Nicolas Dupré

The K-Cl cotransporter KCC3 is mutant in a severe peripheral neuropathy associated with agenesis of the corpus callosum

Peripheral neuropathy associated with agenesis of the corpus callosum (ACCPN) is a severe sensorimotor neuropathy associated with mental retardation, dysmorphic features and complete or partial agenesis of the corpus callosum. ACCPN is transmitted in an autosomal recessive fashion and is found at a high frequency in the province of Quebec, Canada. ACCPN has been previously mapped to chromosome 15q. The gene SLC12A6 (solute carrier family 12, member 6), which encodes the K+–Cl− transporter KCC3 and maps within the ACCPN candidate region, was screened for mutations in individuals with ACCPN. Four distinct protein-truncating mutations were found: two in the French Canadian population and two in non–French Canadian families. The functional consequence of the predominant French Canadian mutation (2436delG, Thr813fsX813) was examined by heterologous expression of wildtype and mutant KCC3 in Xenopus laevis oocytes; the truncated mutant is appropriately glycosylated and expressed at the cellular membrane, where it is non-functional. Mice generated with a targeted deletion of Slc12a6 have a locomotor deficit, peripheral neuropathy and a sensorimotor gating deficit, similar to the human disease. Our findings identify mutations in SLC12A6 as the genetic lesion underlying ACCPN and suggest a critical role for SLC12A6 in the development and maintenance of the nervous system.

Mutational spectrum of the CHAC gene in patients with chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is an autosomal recessive neurological disorder whose characteristic features include hyperkinetic movements and abnormal red blood cell morphology. Mutations in the CHAC gene on 9q21 were recently found to cause chorea-acanthocytosis. CHAC encodes a large, novel protein with a yeast homologue implicated in protein sorting. In this study, all 73 exons plus flanking intronic sequence in CHAC were screened for mutations by denaturing high-performance liquid chromatography in 43 probands with ChAc. We identified 57 different mutations, 54 of which have not previously been reported, in 39 probands. The novel mutations comprise 15 nonsense, 22 insertion/deletion, 15 splice-site and two missense mutations and are distributed throughout the CHAC gene. Three mutations were found in multiple families within this or our previous study. The preponderance of mutations that are predicted to cause absence of gene product is consistent with the recessive inheritance of this disease. The high proportion of splice-site mutations found is probably a reflection of the large number of exons that comprise the CHAC gene. The CHAC protein product, chorein, appears to have a certain tolerance to amino-acid substitutions since only two out of nine substitutions described here appear to be pathogenic.

Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum

Hereditary motor and sensory neuropathy associated with agenesis of the corpus callosum (OMIM 218000) is an autosomal recessive disease of early onset characterized by a delay in developmental milestones, a severe sensory‐motor polyneuropathy with areflexia, a variable degree of agenesis of the corpus callosum, amyotrophy, hypotonia, and cognitive impairment. Although this disorder has rarely been reported worldwide, it has a high prevalence in the Saguenay‐Lac‐St‐Jean region of the province of Quebec (Canada) predominantly because of a founder effect. The gene defect responsible for this disorder recently has been identified, and it is a protein‐truncating mutation in the SLC12A6 gene, which codes for a cotransporter protein known as KCC3. Herein, we provide the first extensive review of this disorder, covering epidemiological, clinical, and molecular genetic studies. Ann Neurol 2002;54:9–18

Chapter 9 Hereditary Ataxias and Spastic Parapareses in Northeastern Canada

Publisher Summary This chapter summarizes the current understanding of the main hereditary ataxias and spastic parapareses that are particular to northeastern Canada. The following neurogenetic disorders were first identified in patients from northeastern Canada: ataxia with oculomotor apraxia type 2, autosomal recessive spastic ataxia of Charlevoix–Saguenay, hereditary sensory and autonomic neuropathy type 2, recessive ataxia of the Beauce, spastic ataxia 1, hereditary motor and sensory neuropathy with agenesis of the corpus callosum, and autosomal dominant sensory ataxia. It has been demonstrated for many inherited diseases that historical events have shaped the various regional gene pools of Quebec and the Maritime Provinces. In doing so, it has given rise to the increased prevalence of some rare diseases due to founder effects. The study of the more common and homogenous of these diseases has been largely completed. The regional populations of Canada will still allow the identification of new rarer forms of ataxias and parapareses and contribute to the uncovering of their mutated genes.

The Project MinE databrowser: bringing large-scale whole-genome sequencing in ALS to researchers and the public.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive fatal neurodegenerative disease affecting 1 in 350 people. The aim of Project MinE is to elucidate the pathophysiology of ALS through whole-genome sequencing at least 15,000 ALS patients and 7,500 controls at 30X coverage. Here, we present the Project MinE data browser (databrowser.projectmine.com), a unique and intuitive one-stop, open-access server that provides detailed information on genetic variation analyzed in a new and still growing set of 4,366 ALS cases and 1,832 matched controls. Through its visual components and interactive design, the browser specifically aims to be a resource to those without a biostatistics background and allow clinicians and preclinical researchers to integrate Project MinE data into their own research. The browser allows users to query a transcript and immediately access a unique combination of detailed (meta)data, annotations and association statistics that would otherwise require analytic expertise and visits to scattered resources.

Exome sequencing revealed PMM2 gene mutations in a French-Canadian family with congenital atrophy of the cerebellum

Two affected and one unaffected siblings from a French-Canadian family were evaluated in our neurogenetic clinic. The oldest brother had intentional and postural hand tremor while his youngest sister presented mild ataxia, a similar hand tremor and global developmental delay. Brain MRIs of the two affected family members further revealed a significant cerebellar atrophy. For this study we conducted a whole exome sequencing (WES) investigation using genomic DNA prepared from the affected brother and sister, alongside DNA prepared from their unaffected mother, and identified two mutations previously reported to cause a rare disorder known as Congenital Disorder of Glycosylation, type Ia (CDG1A) (OMIM #212065). This study emphasizes how the diagnosis of patients presenting a mild tremor phenotype associated with cerebellar atrophy may benefit from WES in establishing genetic defects associated with their conditions.