Hyperinsulinemia in acute intermittent porphyria

Diabetic oral glucose tolerance test together with hyperinsulinemia in a patient with decompensated acute intermittent porphyria is contrasted to normal findings in compensated acute intermittent porphyria (AIP). Results point to the essential role of insulin for the depression of porphyrin precursor overproduction as a mediator of the "glucose effect".     

High prevalence of a point mutation in the porphobilinogen deaminase gene in Dutch patients with acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by a deficiency of porphobilinogen deaminase (PBGD). Up to now 14 different mutations have been described. In an effort to investigate the molecular epidemiology of AIP we have undertaken a systematic study of different exons of the PBGD gene from a large number of unrelated patients. Here, exon 8 from 82 unrelated Dutch and French AIP patients was examined using single strand confirmation polymorphism analysis (SSCP) after polymerase chain reaction (PCR) amplification. A single base mutation, C to T, at position 346 of the sequence coding for PBGD was observed in 15 Dutch families but in only 1 French family. A simple PCR assay is described to facilitate the diagnosis of this common mutation at the DNA level.     

Three new mutations in the porphobilinogen deaminase gene, detected in acute intermittent porphyria patients from Russia]

Porphobilinogen deaminase (PBGD) is a key enzyme of the heme biosynthetic pathway. Defects in the PBGD gene lead to an autosomal dominant disease, acute intermittent porphyria (AIP). Almost all AIP patients with rare exceptions are heterozygous for the defective gene. To date, at least 160 different mutations causing AIP are identified. Extensive investigations along this line are conducted in many countries of the world. In Russia these studies had not been hitherto performed. Here we report the results of molecular genetic examination of four Russian patients with AIP diagnosed from clinical symptoms. By direct sequencing of the PBGD gene or the corresponding cDNA, we have detected four mutations, three of which were not previously encountered in the world population. These are TAAG deletion in intron 7 between positions +2 and (IVS7 2-5 delTAAG); T deletion in the initiation codon ATG of exon 3, and the G for C replacement at position -1 of intron 5 (IVS5 as -1 G:C), which disrupts splicing. In addition, in one female patient, a known deletion CT in codon 68 was revealed. In two patients, expression of PBGD gene alleles was significantly disproportional, so that normal mRNA prevailed in one case and mRNA of nonerythroid type in the other. Deletion in intron 7 was easily detectable due to the formation of a heteroduplex fragment with abnormal electrophoretic mobility directly in PCR. This simple heteroduplex analysis allowed us to exclude AIP carriage in son and daughter of a female patient with the genetic defect.     

Uroporphyrinogen-I-synthetase in erythrocytes in acute intermittent porphyria

The primary genetic defect in acute intermittent porphyria is a decreased uroporphyrinogen I-synthetase [EC.4.3.1.8] activity. As a beginning of a genealogical study of the known families with members suffering from this disease in the People's Republic of Bulgaria, the red cell uroporphyrinogen I-synthetase was determined in 3 families by the method of Mandel et al [8]. Except for the three propositi, an enzyme deficiency was established in 3 latent carriers of the pathological gene, two of whom had normal values of the urinary epsilon-aminolevulinic acid and porphobilinogen. The determination of red cell uroporphyrinogen I-synthetase proved to be a valuable parameter for revealing the latent AIP.     

Detection of eleven mutations causing acute intermittent porphyria using denaturing gradient gel electrophoresis

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by mutations of the gene coding for porphobilinogen deaminase (PBGD). Until now, sixteen different mutations have been described. In an effort to investigate further the molecular epidemiology of AIP, we have undertaken a systematic study of different exons of the PBGD gene from a large number of unrelated patients. Here, we have examined seven of the fifteen exons of the gene from 43 unrelated Dutch and French AIP patients using denaturing gradient gel electrophoresis after polymerase chain reaction amplification. Eleven new mutations were found, accounting for the enzymatic defect in about half of the patients. This study further documents the molecular heterogeneity of the mutations responsible for AIP and describes an efficient strategy to detect the mutations in patients with previously unknown abnormalities.     

