Showing papers by "Jean-Louis Mandel published in 1993"

Putative X-linked adrenoleukodystrophy gene shares unexpected homology with ABC transporters

Abstract: Adrenoleukodystrophy (ALD) is an X-linked disease affecting 1/20,000 males either as cerebral ALD in childhood or as adrenomyeloneuropathy (AMN) in adults. Childhood ALD is the more severe form, with onset of neurological symptoms between 5-12 years of age. Central nervous system demyelination progresses rapidly and death occurs within a few years. AMN is a milder form of the disease with onset at 15-30 years of age and a more progressive course. Adrenal insufficiency (Addison's disease) may remain the only clinical manifestation of ALD. The principal biochemical abnormality of ALD is the accumulation of very-long-chain fatty acids (VLCFA) because of impaired beta-oxidation in peroxisomes. The normal oxidation of VLCFA-CoA in patients' fibroblasts suggested that the gene coding for the VLCFA-CoA synthetase could be a candidate gene for ALD. Here we use positional cloning to identify a gene partially deleted in 6 of 85 independent patients with ALD. In familial cases, the deletions segregated with the disease. An identical deletion was detected in two brothers presenting with different clinical ALD phenotypes. Candidate exons were identified by computer analysis of genomic sequences and used to isolate complementary DNAs by exon connection and screening of cDNA libraries. The deduced protein sequence shows significant sequence identity to a peroxisomal membrane protein of M(r) 70K that is involved in peroxisome biogenesis and belongs to the 'ATP-binding cassette' superfamily of transporters.

The FMR-1 protein is cytoplasmic, most abundant in neurons and appears normal in carriers of a fragile X premutation.

Abstract: Fragile X mental retardation syndrome is caused by the unstable expansion of a CGG repeat in the FMR–1 gene. In patients with a full mutation, abnormal methylation results in suppression of FMR–1 transcription. FMR–1 is expressed in many tissues but its function is unknown. We have raised monoclonal antibodies specific for the FMR–1 protein. They detect 4–5 protein bands which appear identical in cells of normal males and of males carrying a premutation, but are absent in affected males with a full mutation. Immunohistochemistry shows a cytoplasmic localization of FMR–1. The highest levels were observed in neurons, while glial cells contain very low levels. In epithelial tissues, levels of FMR–1 were higher in dividing layers. In adult testis, FMR–1 was detected only in spermatogonia. FMR–1 was not detected in dermis and cardiac muscle except under pathological conditions.

Origin of the expansion mutation in myotonic dystrophy.

Abstract: Myotonic dystrophy (DM) is caused by the expansion of a CTG trinucleotide repeat. The mutation is in complete linkage disequilibrium with a nearby two–allele insertion/deletion polymorphism, suggesting a single origin for the mutation or predisposing mutation. To trace this ancestral event, we have studied the association of CTG repeat alleles in a normal population to alleles of the insertion/deletion polymorphism and of a (CA)n repeat marker 90 kilobases from the DM mutation. The results strongly suggest that the initial predisposing event(s) consisted of a transition from a (CTG)5 allele to anallele with 19 to 30 repeats. The heterogeneous class of (CTG)19–30 alleles which has an overall frequency of about 10%, may constitute a reservoir for recurrent DM mutations.

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.

Abstract: 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 fragil X chromosomes. Contrary to observations made in myotonic dystrophy, fragil 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. The authors 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. 23 refs., 2 figs., 3 tabs.

Friedreich's ataxia phenotype not linked to chromosome 9 and associated with selective autosomal recessive vitamin E deficiency in two inbred Tunisian families

Abstract: Friedreich9s ataxia (FA) is an autosomal recessive neurodegenerative disorder, the disease locus (FRDA) of which has been assigned to 9q13-q21.1 by genetic linkage analysis in affected families. We report two large inbred Tunisian families with FA manifestations that did not show the expected linkage. The disease locus could be excluded from a large (12 cMO) region around FRDA. This is the first report providing evidence for nonallelic genetic heterogeneity for the FA clinical phenotype. On subsequent analysis, all patients had very low levels of serum vitamin E whereas the parents and healthy sibs had normal vitamin E levels. This establishes that the selective vitamin E deficiency with normal fat absorption is an autosomal recessive trait, which is associated in the two families reported here with the FA phenotype.

Gene in the region of the Friedreich ataxia locus encodes a putative transmembrane protein expressed in the nervous system.

Abstract: Friedreich ataxia (FRDA) is an autosomal recessive degenerative disorder that affects the cerebellum, spinal cord, and peripheral nerves. The FRDA gene was localized in 9q13-q21 within 0.7 centimorgan of the D9S5 and D9S15 loci. One recently reported recombination event and haplotype analysis in a population with a founder effect suggested that the FRDA locus is on the D9S5 side. Using a conserved probe from the D9S5 locus, we have now identified an approximately 7-kilobase (kb) transcript and report cloning of its cDNA. The corresponding gene, X11, extends at least 80 kb in a direction opposite D9S15. The gene is expressed in the brain, including the cerebellum, but is not detectable in several nonneuronal tissues and cell lines. In situ hybridization of adult mouse brain sections showed prominant expression in the granular layer of the cerebellum. Expression was also found in the spinal cord. The cDNA contains an open reading frame encoding a 708-amino acid sequence that shows no significant similarity to other known proteins but contains a unique, 24-residue-long, putative transmembrane segment. On the basis of its genomic localization and its neuronal site of expression, particularly in the cerebellum, this "pioneer" gene represents a candidate for FRDA. Direct evidence of its involvement in FRDA will require a search for causative point mutations in patients.

