Showing papers by "Guy A. Rouleau published in 1995"

Correlation between CAG repeat length and clinical features in Machado-Joseph disease

Abstract: Machado-Joseph disease (MJD) is associated with the expansion of a CAG trinucleotide repeat in a novel gene on 14q32.1. We confirmed the presence of this expansion in 156 MJD patients from 33 families of different geographic origins: 15 Portuguese Azorean, 2 Brazilian, and 16 North American of Portuguese Azorean descent. Normal chromosomes contain between 12 and 37 CAG repeats in the MJD gene, whereas MJD gene carriers have alleles within the expanded range of 62-84 CAG units. The distribution of expanded alleles and the gap between normal and expanded allele sizes is either inconsistent with a premutation hypothesis or most (if not all) of the alleles we studied descend from a common ancestor. There is a strong correlation between the expanded repeat size and the age at onset of the disease as well as the clinical presentation. There is mild instability of the CAG tract length with transmission of the expanded alleles; both increase and decrease in size between parents and progeny occur, with larger variations in male than in female transmissions. Together, these effects can partly explain the variability of age at onset and of phenotypic features in MJD; however, other modifying factors must exist.

The oculopharyngeal muscular dystrophy locus maps to the region of the cardiac α and β myosin heavy chain genes on chromosome 14q11.2−q13

Abstract: Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant muscular dystrophy which presents typically after the age of 50 with progressive eyelid drooping and an increasing difficulty in swallowing. Though OPMD has a world-wide incidence, it is more common in the French Canadian population. We have identified a homogeneous group of families and studied 166 polymorphic markers as part of a genome search before establishing linkage to chromosome 14. We determined that the OPMD locus maps to a less than 5 cM region of chromosome 14q11.2-q13. The maximum two-point lod score in three French Canadian families of 14.73 (theta = 0.03) was obtained for an intronic cardiac beta myosin heavy chain gene (MYH7) marker. The regional localization for the OPMD locus raises the intriguing possibility that either the cardiac alpha or beta myosin heavy chain genes may play a role in this disease.

Screening for germ-line mutations in the NF2 gene.

Abstract: Neurofibromatosis type 2 (NF2) is a monogenic dominantly inherited disease that predisposes to the development of tumors of the nervous system, particularly meningiomas and schwannomas. The gene which, when altered, causes NF2, is localized on chromosome 22 and has recently been identified. The NF2 gene is also the site of somatic mutation in tumors, suggesting that it might have a tumor suppressor activity. We here report a screening method for the detection of point mutations in NF2 which takes advantage of denaturing gradient gel electrophoresis (DGGE). This method efficiently screens 95% of the coding sequence and 90% of intron/exon junctions. When applied to 91 unrelated NF2 patients, it enabled the identification of 32 germ-line mutations. Since mutations are found in only one third of the patients, it is expected that mutations or deletions affecting the promoter and/or intronic regions of the NF2 gene occur frequently. The characterized mutations are preferentially located within the 5' half of the gene. Most of them are predicted to lead to the synthesis of a truncated protein. A search for genotype/phenotype correlations showed that, at least in this series of patients, mild manifestations of the disease were associated with mutations which preserve the C-terminal end of the protein.

The neurofibromatosis type 2 gene product, schwannomin, suppresses growth of NIH 3T3 cells.

Abstract: Cancer is a multistep process that involves the activation of oncogenes and the inactivation of antioncogenes. Recently, a new putative tumor suppressor, the neurofibromatosis type 2 ( NF2 ) gene, was mapped to chromosome 22, cloned, and found to encode for a new protein, merlin/schwannomin, a member of the band 4.1 family of proteins. Members of this family have not been implicated previously in tumorigenesis. They possess significant homology in their NH 2 -terminal domain, which is thought to be important in the binding of the plasma membrane to the underlying actin cytoskeleton. To determine whether schwannomin may affect cell growth, we transfected NIH 3T3 cells with the wild type and an NF2 cDNA lacking 111 amino acids at the NH 2 terminus. We observed slowing of growth and changes in cellular morphology only in cells expressing the wild-type NF2 cDNA. This finding suggests that schwannomin can suppress growth directly and confirms its role in tumor suppression. This system will provide a useful assay to identify important functional domains of the protein.

Cloning of a balanced translocation breakpoint in the DiGeorge syndrome critical region and isolation of a novel potential adhesion receptor gene in its vicinity

Abstract: Deletions of the 22q11.2 have been associated with a wide range of developmental defects (notably DiGeorge syndrome, velocardiofacial syndrome, conotruncal anomaly face syndrome and isolated conotruncal cardiac defects) classified under the acronym CATCH 22. A DiGeorge syndrome patient bearing a balanced translocation whose breakpoint maps within the critical region has been previously described. We report the construction of a cosmid contig spanning the translocation breakpoint and the isolation of a gene mapping 10 kb telomeric to the breakpoint. This gene encodes a novel putative adhesion receptor protein, which could play a role in neural crest cells migration, a process which has been proposed to be altered in DiGeorge syndrome.

Machado Joseph disease maps to the same region of chromosome 14 as the spinocerebellar ataxia type 3 locus.