Enzyme aspects of acute intermittent porphyria

Summary Patients with acute intermittent porphyria are now known to have a decrease of the third enzyme and, in liver, an increase of the first enzyme of the heme biosynthetic pathway. It is possible that the induction of the first enzyme (ALA synthetase) in the liver of these patients results from the partial block in heme synthesis, since heme is known to be involved in the repression of hepatic ALA synthetase via a closed negative feedback loop. Presumably, an increase of hepatic ALA synthetase allows the delivery of a higher substrate concentration to the enzyme at the level of the block, thus raising the rate of the synthesis of end product toward normal. Using a simplified Michaelis-Menten model of an irreversible pathway in a homogeneous system, quantitative relationships between the degree of block and the magnitude of induction of the first enzyme necessary to return the steady state rate of the pathway to normal have been developed. This is intended as a point of departure for refinements which may ultimately lead to more accurate quantitative relationships.Despite the fact that various forms of experimental porphyria do not produce the specific enzyme decrease of acute intermittent porphyria, they have provided the basis for a number of discoveries which have direct application to this disease.Reprint requests should be sent to this address.     

RFLP analysis of three different types of acute intermittent porphyria

Summary Restriction fragment length polymorphism (RFLP) analysis was performed in three Finnish families with different subtypes of acute intermittent porphyria (AIP): 1) cross-reacting immunological material (CRIM)-negative with low erythrocyte porphobilinogen (PBG)-deaminase activity, 2) CRIM-positive with low PBG-deaminase activity and 3) CRIM-negative with normal PBG-deaminase activity. The disease-associated RFLP haplotype (A2B1C2) of the PBG-deaminase gene was the same in each family. In all three families, RFLP linkage analysis resulted in highly positive lod scores. The maximal lod score (4.3) was obtained at the recombinant fraction of zero, thus confirming a tight linkage of AIP to the PBG-deaminase locus. Of the 62 family members tested, 30 had the disease-associated haplotype; in 5 of them, conventional tests for AIP were normal and in one, uncertain. RFLP analysis can thus reveal new gene carriers and help in the diagnosis of individuals with uncertain results in other laboratory tests.     

Molecular basis of acute intermittent porphyria

Acute intermittent porphyria is an inherited disease of haem biosynthesis that results from mutation of the gene for the enzyme porphobilinogen deaminase. Many different mutations have been located throughout the gene. The three-dimensional structure of the enzyme helps in understanding how these mutations lead to inactivation even when, in some cases, the mutated product is abundant and folded correctly.     

Heteroduplex mobility assay detects DNA mutations for differentiation of closely related phytoplasma strains

We present the first use of DNA heteroduplex mobility assay (HMA) to detect the point mutations including substitutions and deletions/insertions in 16S rDNA of aster yellows phytoplasma (AY27) and to differentiate phytoplasmas collected from field samples of clover proliferation (CP) and alfalfa witches'-broom (AWB). The phytoplasmal 16S rDNA fragment was amplified from AY27 by polymerase chain reaction (PCR) and cloned into a plasmid vector. The cloned DNA fragment was subjected to in vitro mutation to produce 1- to 4-base substitutions and 1- to 3-base deletions. The mutated 16S rDNA fragments were analyzed by HMA. The results showed that a single two-base substitution or a single-base deletion/insertion in the 529 bp DNA fragment was directly detected and that a DNA divergence at a level of as low as 0.2% was detectable by HMA. Heteroduplex mobilities were affected by the number and composition of the phytoplasma DNA bases in mismatches or gaps and were proportional to the degree of DNA divergences. Gaps caused greater retardation in heteroduplex mobility than mismatches did. HMA was highly sensitive in detecting the mixed infections of phytoplasmas. In analyses of CP and AWB field samples collected in Alberta, two CP and one AWB phytoplasma isolates were differentiated from others by HMA but not by restriction fragment length polymorphism (RFLP). Therefore, HMA provides a simple, rapid, highly sensitive and analytical method to detect and estimate the genetic divergence of phytoplasmas when other methods such as RFLP are not readily applicable.     

