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Biomedical subjects

E Mornet

Publications and source records attributed to E Mornet.

At least 19 recordsLinked to original sources
PubMed1995

Screening of CYP21 gene mutations in 129 French patients affected by steroid 21-hydroxylase deficiency.

The frequency of 12 different mutations of the steroid 21-hydroxylase gene (CYP21) was investigated in 129 French patients affected by congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency. Eighty-nine percent of the CAH chromosomes were characterized. The most frequent mutations were a C-G substitution in intron 2, the deletion of the CYP21 gene and a T-A substitution in exon 4 in the severe form of the disease, and a G-T substitution in exon 7 in the nonclassic form. The correlation between the genotypes and the clinical forms of the disease showed marked variation in the phenotype from a single genotype, suggesting that individual variation and undetected additional mutations on the same CAH chromosome accounted for the phenotype. In 65 informative meioses of CAH families, no de novo mutation was found.

Adrenal Hyperplasia, Congenital↗
PubMed1994

Identification by molecular diagnosis of mosaic Turner's syndrome in an obligate carrier female for fragile X syndrome.

A case of mosaic Turner's syndrome with a 45,X/46,XX/47,XXX karyotype, who was also a fragile X obligate carrier as the mother of an affected boy, was identified by molecular diagnosis. Complete haplotyping and direct DNA analysis showed that the X chromosome in all metaphases was the normal X. At the age of 57, she is mentally normal. Her external appearance was typical of Turner's syndrome. This report shows that molecular studies in conjunction with cytogenetic analysis can help in the clinical diagnosis of a rare case and can show the uniqueness of a case such as the one here described.

Female↗
PubMed1994

A multicenter study on genotype-phenotype correlations in the fragile X syndrome, using direct diagnosis with probe StB12.3: the first 2,253 cases.

We report the results of a 14-center collaborative study of genotype-phenotype correlations in 318 fragile X families; these families comprised 2,253 individuals, 1,344 of whom carried a fragile X mutation and 693 of whom had a typical full fragile X mutation. This study demonstrates that direct DNA diagnosis establishes the genotype at the FRAXA-FMR-1 locus. There was a significantly higher prevalence of "mosaic" cases among males who carry a full mutation (12%) than among females who carry a full mutation (6%); the mosaic males had a larger expansion than did the mosaic females. Mental status of premutated individuals did not differ from that of those with a normal genotype. Both the abnormal methylation of the FMR-1-EagI site and the size of the expansion were highly correlated with cytogenetics, facial dysmorphism, macroorchidism, and mental retardation (MR). Among female carriers of a full mutation, those with MR had significantly larger expansion than did those without MR. Among 164 independent couples, 3 unrelated husbands carried a premutation that suggests that the prevalence of fragile X premutations in the general population is approximately 0.9% of the X chromosomes. Our data validate the use of direct DNA testing for fragile X diagnosis as well as for carrier identification and support and complete the established relationships among the DNA results and the cytogenetic, physical, and psychological aspects of the disease.

Adolescent↗
PubMed1993

Molecular analysis of a ring chromosome X in a family with fragile X syndrome.

The phenotypically normal sister of a patient affected by fragile X syndrome was referred for genetic counselling and was found to carry a mosaic karyotype 46,X,r(X)/45,X. Because the probability of the simultaneous chance occurrence of fragile X syndrome and a ring chromosome X in the same family is very low, we postulated that the breakpoint of the ring chromosome X originated in the cytogenetic break in Xq27.3 responsible for fragile X syndrome. In order to determine the relative positions of the breakpoint on the ring chromosome X and the (CGG)n unstable sequence responsible for the fragile X mutation, we used molecular markers to analyse the telomeric regions of chromosome X in this family. The results showed that the ring chromosome X was the maternal fragile X chromosome and that the telomeric deletion on the long arm encompassed the (CGG)n sequence. This suggests that the cytogenetic break in Xq27.3 is distinct from the unstable (CGG)n sequence, or that the break followed by the end-to-end fusion creating the ring chromosome was not completely conservative. Analysis of DNA markers on the short arm of chromosome X evidenced a deletion of a large part of the pseudoautosomal region, allowing us to position the genes involved in stature and in some syndromes associated with telomeric deletions of Xp on the proximal side of the pseudoautosomal region.

Adult↗
PubMed1993

General cystic fibrosis mutations are usually missense mutations affecting two specific protein domains and associated with a specific RFLP marker haplotype.

