Showing papers by "Guy A. Rouleau published in 2001"

A gene encoding a putative GTPase regulator is mutated in familial amyotrophic lateral sclerosis 2.

Abstract: Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile ALS and has been mapped to human chromosome 2q33. Here we report the identification of two independent deletion mutations linked to ALS2 in the coding exons of the new gene ALS2. These deletion mutations result in frameshifts that generate premature stop codons. ALS2 is expressed in various tissues and cells, including neurons throughout the brain and spinal cord, and encodes a protein containing multiple domains that have homology to RanGEF as well as RhoGEF. Deletion mutations are predicted to cause a loss of protein function, providing strong evidence that ALS2 is the causative gene underlying this form of ALS.

Neuron-Specific Expression of Mutant Superoxide Dismutase 1 in Transgenic Mice Does Not Lead to Motor Impairment

Abstract: Mutations were identified in the Cu/Zn superoxide dismutase gene (SOD1) in approximately 15% of patients with familial amyotrophic lateral sclerosis. Transgenic animals expressing mutant SOD1 in all tissues develop an ALS-like phenotype. To determine whether neuron-specific expression of mutant SOD1 is sufficient to produce such a phenotype, we generated transgenic animals carrying the G37R mutation that is associated with the familial form of ALS (FALS), which is driven by the neurofilament light chain promoter. The transgenic animals express high levels of the human SOD1 protein in neuronal tissues, especially in the large motor neurons of the spinal cord, but they show no apparent motor deficit at up to 1.5 years of age. Our animal model suggests that neuron-specific expression of ALS-associated mutant human SOD1 may not be sufficient for the development of the disease in mice.

Identification of a major susceptibility locus for restless legs syndrome on chromosome 12q.

Abstract: Restless legs syndrome (RLS) is a neurological disorder characterized by leg paresthesia associated with an irresistible urge to move that often interferes with nocturnal sleep, leading to chronic sleep deprivation. To map genes that may play a role in the vulnerability to RLS, a genomewide scan was conducted in a large French-Canadian family. Significant linkage was established on chromosome 12q, for a series of adjacent microsatellite markers with a maximum two-point LOD score of 3.42 (recombination fraction .05; P =6×10 −4 ; autosomal recessive mode of inheritance), whereas multipoint linkage calculations yielded a LOD score of 3.59. Haplotype analysis refined the genetic interval, positioning the RLS-predisposing gene in a 14.71-cM region between D12S1044 and D12S78. These findings represent the first mapping of a locus conferring susceptibility to RLS.

High resolution deletion analysis of constitutional DNA from neurofibromatosis type 2 (NF2) patients using microarray-CGH

Abstract: Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder whose hallmark is bilateral vestibular schwannoma. It displays a pronounced clinical heterogeneity with mild to severe forms. The NF ...

Mapping susceptibility genes for bipolar disorder: a pharmacogenetic approach based on excellent response to lithium.

Abstract: Genetic mapping studies in bipolar disorder (BD) have been hampered by the unclear boundaries of the phenotypic spectrum, and possibly, by the complexity of the underlying genetic mechanisms, and heterogeneity. Among the suggested approaches to circumvent these problems, a pharmacogenetic strategy has been increasingly proposed. Several studies have indicated that patients with BD who respond well to lithium prophylaxis constitute a biologically distinct subgroup. In this study we have conducted a complete genome scan using 378 markers spaced at an average distance of 10 cM in 31 families ascertained through excellent lithium responders. Response to lithium was evaluated prospectively with an average follow-up of 12 years. Evidence for linkage was found with a locus on chromosome 15q14 (ACTC, lod score = 3.46, locus-specific P-value = 0.000014) and suggestive results were observed for another marker on chromosome 7q11.2 (D7S1816, lod score = 2.68, locus-specific P-value = 0.00011). Other interesting findings were obtained with markers on chromosomes 6 and 22, namely D6S1050 (lod score = 2.0, locus-specific P-value = 0.00004) and D22S420 (lod score = 1.91). Nonparametric linkage analysis provided additional support for the role of these loci. Further analyses of these results suggested that the locus on chromosome 15q14 may be implicated in the etiology of BD, whereas the 7q11.2 locus may be relevant for lithium response. In conclusion, our results provide original evidence suggesting that loci on 15q14 and 7q11.2 may be implicated in the pathogenesis of BD responsive to lithium.

