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J Frézal

Publications and source records attributed to J Frézal.

At least 19 recordsLinked to original sources
PubMed1996

Retinal-specific guanylate cyclase gene mutations in Leber's congenital amaurosis.

Leber's congenital amaurosis (LCA, MIM 204,000), the earliest and most severe form of inherited retinopathy, accounts for at least 5% of all inherited retinal dystrophies. This autosomal recessive condition is usually recognized at birth or during the first months of life in an infant with total blindness or greatly impaired vision, normal fundus and extinguished electroretinogram (ERG). Nystagmus (pendular type) and characteristic eye poking are frequently observed in the first months of life (digito-ocular sign of Franceschetti). Hypermetropia and keratoconus frequently develop in the course of the disease. The observation by Waardenburg of normal children born to affected parents supports the genetic heterogeneity of LCA. Until now, however, little was known about the pathophysiology of the disease, but LCA is usually regarded as the consequence of either impaired development of photoreceptors or extremely early degeneration of cells that have developed normally. We have recently mapped a gene for LCA to chromosome 17p13.1 (LCA1) by homozygosity mapping in consanguineous families of North African origin and provided evidence of genetic heterogeneity in our sample, as LCA1 accounted for 8/15 LCA families in our series. Here, we report two missense mutations (F589S) and two frameshift mutations (nt 460 del C, nt 693 del C) of the retinal guanylate cyclase (RETGC, GDB symbol GUC2D) gene in four unrelated LCA1 probands of North African ancestry and ascribe LCA1 to an impaired production of cGMP in the retina, with permanent closure of cGMP-gated cation channels.

Blindness↗
PubMed1995

[Fifty years of medical genetics. A tribute to Maurice Lamy on the hundredth anniversary of his birth].

Before 1960, no disease gene had been mapped to human chromosome apart from the sex-linked characters which are carried by the X chromosome. The first assignments were inferred from the results of somatic cells hydridization and concerned enzymatic deficiencies and protein defects. They were followed by the data gained from the cytogenetics studies of microrearrangements, either deletions or translocations. The family and linkage studies began to be successfully undertaken following the discovery of polymorphic probes. The breakthrough came out with the availability of highly polymorphic microsatellites scanning quite evenly, the major part of the genome. Currently, more than 1,000 clinical disorders are mapped and compiled in the database GID/GENATLAS. They concern all chapters and extend to characters which are usually sporadic, such as malignant tumours and congenital malformations. The mapping endeavour already had great impact on our understanding of fundamental life processes and unveiled the extent of genetic heterogeneity of diseases. Its major consequences concern prenatal diagnosis. The applications tend to extend towards presymptomatic diagnosis, and screening of carriers, two procedures still controversial, which request due consideration of their inherent risks and side effects and cannot be undertaken without the informed consent of patients. Predictive testing for the detection of liabilities is still a subject of lively debate. Although the spectacular advances of mapping and its implications open great hopes for the prevention and even cure of disease, care has to be taken to their limits and risks and, in their approach, full consideration must be given the respect if human person.

France↗
PubMed1993

[Prenatal, neonatal and postnatal prevention in cystic fibrosis].

The efficiency of neonatal screening for CF could be improved by associating a molecular analysis to the immunoreactive trypsin test, on the same dried blood's sample. However the interest of such a screening for the patients benefit remains controversial. In most cases, antenatal diagnosis may be performed by a direct search of the mutation(s). However, the impact of antenatal diagnosis on CF's incidence will necessarily be limited if it can only be implemented after the birth of an affected child. Hence the interest of screening programs for the detection of healthy carriers. Carrier's detection does not raise any objection for the relatives of patients. It is still premature to recommend it to be undertaken in the general population.

Cystic Fibrosis↗
PubMed1992

[Phenylketonuria yesterday and today. Evaluation of the work of systematic neonatal screening].

Phenylketonuria is due in the very great majority of cases to a deficiency in phenylalanine hydroxylase, an enzyme whose cofactor is biopterin. Prenatal screening consists in measuring the concentration of phenylalanine in a sample of dried blood taken after birth (levels are already raised by day 3). Screening, organized by the Association française pour le dépistage et la prévention des handicaps de l'enfant, is very thorough (cover greater than 99%). Treatment involves observance of dietary restriction for at least five years. Results are good. Questions concerning the useful duration of dietary treatment, the level of phenylalanine that should not be exceeded, and the future of girls with PKU remain controversial. When adult, such girls may give birth to retarded children if they do not resume dietary restriction before becoming pregnant. Now that problems of screening, its organization, and the management of diet have been solved, these questions are the new challenge that faces us.