Striking founder effect for the fragile X syndrome in Finland.

Abstract: The fragile X mental retardation syndrome is caused by the expansion of an unstable CGG repeat in a 5' exon of the FMR1 gene. Significant linkage disequilibrium between this mutation and flanking microsatellite markers has been observed previously in Caucasian populations, a very unusual finding for an X-linked disease which severely impairs reproduction fitness in affected males. This reflects the multistep process at the origin of the full mutation. We have analyzed the FRAXAC2 and DXS548 microsatellites in 26 fragile X families originating from various parts of Finland, and report a striking founder effect much stronger than the linkage disequilibrium observed previously in other more heterogeneous populations. One DXS548 allele was present on 92% of fragile X chromosomes and on 17% of normal chromosomes. A single haplotype accounted for 73% of fragile X chromosomes, and was found only once in 34 normal chromosomes, corresponding to a relative risk of about 90 compared to its absence. The broad geographic origin of the high-risk haplotype and its expected frequency suggest that it was present in initial settlers of Finland, and could thus have been carried silently through 100 generations.

Abnormal messenger RNA expression and a missense mutation in patients with X-linked adrenoleukodystrophy

Abstract: A candidate gene for X-linked adrenoleukodystrophy (ALD) has been identified via positional cloning strategies. We now report messenger RNA expression in fibroblasts from 6 unrelated ALD patients. Four patients lacked the normal 4.2 kb transcript, three of them having deletions of the ALD gene. A fifth patient with a deletion of 1.6 kb had a smaller 4.0 kb transcript. The last patient had a normal sized transcript and a missense mutation at base 1258 leading to Glu-291-Lys substitution in a region of the candidate gene protein which is conserved in the 70 kD peroxisomal membrane protein. These results provide further evidence that this candidate gene is indeed the ALD gene.

Genetic recombination events which position the Friedreich ataxia locus proximal to the D9S15/D9S5 linkage group on chromosome 9q.

Abstract: The absence of recombination between the mutation causing Friedreich ataxia and the two loci which originally assigned the disease locus to chromosome 9 has slowed attempts to isolate and characterize the genetic defect underlying this neurodegenerative disorder. A proximity of less than 1 cM to the linkage group has been proved by the generation of high maximal lod score (Z) to each of the two tightly linked markers D9S15 (Z = 96.69; recombination fraction [theta] = .01) and D9S5 (Z = 98.22; theta = .01). We report here recombination events which indicate that the FRDA locus is located centromeric to the D9S15/D9S5 linkage group, with the most probable order being cen-FRDA-D9S5-D9S15-qter. However, orientation of the markers with respect to the centromere, critical to the positional cloning strategy, remains to be resolved definitively.

Linkage Disequilibrium Analysis of Friedreich’s Ataxia in 140 Caucasian Families: Positioning of the Disease Locus and Evaluation of Allelic Heterogeneity

Abstract: We investigated linkage disequilibrium between Friedreich's ataxia (FRDA) and four tightly linked multi-allele markers in 140 families from France and Italy. These markers include three microsatellites (D9S111, D9S15 and D9S110) and one RFLP (D9S5). Their chromosomal order, D9S111-D9S15-D9S110-D9S5, had previously been established by physical mapping. Linkage disequilibrium was evaluated between each marker and FRDA and between markers. Extended haplotypes were obtained and their frequencies on FRDA and normal chromosomes were evaluated. We obtained evidence of strong allelic association of FRDA with D9S5 only. Analysis of linkage disequilibrium between markers revealed a significant decrease between D9S110 and D9S5, suggesting the presence of a recombination hot spot in the interval between these markers. Probably for this reason, no major FRDA-associated extended haplotype could be identified. Our data suggest the presence of a few common disease-causing mutations in the examined population, and indicate a putative localization for the FRDA gene. Transcribed sequences have been found in this candidate region.

X-linked adrenoleukodystrophy gene and corresponding protein

Abstract: The present invention relates to adrenoleukodystrophy proteins and uses thereof. More particularly, the invention relates to human adrenoleukodystrophy proteins. Mutations of the adrenoleukodystrophy protein cause adrenoleukodystrophy or adrenomyelopathy.

Microsatellites and disease: A new paradigm

Abstract: Disease-causing mutations are generally stable within the span of a few generations during which we can follow them by DNA analyses. This is not true for three diseases, uncovered during a span of less than a year, which are caused by mutations in microsatellites, by trinucleotide repeat expansions. These mutations are unstable. They vary between different members in a kindred, between sibs, and even between tissues and cells of the same individual. This new type of unstable or dynamic mutation is responsible for the fragile X syndrome, myotonic dystrophy and X-linked spinal and bulbar muscular atrophy (SBMA) also called Kennedy disease. While at the root of these diseases, variable triplet repeat expansion also offers an explanation for some unusual genetic features of at least two of these diseases, the phenomenon of anticipation and that of variable expression and incomplete penetrance. Several recent reviews and editorials have discussed the unusual features and characteristics of this new type of mutation (Mandel and Heitz, 1992; Caskey et al., 1992; Rousseau et al., 1992a; Richards and Sutherland, 1992; Rousseau et al., 1992b; Harper et al., 1992; Sutherland and Richards, 1992).

DNA sequences related to fragile X syndrome

Abstract: The DNA sequence spanning the fragile X site on the X human chromosome has been obtained in purified and isolated form. As fragile X is associated with mental retardation, the availability of a DNA which spans this locus permits diagnosis and treatment of the related mental disorders.