V. E Parera

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.

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%).

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.

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. Hum Mutat 14:355, 1999.

Amiodarone is a pharmacologically safe drug for porphyrias

Amiodarone (AD) is an effective antidysrythmic drug, however, there can be serious side effects, such as hepatic and neurological alterations, as well as skin photosensitization, as seen in porphyrias. Clinical signs in porphyrias might be triggered by the so-called porphyrinogenic drugs. Without sound basis, Amiodarone has been classified as an unsafe drug for porphyric patients. The aim of this work has been to study the effect of AD, both in vivo and in vitro, on heme metabolism. In the in vivo assays, the activities of 5-aminolevulinate synthetase (ALA-S), ALA dehydratase (ALA-D), porphobilinogenase (PBGase) and PBG-deaminase (PBG-D) in blood, liver, and kidney; hepatic and fecal porphyrins, urinary ALA, PBG and porphyrins in male mice strain CF1 treated with AD (100 mg i.p. daily) for 1 week and 1 month, were measured. No significanat differences were found for any of these parameters in the AD treated animals as compared to controls. In the in vitro experiments human blood, and mice blood, liver, and kidney, were used to measure the activities of ALA-S, ALA-D, PBGase, PBG-D and uroporphyrinogen decarboxylase, in the presence of varying concentrations of AD (0.0172-4.304 mM). AD did not modify any of the enzyme activities. All of the above biochemical parameters were studied in 17 cardiac patients under AD treatment for 3 to 20 years. Neither the activities of the heme enzymes, nor the levels of precursors and porphyrins in urine and plasma were altered. These findings clearly demonstrate that AD is a pharmacologically safe drug and can be used for the treatment of associated pathologies in porphyrias.