Female↗
PubMed1992

A gene for Usher syndrome type I (USH1A) maps to chromosome 14q.

Usher syndrome (US) is an autosomal recessive disease characterized by congenital hearing impairment and retinitis pigmentosa. It is the most frequent cause of deaf-blindness in adults and accounts for 3 to 6% of deaf children. Here, we report the genetic mapping of a gene for US type I (USH1A), the most severe form of the disease, to the long arm of chromosome 14, by linkage to probe MLJ14 at the D14S13 locus in 10 families of Western France ancestry (Z = 4.13 at theta = 0). Among them, 8 families originated from a small area of the Poitou-Charentes region (Z = 3.78 at theta = 0), suggesting that a founder effect could be involved. However, since not all US type I families were found to be linked to this locus, the present study provides evidence for genetic heterogeneity of this condition (heterogeneity versus homogeneity test HOMOG, P < 0.05; heterogeneity versus no linkage, P < 0.01).

Chromosome Mapping↗
PubMed1992

Mapping the eye diseases.

In this review the authors first give an overview of the general strategies of mapping which differ whether the biochemical (molecular) defect of the disease is known or not. The main problems besides mapping are concerned for the first category with the correlation between mutation and phenotype and for the second, with heterogeneity, genetic vs phenotypic. Finally, tables are displayed of eye diseases or diseases with eye involvement (metabolic or not) which have been currently mapped, as well as candidate genes actually or putatively involved in visual transduction.

Chromosome Mapping↗
PubMed1991

Spectrum of phenylketonuria mutations in western Europe and north Africa, and their relation to polymorphic DNA haplotypes at the phenylalanine hydroxylase locus.

A total of 252 chromosomes from 126 patients with phenylalanine hydroxylase (PAH) deficiencies were analyzed for both mutant genotypes and restriction fragment length polymorphism (RFLP) haplotypes at the PAH locus. The mutant genes studied originated either from Western Europe (116 alleles) or from Mediterranean countries (136 alleles). Only 27% of all mutant alleles were found to carry identified mutations, particularly mutations at codon 252 (2.3%), 261 (7.5%), 280 (6.3%), 408 (3.5%) and at the splice donor site of intron 12 (6.3%). The mutant genotypes were associated with RFLP haplotypes 7, 1, 38, 2 and 3 at the PAH locus respectively. Except for the splice mutation of intron 12, these associations were preferential, but not exclusive, since the other four mutations were found on the background of at least two RFLP haplotypes. These results, together with the observation that 85% of PAH deficient patients are heterozygotes for their mutant genotypes, emphasize the great heterogeneity of PAH deficiencies in Mediterranean countries and hamper systematic DNA testing for carrier status in this population.

Africa, Northern↗
PubMed1991

In situ hybridization of two markers closely flanking the spinal muscular atrophy gene to 5q12----q13.3.

In order to refine the physical location of the p105-153Ra and M4 probes which closely flank the spinal muscular atrophy gene (SMA) on human chromosome 5q, in situ hybridization has been carried out on prometaphase chromosomes. Our results demonstrate that the disease gene is located between the 5q12----q13.1 and 5q13.3 bands. The present study will hopefully contribute to microdissection of the chromosomal region of the SMA gene.

Child↗
PubMed1991

Linkage analysis in spinal muscular atrophy, by six closely flanking markers on chromosome 5.

The proximal spinal muscular atrophies (SMA) represent the second most common autosomal recessive disorder, after cystic fibrosis. The gene responsible for chronic SMA has recently been mapped to chromosome 5q by using genetic linkage studies. Among six markers mapping to this region, five were shown to be linked with the SMA locus in 39 chronic SMA families each containing at least two affected individuals. Multilocus analysis by the method of location score was used to establish the best estimate of the SMA gene location. Our data suggest that the most likely location for SMA is between loci D5S6 and D5S39. The genetic distances between these two markers are estimated to be 6.4 cM in males and 11.9 cM in females. Since meiosis were informative with D5S39 and D5S6 in 92% and 87% of SMA families, respectively, it is hoped that the present study will contribute to the calculation of genetic risk in SMA families.

Chromosome Mapping↗
PubMed1990

[Cystic fibrosis: a gene at the end of the road].

