Biomedical subjects
Publications and source records attributed to B Grandchamp.
Explore the source record for details and available documents.
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.
Quantification of specific RNA or DNA molecules that are present in minute amounts in biological samples has previously been performed using PCR in the presence of an internal standard. We have adapted this concept by introducing several modifications that facilitate the quantification of the products and obviate the need for radioisotopes. After amplification, individual products are separated on sequencing gels and directly quantified using a fluorescent automated DNA sequencer. We describe two applications of this approach: the quantitation of minute amounts of bcr-abl hybrid mRNA from malignant cells and the determination of gene copy number in cells stably transfected with a plasmid bearing a chloramphenicol acetyltransferase gene.
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.
The molecular basis of the ferrochelatase defect responsible for human Erythropoietic Protoporphyria (EPP), a usually autosomal dominant disease, was investigated in a family with an apparently homozygous patient. Two mutations of the ferrochelatase gene were identified by sequencing the proband's cDNA after in vitro amplification of the mRNA and subcloning of the amplified products. One mutation results from a G to T transition at nucleotide 163 which produces a glycine to cysteine substitution at amino-acid residue 55 (G-55-C). The other one was a G to A change at nucleotide 801, leading to a methionine to isoleucine substitution at amino-acid residue 267 (M-267-I). This EPP patient was then double heterozygous and as expected each of his parents carried one of the mutations. A second similar EPP patient was screened for these mutations with negative results, showing a genetic heterogeneity in EPP.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Porphobilinogen deaminase, the third enzyme in the heme biosynthetic pathway, is encoded by a gene having two different promoters. Differential splicing of transcripts from the promoters yields two distinct mRNA species that are translated to give two isoforms of the protein. One isoform is ubiquitous, whereas the other is erythroid-specific. In this study, we have analyzed the gene regulatory elements that contribute to the tissue-specific promoter utilization of the mouse porphobilinogen deaminase gene. Six nuclear DNase I-hypersensitive sites were mapped in erythroid and nonerythroid cells, and four of these regions were further analyzed for in vitro nuclear protein-binding sites. The erythroid-specific promoter contains three erythroid nuclear factor GF-1-binding sites. The proximal GF-1-binding site, together with an adjacent duplicated CACCC motif, was sufficient to confer erythroid-specific expression in functional studies. Furthermore, as upstream gene sequences were shown to greatly increase promoter activity in erythroid cells, it suggests an upstream erythroid-specific enhancer may also be required for the up-regulation of the erythroid-specific promoter during erythropoiesis.
Explore the source record for details and available documents.
Acute intermittent porphyria (AIP) is an autosomal dominant metabolic disorder affecting the enzyme porphobilinogen (PBG) deaminase in the heme biosynthetic pathway. The highest prevalence of the disorder has been observed in Scandinavia, especially in northern Sweden (Lappland) where it occurs with a prevalence of 1 in 1500. Biochemical assays of the activity and concentration of PBG deaminase in red blood cells, haplotyping with 4 intragenic restriction fragment length polymorphisms (RFLPs) (MspI, PstI, BstNI, ApaLI) using the polymerase chain reaction (PCR) and screening for known base substitutions by oligonucleotide probes was performed in 28 Swedish AIP families. There was no close relationship between haplotype, biochemical findings (PBG deaminase activity, enzyme-linked immunosorbent assay [ELISA], and excess urinary excretion of delta-aminolevulinic acid or PBG), and a specific mutation. Three different haplotypes were identified. The haplotype 2/1/1/2 (MspI/PstI/BstNI/ApaLI; +/-/-/+) was found to be the most frequent among gene carriers (P less than 0.001). The disease segregated with the haplotype 2/1/1/2 in the 10 families originating from northern Sweden. All 28 families were screened for three known point mutations. Only one was found to carry one of these mutations. Thus, the genetic background of AIP is heterogeneous in Sweden.
Human and rodent genomes contain multiple copies of ferritin H and L subunit sequences, although it is not yet clear whether there is more than one expressed gene for either of these subunits. We have isolated a cDNA corresponding to mouse ferritin H subunit and observed that the mouse genome contains three to four H-related sequences. This cDNA was used to establish the genomic location of mouse ferritin H subunit genes by chromosomal in situ hybridization. Metaphase chromosomes of concanavalin A-stimulated lymphocytes from a WMP male mouse were examined by in situ hybridization with 3H-labeled cDNA and the chromosomes were identified by R banding (fluorochrome-photolysis-Giemsa method). The results indicate that mouse ferritin H-related sequences map at chromosomes 3, 6, and 19. Homology of synteny between human and mouse suggests that the sequence on mouse chromosome 19 corresponds to the structural H gene.