Some 250 different mutations have so far been screened in the cystic fibrosis (CF) gene. The 50 nonsense, 33 splicing and 60 frameshift mutations are randomly distributed within the gene, unlike the 107 missense mutations or amino acid deletions. A large excess of missense mutations affects the exons encoding the first transmembrane (MS1) and first ATP-binding fold (NBF1) domains. Sixty-four of the 107 missense mutations may be classified as private, demic, local and general mutations on the basis of their geographic distribution in Europe. Private and demic mutations are randomly distributed within the gene; local and general mutations are not. It is well known that some RFLP markers are in linkage disequilibrium with some mutations. Private, demic and local mutations are randomly associated with each class of RFLP haplotypes. In contrast, general mutations, frequent and infrequent, are not randomly associated with RFLP markers. General mutations usually affect a specific part of the gene and are more likely to be associated with a specific RFLP marker. This suggests the existence of selective factors favoring these mutations, a hypothesis formerly postulated as a possible cause of the high frequency of the disease.

Cystic Fibrosis↗
PubMed1993

Linkage disequilibrium between the fragile X mutation and two closely linked CA repeats suggests that fragile X chromosomes are derived from a small number of founder chromosomes.

In order to investigate the origin of mutations responsible for the fragile X syndrome, two polymorphic CA repeats, one at 10 kb (FRAXAC2) and the other at 150 kb (DXS548) from the mutation target, were analyzed in normal and fragile X chromosomes. Contrary to observations made in myotonic dystrophy, fragile X mutations were not strongly associated with a single allele at the marker loci. However, significant differences in allelic and haplotypic distributions were observed between normal and fragile X chromosomes, indicating that a limited number of primary events may have been at the origin of most present-day fragile X chromosomes in Caucasian populations. We propose a putative scheme with six founder chromosomes from which most of the observed fragile X-linked haplotypes can be derived directly or by a single event at one of the marker loci, either a change of one repeat unit or a recombination between DXS548 and the mutation target. Such founder chromosomes may have carried a number of CGG repeats in an upper-normal range, from which recurrent multistep expansion mutations have arisen.

Alleles↗
PubMed1992

Carrier detection and prenatal diagnosis of cystic fibrosis using an intragenic TA-repeat polymorphism.

We have analysed the segregation of a TA-repeat polymorphism in intron 17b of the cystic fibrosis transmembrane conductance regulator gene responsible for cystic fibrosis (CF) in 23 French CF families non-informative for the delta F508 mutation (i.e. with at least one parent not carrying delta F508) or closely linked DNA markers. At least 13 different alleles ranging from 7 to 45 repeats were observed and the detected heterozygosity was 89%. Of the 23 families studied, 19 were fully informative for prenatal diagnosis or carrier detection, 3 were partially informative and one was not informative. In 6 families, prenatal diagnosis for CF or carrier detection in siblings of CF cases were performed using this polymorphism.

Base Sequence↗
PubMed1991

Functional insertion of the SV40 large T oncogene in cystic fibrosis intestinal epithelium. Characterization of CFI-3 cells.

Intestinal epithelial cells were isolated from a fetus with cystic fibrosis (CF) and transfected with a plasmid vector recombined with the ori- mutant of SV40. A population of proliferative cells was then subcloned and designated as CFI-3. These cells had a doubling time of 24 h and were maintained in culture for up to 25 passages. At passage 8, CFI-3 cells did not produce any tumors in nude mice. Northern blot and immunofluorescence studies indicated that the extended lifespan of CFI-3 cells results in genomic insertion of SV40 LT. Intestinal CFI-3 cells are epithelial, according to the expression of the human cytokeratin 18 gene and poorly differentiated by phase-contrast and electron microscopy. Functional membrane receptors activated by vasoactive intestinal peptide (VIP), its natural analogue pituitary adenylate cyclase activating peptide (PACAP-38), and isoproterenol were observed in CFI-3 cells. Restriction fragment length polymorphism analysis of the PstI KM19 site revealed that the cftr locus was identical in the chorionic villi and in CFI-3 cells. The manifestation of CF in this family was not related to the common mutation delta F508, since this fetus was heterozygous for the substitutions S549N and N1303K. Chloride transport, assessed by the 125I efflux, was induced in CFI-3 cells by the calcium inophore ionomycin, but not by the adenylate cyclase activator forskolin, and was inhibited by the chloride channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid. These results were confirmed in patch clamp studies in which the cpt cAMP analogue failed to stimulate membrane currents, while the calcium ionophore ionomycin stimulated inward currents. We conclude that intestinal CFI-3 cells retain the CF phenotype relating to defective regulation of Cl- channels, and therefore constitute a suitable model, 1) for elucidating the function of CFTR protein, 2) developing new therapeutic agents, and 3) correcting the CF defect by gene replacement therapy in vitro.

Antigens, Polyomavirus Transforming↗
PubMed1991

Nearly 80% of cystic fibrosis heterozygotes and 64% of couples at risk may be detected through a unique screening of four mutations by ASO reverse dot blot.