Abstract: Machado Joseph disease (MJD) is an autosomal dominantly inherited neuro-degenerative disorder primarily affecting the motor system. It can be divided into three phenotypes based on the variable combination of a range of clinical symptoms including pyramidal and extra-pyramidal features, cerebellar deficits, and distal muscle atrophy. MJD is thought to be caused by mutation of a single gene which has recently been mapped, using genetic linkage analysis, to a 29 cM region on chromosome 14q24.3-q32 in five Japanese families. A second disorder, spinocerebellar ataxia type 3 (SCA3), which has clinical symptoms similar to MJD, has also been linked to the same region of chromosome 14q in two French families. In order to narrow down the region of chromosome 14 which contains the MJD locus and to determine if this region overlaps with the predisposing locus for SCA3, we have performed genetic linkage analysis in seven MJD families, six of Portuguese/Azorean origin and one of Brazilian origin, using nine microsatellite markers mapped to 14q24.3-q32. Our results localise the MJD locus in these families to an 11 cM interval flanked by the markers D14S68 and AFM343vf1. In addition we show that this 11 cM interval maps within the 15 cM interval containing the SCA3 locus, suggesting that these diseases are allelic.

Excess of deletions of maternal origin in the DiGeorge/Velo-cardio-facial syndromes. A study of 22 new patients and review of the literature

Abstract: We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a χ2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin.

Absence of mutations in superoxide dismutase and catalase genes in patients with Parkinson's disease

Abstract: Background: Parkinson's disease (PD) is an adultonset, neurodegenerative disorder characterized by a selective loss of the dopaminergic cells of the substantia nigra and by progressive motor decline. Studies have shown aberrant oxidative stress metabolism within the substantia nigra and other dopaminergic regions of the brain in patients with PD. Objective: To screen the genes of three free radical detoxifying enzymes—copper/zinc superoxide dismutase, manganese superoxide dismutase, and catalase—for mutations in patients with PD. Patients and Methods: A total of 107 unrelated patients with PD from two PD populations (familial and sporadic) were screened for mutations in the genes of copper/zinc superoxide dismutase, manganese superoxide dismutase, and catalase by single-strand conformation analysis. The diagnosis of PD was based on the clinical observations of resting tremor, rigidity, and bradykinesia. Results: No mutations were identified. However, we did identify an amino acid substitution (glycine to aspartic acid) in exon 9 of the catalase gene in one patient; decreased red blood cell catalase activity was observed in this patient. Conclusion: Parkinson's disease is not caused by mutations in the genes of these three detoxifying enzymes. The exon 9 variant in the catalase gene in the one family with PD is most likely a silent mutation and not the genetic cause of PD in this family.

Widespread but cell type-specific expression of the mouse neurofibromatosis type 2 gene.

Abstract: Neurofibromatosis type 2 (NF2) is an autosomal dominant disease in which loss of function mutations of the NF2 gene lead to the development of schwannomas, meningiomas and juvenile cataracts. We studied the mouse NF2 homologue (Nf2) to determine its precise pattern of mRNA and protein expression. In situ hybridization showed that Nf2 is expressed in neuronal cells as well as in epithelial and fibre cells of the lens. The Nf2 protein, schwannomin, is expressed as a single protein isoform of approximately 80 kDa in neuronal and non-neuronal tissues. In Purkinje cells of the cerebellum and motor neurones of the spinal cord, the protein is in the cytoplasm. In non-neuronal tissues immunostaining showed expression in cells of the tunica intima of blood vessels. We conclude that there is a widespread but cell type-specific expression of schwannomin.

Adenylosuccinate lyase (ADSL) and infantile autism: Absence of previously reported point mutation

Abstract: Autism is a heterogeneous neuropsychiatric syndrome of unknown etiology. There is evidence that a deficiency in the enzyme adenylosuccinate lyase (ADSL), essential for de novo purine biosynthesis, could be involved in the pathogenesis of certain cases. A point mutation in the ADSL gene, resulting in a predicted serine-to-proline substitution and conferring structural instability to the mutant enzyme, has been reported previously in 3 affected siblings. In order to determine the prevalence of the mutation, we PCR-amplified the exon spanning the site of this mutation from the genomic DNA of patients fulfilling DSM-III-R criteria for autistic disorder. None of the 119 patients tested were found to have this mutation. Furthermore, on preliminary screening using singlestrand conformation polymorphism (SSCP), no novel mutations were detected in the coding sequence of four ADSL exons, spanning approximately 50% of the cDNA. In light of these findings, it appears that mutations in the ADSL gene represent a distinctly uncommon cause of autism.

Schwannomin: new insights into this member of the band 4.1 superfamily

Abstract: Neurofibromatosis type 2 (NF2) is an autosomal dominant disease characterized by the development of central nervous system tumours. The NF2 gene was recently cloned and found to encode a protein, s...

Le gène de la neurofibromatose de type 2

Abstract: La neurofibromatose de type 2 (NF2) est une maladie hereditaire predisposant, principalement, au developpement de schwannomes vestibulaires et de meningiomes, Bien que cette affection soit une maladie relativement rare, les schwannomes et les meningiomes, que l'on retrouve sous forme sporadique, representent une proportion importante des tumeurs cerebrales. Une strategie de clonage positionnel a permis d'identifier, sur le chromosome 22, un gene vraisemblablement deficient chez la plupart des malades atteints de NF2. Ce gene code pour une proteine de 66 kDa, nommee schwannomine ou merline, ayant une forte analogie de sequence avec les proteines de la famille ezrine-radixine-moesine (ERM). La schwannomine pourrait donc assurer le maintien d'interactions entre la membrane et le cytosquelette. Les etudes cytogenetiques des tumeurs, de meme que les mutations observees dans le genome de cellules tumorales, suggerent que la schwannomine joue un role de suppresseur de tumeur