Multiple ferritin H subunit sequences are present in the genome of higher vertebrates, but it is not yet known with certainty if more than one is expressed. In this paper, we provide evidence that there is only one functional ferritin H gene in the mouse. We screened a mouse genomic library using a mouse ferritin H cDNA as a probe and characterized five clones. These genomic clones proved to contain three pseudogenes and two allelic forms of a unique functional gene. These two alleles differed by only two point mutations in the promoter and three in the first intron and by a 31-bp insertion in the first intron. They were equally expressed when transiently transfected in HeLa cells. These five genomic clones account for all the bands observed on a Southern blot of mouse genomic DNA hybridized with a ferritin H cDNA, and these bands present a restriction fragment length polymorphism between various representatives of the genus Mus. Using a DNA panel prepared from the backcross progeny (C57BL/6 X Mus spretus)F1 X C57BL/6, we localized the functional ferritin H gene (Fth) in region B of mouse chromosome 19 and established cen-Ly-1-Fth-Pax-2 as the most likely gene order, thus defining a conserved syntenic fragment with human chromosome 11q.
A deficiency in the activity of uroporphyrinogen decarboxylase (URO-D), the fifth enzyme of the haem biosynthetic pathway, is found in two hereditary diseases, familial porphyria cutanea tarda (PCT) and hepatoerythropoietic porphyria (HEP). Little is known about the genetic relationship between those two diseases and it has been postulated that HEP is the homozygous form of PCT. A URO-D cDNA was cloned from an HEP patient and the comparison between the mutant and the wild-type sequences showed a single base difference within the coding sequence leading to the replacement of a glutamic acid by a lysine at codon 167 of the mutant protein. This replacement produced a protein which is rapidly degraded in the presence of cell lysate. On the basis of hybridization of synthetic oligomers to amplified genomic DNA, we demonstrated that this patient is homozygous for this single base mutation. In order to look for any relationship between HEP and PCT, we tested six unrelated patients with familial PCT and could not detect the codon 167 mutation in any of them. These results indicate an heterogeneity in the mutations responsible for the PCT and HEP phenotypes.
Explore the source record for details and available documents.
Four mutations of the porphobilinogen (PBG) deaminase gene that result in cross-reacting immunological material (CRIM)-negative forms of acute intermittent porphyria (AIP) have been identified by in vitro amplification of cDNA from patients and by cloning of the amplified products in a bacterial expression vector. One mutation is a single base deletion which causes a frameshift and which is expected to result in the synthesis of a truncated protein. Two other mutations consist of single base substitutions and lead to amino acid changes. The fourth mutation is a single base substitution producing an aberrant splicing and resulting in an mRNA which would encode a protein missing three amino acids. DNAs from 16 unrelated CRIM-negative AIP patients were screened for the presence of these four mutations, by hybridization with oligonucleotides specific for each of the mutations, but none of the four mutations was identified in additional patients. The results indicate that mutations responsible for CRIM-negative AIP are highly heterogenous.
Porphobilinogen deaminase (PBG-D), the third enzyme in the heme synthetic pathway, possesses two isoforms encoded by distinct mRNAs that are the result of transcription of a single gene from two promoters through differential splicing. During erythroid differentiation, only the expression of the erythroid-specific isoform (E-PBGD) was increased. A system was developed to evaluate genetic expression of E-PBGD in samples limited in cell number and/or mRNA copy. Total RNA from human cells was reverse-transcribed and amplified by the polymerase chain reaction in the same tube with an internal standard that is an in vitro transcript of a cDNA differing from its sample counterpart by a few restriction sites and 24 bp (10%) in the target region. The primers spanned through regions where sample and standard templates were identical in sequence. Amplified templates were resolved by restriction enzyme digestion and gel electrophoresis and quantified by densitometer tracing of corresponding bands on autoradiograms. When an appropriate amount of internal standard is present in the reaction mixture, the ratio of amplified sample versus standard template is proportional to the amount of sample RNA and it is therefore possible to calculate the number of specific mRNA molecules in the original sample.
Congenital erythropoietic porphyria (Günther's disease) is a rare disorder of heme biosynthesis inherited in an autosomal recessive fashion. The molecular abnormality responsible for the characteristic defect in uroporphyrinogen III synthase activity was investigated in two patients. For the first patient, complementary DNA was specifically amplified using the polymerase chain reaction and subsequently cloned and sequenced. Data obtained revealed the coexistence of two distinct point mutations: a T to C change in codon 73 (arginine in place of a cysteine) and a C to T change in codon 53 (leucine in place of a proline). The second case was studied by hybridization with allele specific oligonucleotides and was found to be homozygous for the same mutation in codon 53. These are the first mutations to be recognized in the uroporphyrinogen III synthase gene from congenital erythropoietic porphyria patients.
In 1964 a child with an exceptional form of porphyria was described; she excreted persistently excessive amounts of delta-aminolaevulinic acid, porphobilinogen and uroporphyrin in her urine from early childhood. The biochemical profile resembled that of acute intermittent porphyria (AIP). The child died at the age of 8 years. Reinvestigation of some urine samples by HPLC revealed differences in comparison with urines of other patients with AIP. The clinical picture characterized by porencephaly and severe retardation in development was completely different from that of AIP. Her mother suffered from AIP but the father never had attacks. Investigations on blood and urine samples of the father showed that he also was affected. Due to the early onset in the index patient, its persistent character, and the fact that both parents are affected we postulate retrospectively to have diagnosed a case of homozygous or a double heterozygous AIP, hitherto undescribed.