A technique allowing the simultaneous screening of the four main CF mutations in the French population (delta F508, delta I507, G542X, S549N) has been developed by means of allele sequence-specific oligonucleotide (ASO) reverse dot blot. Using a strategy proposed by R. K. Saïki et al. (1989, Proc. Natl. Acad. Sci. USA 86: 6230-6234) for HLA-DQA, the seven ASOs for normal and mutant CF alleles were given a homopolymer T tail with terminal deoxyribonucleotidyltransferase and then immobilized on a nylon membrane. T-tail homopolymers were preferentially bound to the nylon, leaving the specific ASO sequences free to hybridize with amplified and radiolabeled exons 10 and 11 of a patient. These exons were simultaneously coamplified by a multiplex PCR and radiolabeled by random priming. ASO reverse dot blot currently appears to be the most efficient, rapid, and economic means of screening the population for CF mutations. This screening can detect nearly 80% of carriers and 64% of couples at risk and could prevent the birth of CF-affected infants in these families.

Alleles↗
PubMed1991

Nine mutations in the cystic fibrosis (CF) gene account for 80% of the CF chromosomes in French patients.

Thirteen mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been screened in a French sample of 185 cystic fibrosis (CF) patients, together with their respective associated RFLP haplotypes at the linked D7S23 locus (XV2C and KM19 markers). The respective frequencies of the mutations showed that 9 of them account for 80% of the CF chromosomes. Implications for prenatal diagnosis and heterozygote detection are defined and discussed. The well-known great excess of RFLP B marker within CF chromosomes is partially explained by two already characterized mutations highly associated with haplotype B: delta F508 and G542X. Similarly, the excess of haplotype D within CF chromosomes is partially explained by the association between delta I507 and this haplotype. These results may suggest the existence of two still untested or uncharacterized mutations, whose frequencies could be near 1%, one which would be associated with haplotype B and a second which would be associated with haplotype D. The possible cause of the specific association between most of the main different CF mutations and the RFLP haplotype B is discussed.

Alleles↗
PubMed1991

Distribution of deletions and seven point mutations on CYP21B genes in three clinical forms of steroid 21-hydroxylase deficiency.

To characterize mutations in the CYP21B gene that are responsible for congenital adrenal hyperplasia (CAH), DNA samples from 91 French patients have been studied by allelic-specific oligonucleotide hybridization and Southern blot analysis. Seven sites mostly found in the CYP21A pseudogene and deletions of the functional CYP21B gene have been screened. Gene conversions involving small DNA segments accounted for 57% of the tested mutations and probably cause 74% of the mutations responsible for the disease. Complete deletion of the CYP21B gene accounted for 18% of the CAH mutations in the whole sample and for 21% in the classical form of the disease. Three mutations were found associated with specific clinical forms of the disease: a G-C substitution in the seventh exon was associated with the late-onset form of the disease, and both an 8-bp depletion in the third exon and complete deletion of CYP21B were associated with the salt-wasting form.

Adrenal Hyperplasia, Congenital↗
PubMed1990

Studies of RFLP closely linked to the cystic fibrosis locus throughout Europe lead to new considerations in populations genetics.

The prenatal diagnosis of cystic fibrosis is now routinely performed by using two probes tightly linked to the CF locus (XV2C and KM19). These probes have been shown to exhibit a strong linkage disequilibrium with the CF locus. Our data (103 families) have been pooled with other French data (237 families). They are consistent with the hypothesis of a unique ancestral mutation initially associated with a B (D1E2) restriction fragment length polymorphism (RFLP) haplotype, subsequently reassociated by cross-over with A, C or D haplotypes. Assuming such an hypothesis, the mutation is supposed to be 3000-6000 years old, depending on generation length and the true recombination ratio between the KM19 and CF loci. Up-to-date Spanish, Danish and Greek data are reported together with other previously published population data in order to discuss the geographic origin and age of the mutation in Europe. The action of selection in terms of heterozygote advantage and distorsion of segregation is discussed.

Cystic Fibrosis↗
PubMed1990

The cystic fibrosis delta F508 mutation in the French population.

French families (n = 129) with at least one cystic fibrosis (CF) affected child and 44 unrelated subjects from the general population were tested for the presence of the delta F508 mutation by the polymerase chain reaction. The delta F508/CF mutation ratio (CF: uncharacterised CF mutations) was tested in the CF families with and without meconium ileus. The association between delta F508 and CF mutations and restriction fragment length polymorphism haplotypes (XV2c and KM19) has been estimated; these data suggest that the CF chromosomes include a panel of independent and probably different mutations.

Cystic Fibrosis↗