Improvement in the molecular diagnosis of Machado-Joseph disease

Abstract: Background: Direct detection of the gene mutation allows for the confirmation of the clinical diagnosis of Machado-Joseph disease (MJD), the most frequent cause of autosomal dominant spinocerebellar ataxia worldwide. Objective: To address the main difficulties in our national MJD predictive testing program. The first was the emergence of intermediate alleles, for which it is not yet possible to determine whether they will cause disease. The second was the issue of homoallelism, ie, homozygosity for 2 normal alleles with exactly the same (CAG)n length, which occurs in about 10% of all test results. Methods: A large pedigree with 1 affected patient carrying a 71 and a 51 CAG repeat and 2 asymptomatic relatives carrying the 51 CAG repeat and normal-size alleles underwent clinical and molecular studies. Intragenic haplotypes for these alleles were determined. A representative sample of the healthy population in the region was obtained to assess the distribution of the normal (CAG)n length. We established the genotype for 4 intragenic polymorphisms in the gene for MJD (MJD1 )i n 21 homoallelic individuals, to distinguish their 2 normal chromosomes. In addition, we developed a new Southern blot method to completely exclude cases of nonamplification of expanded alleles in the homoallelic individuals. Results: The study of the family in which the 51 CAG repeat was found suggests that the allele is apparently not associated with disease. These intermediate alleles were not present in a large sample of the healthy population from the same region. Intragenic polymorphisms allowed distinction of the 2 different normal alleles in all cases of homoallelism. The absence of an expanded allele was also confirmed by Southern blot. Conclusions: We propose an improved protocol for molecular testing for MJD. These strategies, developed to overcome the practical difficulties mostly in the presymptomatic and prenatal diagnosis of MJD, should prove useful for other polyglutamine-related disorders. Arch Neurol. 2001;58:1821-1827

Ancestral Origins of the Machado-Joseph Disease Mutation: A Worldwide Haplotype Study

Abstract: Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative disorder originally described in families of Portuguese-Azorean ancestry. The cloning of the MJD1 gene allowed identification of the disease in many other populations, and MJD is now known to be the most common cause of dominant spinocerebellar ataxia. The hypothesis that its present world distribution could result from the spread of an original founder mutation has been raised, both at historical and molecular levels. In the present study, we tested this hypothesis by linkage-disequilibrium analysis of tightly linked polymorphisms and by haplotype comparison, in 249 families from different countries. We typed five microsatellite markers surrounding the MJD1 locus (D14S1015, D14S995, D14S973, D14S1016, and D14S977), and three intragenic single–base-pair polymorphisms (A669TG/G669TG, C987GG/G987GG, and TAA1118/TAC1118). The results show two different haplotypes, specific to the island of origin, in families of Azorean extraction. In families from mainland Portugal, both Azorean haplotypes can be found. The majority of the non-Portuguese families also share the same intragenic haplotype seen in the families coming from the island of Flores, but at least three other haplotypes were seen. These findings suggest two introductions of the mutation into the Portuguese population. Worldwide, the sharing of one intragenic haplotype by the majority of the families studied implies a founder mutation in MJD.

Oligomerization of polyalanine expanded PABPN1 facilitates nuclear protein aggregation that is associated with cell death

Abstract: Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping, swallowing difficulties and proximal limb weakness. The autosomal dominant form of this disease is caused by short expansions of a (GCG) 6 6 repeat to (GCG) 8-13 in the PABPN1 gene, which results in the expansion of a polyalanine stretch from 10 to 12-17 alanines in the N-terminus of the protein. Mutated PABPN1 (mPABPN1) is able to induce nuclear protein aggregation and form filamentous nuclear inclusions, which are the pathological hall-marks of OPMD. PABPN1, when bound to poly(A) RNA, forms both linear filaments and discrete-sized, compact oligomeric particles in vitro. In the absence of poly(A) RNA, PABPN1 can form oligomers. Here we report that: (i) oligomerization of PABPN1 is mediated by two potential oligomerization domains (ODs); (ii) inactivating oligomerization of mPABPN1 by deletions of 6-8 amino acids in either of the ODs prevents nuclear protein aggregation; (iii) expression of mPABPN1 in COS-7 cells is associated with cell death; and (iv) preventing nuclear protein aggregation by inactivating oligomerization of mPABPN1 significantly reduces cell death. These findings suggest that oligomerization of PABPN1 plays a crucial role in the formation of OPMD nuclear protein aggregation, while the expanded polyalanine stretch is necessary but not sufficient to induce OPMD protein aggregation, and that the nuclear protein aggregation might be toxic and cause cell death. These observations also imply that inactivation of oligomerization of mPABPN1 might be a useful therapeutic strategy for OPMD.

The genomic structure and expression of MJD, the Machado-Joseph disease gene

Abstract: Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative disorder that is clinically characterized by cerebellar ataxia and various associated symptoms. The disease is caused by an unstable expansion of the CAG repeat in the MJD gene. This gene is mapped to chromosome 14q32.1. To determine its genomic structure, we constructed a contig composed of six cosmid clones and eight bacterial artificial chromosome (BAC) clones. It spans approximately 300 kb and includes MJD. We also determined the complete sequence (175,330 bp) of B445M7, a human BAC clone that contains MJD. The MJD gene was found to span 48,240 bp and to contain 11 exons. Northern blot analysis showed that MJD mRNA is ubiquitously expressed in human tissues, and in at least four different sizes; namely, 1.4, 1.8, 4.5, and 7.5 kb. These different mRNA species probably result from differential splicing and polyadenylation, as shown by sequences of the 21 independent cDNA clones isolated after the screening of four human cDNA libraries prepared from whole brain, caudate, retina, and testis. The sequences of these latter clones relative to the MJD gene in B445M7 indicate that there are three alternative splicing sites and eight polyadenylation signals in MJD that are used to generate the differently sized transcripts.

