding to 8 different families. To screen for AIP mutations in symptomatic patients, genomic DNA isolated was amplified in 6 PCR reactions, then all coding exons and flanking intronic regions were sequenced. The novel mutations are 841-843delGGA in exon 14, which results in the loss of glycine-281 (G281del), and one 104C>T point mutation in the exon 4 (T35M). To further characterize both novel mutations, the pKK-PBGD construct for the mutant alleles were expressed in E. coli, the enzymatic activity of the recombinant proteins were 1% and 4% of the mean level expressed by the normal allele for 841-843delGGA and T35M, respectively. Hum Mutat 16:373, 2000.

Identification and characterization of hydroxymethylbilane synthase mutations causing acute intermittent porphyria: evidence for an ancestral founder of the common G111R mutation

Acute intermittent porphyria (AIP), the most common hepatic porphyria, results from the half-normal activity of hydroxymethylbilane synthase (HMB-synthase; EC 4.3.1.8), the third enzyme in the heme biosynthetic pathway. Because life-threatening acute neurologic attacks of this autosomal dominant disease are triggered by various ecogenic factors (e.g., certain drugs, hormones, alcohol, and starvation), efforts have been directed to identify and counsel presymptomatic heterozygotes in affected families to avoid the precipitating factors. Thus, to determine the nature of the mutations causing AIP in 26 unrelated enzyme-confirmed patients from Argentina, a long-range polymerase chain reaction method was developed to amplify the entire 10-kb gene in two fragments for efficient cycle sequencing and mutation detection. Eight new mutations were identified including two missense mutations (Q34P and G335S), four small deletions (728delCT, 815delAGGA, 948delA, and 985del12), a single base insertion (666insA), and a splice site mutation (IVS12(+1)). In addition, five previously reported mutations (G111R, R173W, Q204X, R201W, and 913insC) were detected. Notably, G111R was identified in 12 of the 26 (46%) presumably unrelated propositi; however, haplotype analysis with intragenic and flanking markers indicated an ancestral founder. Expression of the two new missense mutations (Q34P and G335S) in f1 E. coli resulted in 2.5% or less of the normal expressed enzyme, confirming their defective function. Thus, eight new and five previously reported HMB-synthase mutations, including a common lesion, were detected, permitting accurate identification and counseling of presymptomatic carriers in these 26 unrelated Argentinean AIP families with this dominant porphyria.

Acute intermittent porphyria: characterization of two novel mutations in the porphobilinogen deaminase gene, one amino acid deletion (453-455delAGC) and one splicing aceptor site mutation (IVS8-1G>T)

A partial deficiency of Porphobilinogen deaminase (PBG-D) is responsible for acute intermittent porphyria (AIP). AIP is inherited in an autosomal dominant fashion, and the prevalence in the Argentinean population is about 1:125,000. Here, two new mutations and three previously reported were found in the PBG-D gene in 12 Argentinean AIP patients corresponding to 5 different families. To screen for AIP mutations in symptomatic patients, genomic DNA isolated was amplified in 2 Multiplex PCR reactions, then all coding exons and flanking intronic regions were sequenced. The new mutations are 453-455delAGC in exon 9 which results in the loss of an alanine residue at position 152, and one new point mutation in the splicing aceptor site in the last position of intron 8 (IVS8-1G>T) which leds to a 15 bp deletion because a cryptic site (first AG upstream) is used. Both mutations produce amino acid deletion without frameshift effect. To further characterize the 453-455delAGC mutation, the pKK-PBGD construct for the mutant allele was expressed in E. coli, the enzymatic activity of the recombinant protein was 1.3% of the mean level expressed by the normal allele. Finally, three missense mutations, previously reported, were identified in three unrelated families.

Acute intermittent porphyria: biochemical and clinical analysis in the Argentinean population

Acute intermittent porphyria (AIP) is the most common type of hepatic acute porphyria. In this work, we have analyzed the biochemical data of all Argentinean AIP families studied in the Porphyrins and Porphyrias Research Centre (CIPYP). We have shown that: (i) the prevalence for this population is about 1:125,000; (ii) the disease is more frequent in women than in men (7:3); (iii) about 60% are latent carriers; (iv) 15% of patients with symptomatic AIP died during an acute attack; (v) the most important precipitating factors of acute attacks in our population were the ingestion of therapeutic drugs (25%), anesthetics in surgical interventions (25%) and infections (20%); (vi) the initial symptom in Argentinean AIP individuals is severe abdominal pain (100%), and it is often accompanied by constipation (37%), anorexia (37%) and tachycardia (30%); and (vii) the percentage of recurrence of the acute attacks is high (81%).