The authors first give an account of the work undertaken jointly by two Canadian and one American groups, which lead to the cloning and identification of the cystic fibrosis gene. To achieve this aim, it was necessary to clone a large region amounting to 500 kb, using chromosome walking and jumping. The gene was located from a cross-hybridization signal with two probes from the cloned region and bovine cDNA. The CF gene is made of 24 exons giving a messenger of 6,500 nucleotides and a protein of about 1,500 aminoacids. The protein structure has been deduced from its composition in aminoacids. However, the localization of the protein in the cell and its true function remain an open question. At the same time workers from those groups identified the prevalent mutation in CF. These outstanding achievements will help unravelling the physiopathology of the disease. They increase the possibilities of prevention, but it is fanciful to think that they can lead to its eradication.

Chromosome Mapping↗
PubMed1990

OFDI syndrome.

Explore the source record for details and available documents.

Humans↗
PubMed1990

Clinical and genetic heterogeneity in retinitis pigmentosa.

The clinical course of defective vision and blindness has been investigated in relation to different modes of genetic transmission in a large series of 93 families with retinitis pigmentosa (RP). For autosomal dominant RP, two clinical subtypes could be distinguished according to the delay in macular involvement. In the severe form, macular involvement occurred within 10 years, while in the mild form, macular involvement occurred after 20 years. Interestingly, a significant increase of mean paternal age (38.8 years, mean controls in France = 29.1 years, P less than 0.001) was found in this form of RP, a feature which is suggestive of new mutations. For autosomal recessive RP, four significantly different clinical subtypes could be recognized, according to both age of onset and the pattern of development (P less than 0.001), namely cone-rod dystrophy and early-onset severe forms on the one hand (mean age of onset = 7.6 years), late-onset mild forms and senile forms on the other. Similarly, two significantly different clinical subtypes could be recognized in X-linked RP, according to both mode and age of onset, which were either myopia (mean age = 3.5 +/- 0.5 years) or night blindness (mean age = 10.6 +/- 4.1 years. P less than 0.001). By contrast, no difference was noted regarding the clinical course of the disease, which was remarkably severe whatever the clinical subtype (blindness before 25 years). In addition, all obligate carriers in our series were found to have either severe myopia or pigment deposits in their peripheral retina. Finally, sporadic RP represented the majority of cases in our series (42%). There was a considerable heterogeneity in this group, and at least three clinical forms could be recognized, namely cone-rod dystrophy, early onset-severe forms and late onset moderate forms. At the beginning of the disease, the hereditary nature of the sporadic forms was very difficult to ascertain (especially between 7-10 years) and only the clinical course could possibly provide information regarding the mode of inheritance. However, the high level of consanguinity, and the high sex ratio in early onset and severe sporadic forms (including cone-rod dystrophy), was suggestive of an autosomal or X-linked recessive inheritance, while increased paternal age in late onset forms was suggestive of autosomal dominant mutations.

Adolescent↗
PubMed1990

Assignment of human tracheobronchial mucin gene(s) to 11p15 and a tracheobronchial mucin-related sequence to chromosome 13.

Extensive heterogeneity of tracheobronchial mucin RNAs has been described recently. Based on the results of total or partial cDNA sequencing, the mucin cDNAs obtained were classified into three groups. The first group contained 24 bp tandem repeat sequences, the second exhibited homology at their amino- and carboxyl-terminals, and the third group seems to consist of alternative hydrophilic-hydrophobic zones. JER58, JER47 and JER57 probes, representing the first, second, and third tracheobronchial mucin families respectively, were used for chromosome assignment. In human DNAs digested with BamHI, the JER58 probe detected a sequence of 21 kb, the JER47 probe detected a major sequence of 21 kb and a minor sequence of 4 kb, and the JER57 probe detected two sequences of 1.8 kb and 1.3 kb. By somatic hybrid cell analysis, the JER58. JER47, and JER57 major sequences were assigned to chromosome 11 and the JER47 minor sequence to chromosome 13. By in situ hybridization the JER58, JER47 and JER57 probes were assigned to 11p15. Under the experimental conditions used, no specific hybridization to the chromosome 13 region was observed with the JER47 probe. Our results indicate that tracheobronchial mucin gene(s) is/are localized on 11p15. The minor JER47 BamHI sequence localized on chromosome 13 probably corresponds to a tracheal-mucin related sequence. The intestinal mucin gene was also recently localized to the same 11p15 region. Intestinal and tracheobronchial mucins appear different according to their tissue distribution and their cDNA nucleotide sequences. Tracheal mucin probes (JER58, JER47, JER57) and intestinal probes may represent independent genes on 11p15 or else different mRNAs from the same primary transcript produced by differential splicing. Further studies using mucin genomic probes for 11p15 will be required for the elucidation of tracheal and intestinal mucin gene organisation in this region.

Animals↗