Genetic heterogeneity in acute intermittent porphyria: characterisation and frequency of porphobilinogen deaminase mutations in Finland.

The occurrence of different porphobilinogen deaminase mutant types in 68 patients with acute intermittent porphyria from 33 unrelated families in Finland was studied with biochemical and immunological techniques. In this fairly homogenous population four different porphobilinogen deaminase mutant types were identified and their frequencies determined. Most (about 80%) of the mutations were cross reacting immunological material (CRIM) negative, including a large kindred with normal erythrocyte porphobilinogen deaminase activities. The remainder of the families had CRIM positive mutations, including an unusual type (type 2) that had an immunoreactive, non-catalytic porphobilinogen deaminase level considerably greater than the maximal theoretical ratio of CRIM to activity of 2.0 for a single mutant allele. Correlations of the amount of residual porphobilinogen deaminase activity and the occurrence of acute clinical manifestations in each mutant type suggested that CRIM positive type 2 patients may have fewer acute symptoms.     

High frequency of mutations in exon 10 of the porphobilinogen deaminase gene in patients with a CRIM-positive subtype of acute intermittent porphyria.

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by a partial deficiency of porphobilinogen (PBG) deaminase. Different subtypes of the disease have been defined, and more than 10 different mutations have been described. We focused our study on exon 10, since we previously found that three different mutations were located in this exon and that two of them seemed to be relatively common. We used denaturing gradient gel electrophoresis (DGGE) after in vitro amplification to detect all possible mutations in exon 10 in 41 unrelated AIP patients. In about one-fourth of these patients we could distinguish three abnormal migration patterns, indicating the presence of various mutations. Additional sequencing demonstrated the presence of three different single-base substitutions. Two of these mutations had already been described. A third one consisted of a C-to-T transition located at position 499 of the PBG deaminase mRNA and resulted in an Arg-to-Trp substitution. All three mutations were found in patients with cross-reacting immunological material (CRIM)-positive forms of AIP. The high frequency of these mutations make DGGE analysis of exon 10 a useful approach allowing the direct direction of the DNA abnormality in most of the families with the CRIM-positive subtype of AIP.     

Identification and expression of mutations in the hydroxymethylbilane synthase gene causing acute intermittent porphyria (AIP)

BACKGROUND: Acute intermittent porphyria (AIP), an autosomal dominant inborn error, results from the half-normal activity of the heme biosynthetic enzyme hydroxymethylbilane synthase (EC 4.3.1.8; HMB-synthase). This disease is characterized by acute, life-threatening neurologic attacks that are precipitated by various drugs, hormones, and other factors. The enzymatic and/or biochemical diagnosis of AIP heterozygotes is problematic; therefore, efforts have focused on the identification of HMB-synthase mutations so that heterozygotes can be identified and educated to avoid the precipitating factors. In Spain, the occurrence of AIP has been reported, but the nature of the HMB-synthase mutations causing AIP in Spanish families has not been investigated. Molecular analysis was therefore undertaken in nine unrelated Spanish AIP patients. MATERIALS AND METHODS: Genomic DNA was isolated from affected probands and family members of nine unrelated Spanish families with AIP. The HMB-synthase gene was amplified by long-range PCR and the nucleotide sequence of each exon was determined by cycle sequencing. RESULTS: Three new mutations, a missense, M212V; a single base insertion, g4715insT; and a deletion/insertion, g7902ACT-->G, as well as five previously reported mutations (G111R, R116W, R149X R167W, and R173W) were detected in the Spanish probands. Expression of the novel missense mutation M212V in E. coli revealed that the mutation was causative, having <2% residual activity. CONCLUSIONS: These studies identified the first mutations in the HMB-synthase gene causing AIP in Spanish patients. Three of the mutations were novel, while five previously reported lesions were found in six Spanish families. These findings enable accurate identification and counseling of presymptomatic carriers in these nine unrelated Spanish AIP families and further demonstrate the genetic heterogeneity of mutations causing AIP.