Familial porphyria cutanea tarda: characterization of seven novel uroporphyrinogen decarboxylase mutations and frequency of common hemochromatosis alleles

Familial porphyria cutanea tarda (f-PCT) results from the half-normal activity of uroporphyrinogen decarboxylase (URO-D). Heterozygotes for this autosomal dominant trait are predisposed to photosensitive cutaneous lesions by various ecogenic factors, including iron overload and alcohol abuse. The 3.6-kb URO-D gene was completely sequenced, and a long-range PCR method was developed to amplify the entire gene for mutation analysis. Four missense mutations (M165R, L195F, N304K, and R332H), a microinsertion (g10insA), a deletion (g645Delta1053), and a novel exonic splicing defect (E314E) were identified. Expression of the L195F, N304K, and R332H polypeptides revealed significant residual activity, whereas reverse transcription-PCR and sequencing demonstrated that the E314E lesion caused abnormal splicing and exon 9 skipping. Haplotyping indicated that three of the four families with the g10insA mutation were unrelated, indicating that these microinsertions resulted from independent mutational events. Screening of nine f-PCT probands revealed that 44% were heterozygous or homozygous for the common hemochromatosis mutations, which suggests that iron overload may predispose to clinical expression. However, there was no clear correlation between f-PCT disease severity and the URO-D and/or hemochromatosis genotypes. These studies doubled the number of known f-PCT mutations, demonstrated that marked genetic heterogeneity underlies f-PCT, and permitted presymptomatic molecular diagnosis and counseling in these families to enable family members to avoid disease-precipitating factors.

In inherited porphyrias, lead intoxication is a toxogenetic disorder

1. delta-Aminolevulinic acid dehydratase (ALA-D), blood lead and several enzymes and metabolites of the heme biosynthetic pathway were measured in a number of symptomatic porphyric patients, 22 with acute intermittent porphyria, three with hereditary hepatic coproporphyria, 10 with hereditary porphyria cutanea tarda, two with erythropoietic protoporphyria and two with congenital erythropoietic porphyria and in 84 lead intoxicated persons. 2. In the 39 individuals suffering from the inherited porphyrias and in 32 lead poisoned patients with a 30-50% reduced deaminase, blood lead content was not sufficiently increased (average 28 micrograms%) to account for the greatly decreased activity of ALA-D (average 36% of controls). 3. After a relatively trifling lead exposure they developed the signs of acute lead intoxication. 4. A second group of lead intoxicated patients showing low ALA-D activity and corresponding high concentration of lead in blood, exhibited no other physiologic deviation in the enzymes and metabolites of porphyrin biosynthesis. 5. Individuals with inherited porphyrias are ultrasensitive to low level lead exposure and that lead would also act as a triggering factor. In these patients, lead intoxication can be considered a toxogenetic disorder. 6. An inversely linear correlation between ALA-D activity and blood lead content was obtained for both groups of lead intoxicated patients, however, a different constant (k) for each was obtained, which we have taken as a measure of lead toxogeneticity: k = 10 +/- 1 for lead intoxicated individuals with otherwise normal heme metabolism and k = 5 +/- 0.5 for lead intoxicated symptomatic porphyric patients. 7. Determination of erythrocytic ALA-D, besides blood lead, will be a valuable indicator for preventive medical care for these patients, when they are expected to be exposed to lead either environmentally or in their professional life.

Acquired and inherited porphyria: clinical and biochemical features

Inheritance in 30 cases of porphyria cutanea tarda (PCT) and their relatives was investigated. Seventeen families were studied using the clinical criteria, quantitation, and thin layer chromatography of urinary porphyrins. Thirteen families (13 propositus and 48 relatives) were investigated by using the above criteria and in vitro porphyrin biosynthesis by erythrocytes from delta-aminolevulinic acid. Three different types of PCT were identified: overt, subclinical, and latent. Among 61 members examined, 13 had overt PCT. In six families, ten members had subclinical PCT and six latent PCT showing that in these six families PCT was a hereditary disorder. In seven other families inheritance could not be demonstrated.