Compound heterozygous D90A and D96N SOD1 mutations in a recessive amyotrophic lateral sclerosis family

Abstract: We describe a French amyotrophic lateral sclerosis (ALS) family with two distinct mutations in the Cu/Zn superoxide dismutase (SOD1) gene. The D90A mutation has been well described and clearly shown to cause recessive ALS. In this family, affected individuals are heterozygous for the D90A mutation and also carry a single copy of a novel SOD1 mutation, D96N. We propose that in this family both mutations are required for the development of disease.

Mutations of the Notch3 Gene in Non-Caucasian Patients with Suspected CADASIL Syndrome

Abstract: The Notch3 gene has been recently identified as a causative gene for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). To investigate the genetic contribution of Notch mutations in familial cases with vascular leukoencephalopathy, we screened 13 patients from 11 unrelated families, which were selected on the basis of magnetic resonance imaging findings and positive family history. We identified three different missense mutations in 5 patients from 4 families. Two (Arg90Cys and Arg133Cys) are the same as previously reported in Caucasian patients, the other (Cys174Phe) is a novel mutation causing a loss of a cysteine in epidermal-growth-factor-like repeats of Notch3. These data indicate that the CADASIL Notch3 mutations were found in approximately 35% of familial cases with leukoencephalopathy, suggesting genetic heterogeneity of the disease.

Identification of three polymorphisms in the translated region of PLC-γ1 and their investigation in lithium responsive bipolar disorder

Abstract: Recently, we have found an association between bipolar disorder patients who are excellent responders to lithium prophylaxis and a polymorphic marker located in the first intron of the phospholipase C-γ1 gene (PLC-γ1) [Turecki et al., 1998: Mol Psychiatry 3:534-538]. As this variant is not known to be functional, we searched for other markers within the coding region, using single-strand conformational polymorphism (SSCP) analysis. We have identified three polymorphic sites localized in three different exons of the PLC-γ1 gene (exons 9, 26, 31). Variation studies of these potentially functional sites in a group of 133 bipolar patients with an excellent response to lithium prophylaxis and a comparison group of 99 healthy controls showed no difference in genotype distributions for exon 9 (chi-square = 1.41, df = 2, P = 0.49), exon 26 (chi-square = 2.26, df = 2, P = 0.13), or exon 31 (chi-square = 1.41, df=2, P = 0.49). Similar results were observed for allele distributions. These results suggest that our previous findings were not the result of linkage disequilibrium with these variants.

Oculopharyngeal muscular dystrophy: What's new?

Abstract: The authors place autosomal dominant oculopharyngeal muscular dystrophy in a historical perspective, look at the genealogy involved, and review the genetic studies. In addition to summarizing what happens at the histopathological level, they examine the clinical characteristics of this late-onset dystrophy. Based on this knowledge, they try to present their rationale for the surgical treatment of the eyelid ptosis, taking into account that this disease is progressive and that treatment should be planned for the lifetime of the patient. Three representative cases are illustrated.

Alopecia areata universalis in an infant.

Abstract: Background Alopecia areata (AA) is common during childhood and rarely reported in infants. The four reported cases of AA in infants all exhibited circumscribed patches of alopecia that appeared at birth or shortly thereafter.

A founder mutation in French-Canadian families with X-linked hereditary neuropathy.

Abstract: Introduction: Le but de cette etude etait d'identifier les mutations du gene de la connexine 32 chez des familles canadiennes-francaises atteintes de la maladie de Charcot-Marie-Tooth liee a l'X (CMTX). Methodes: L'analyse moleculaire a ete faite par polymorphisme de conformation d'ADN simple brin non isotopique et sequencage. L'evaluation clinique a ete effectuee selon l'echelle definie par le Consortium HMSN Europeen. Resultats: Dans une famille, la mutation Arg 142Trp a ete localisee dans le domaine transmembranaire III alors que chez quatre autres familles, nous avons identifie une nouvelle mutation (Ser26Trp) localisee dans le domaine transmembranaire I du gene Cx32. L'analyse des haplotypes a montre que ces quatre familles sont apparentees et suggere qu'il s'agit d'une mutation fondatrice. Seize patients de ces quatre familles ont ete etudies. Tel que prevu, tous les hommes atteints etaient plus severement atteints que les femmes et tous les patients atteints presentaient des caracteristiques electrophysiologiques de demyelinisation. Conclusion: Notre etude suggere que la mutation Ser26Trp peut causer une neuropathie demyelinisante primaire qui n'est pas associee a un phenotype clinique specifique. Nous avons egalement des donnees qui demontrent que la majorite des familles ont un ancetre commun.