Showing papers by "Guy A. Rouleau published in 2012"

Exome Sequencing Identifies FUS Mutations as a Cause of Essential Tremor

Abstract: Essential tremor (ET) is a common neurodegenerative disorder that is characterized by a postural or motion tremor. Despite a strong genetic basis, a gene with rare pathogenic mutations that cause ET has not yet been reported. We used exome sequencing to implement a simple approach to control for misdiagnosis of ET, as well as phenocopies involving sporadic and senile ET cases. We studied a large ET-affected family and identified a FUS p.Gln290∗ mutation as the cause of ET in this family. Further screening of 270 ET cases identified two additional rare missense FUS variants. Functional considerations suggest that the pathogenic effects of ET-specific FUS mutations are different from the effects observed when FUS is mutated in amyotrophic lateral sclerosis cases; we have shown that the ET FUS nonsense mutation is degraded by the nonsense-mediated-decay pathway, whereas amyotrophic lateral sclerosis FUS mutant transcripts are not.

Mutations in C5ORF42 Cause Joubert Syndrome in the French Canadian Population

Abstract: Joubert syndrome (JBTS) is an autosomal-recessive disorder characterized by a distinctive mid-hindbrain malformation, developmental delay with hypotonia, ocular-motor apraxia, and breathing abnormalities. Although JBTS was first described more than 40 years ago in French Canadian siblings, the causal mutations have not yet been identified in this family nor in most French Canadian individuals subsequently described. We ascertained a cluster of 16 JBTS-affected individuals from 11 families living in the Lower St. Lawrence region. SNP genotyping excluded the presence of a common homozygous mutation that would explain the clustering of these individuals. Exome sequencing performed on 15 subjects showed that nine affected individuals from seven families (including the original JBTS family) carried rare compound-heterozygous mutations in C5ORF42. Two missense variants (c.4006C>T [p.Arg1336Trp] and c.4690G>A [p.Ala1564Thr]) and a splicing mutation (c.7400+1G>A), which causes exon skipping, were found in multiple subjects that were not known to be related, whereas three other truncating mutations (c.6407del [p.Pro2136Hisfs∗31], c.4804C>T [p.Arg1602∗], and c.7477C>T [p.Arg2493∗]) were identified in single individuals. None of the unaffected first-degree relatives were compound heterozygous for these mutations. Moreover, none of the six putative mutations were detected among 477 French Canadian controls. Our data suggest that mutations in C5ORF42 explain a large portion of French Canadian individuals with JBTS.

Mutant TDP-43 and FUS Cause Age-Dependent Paralysis and Neurodegeneration in C. elegans

Abstract: Mutations in the DNA/RNA binding proteins TDP-43 and FUS are associated with Amyotrophic Lateral Sclerosis and Frontotemporal Lobar Degeneration. Intracellular accumulations of wild type TDP-43 and FUS are observed in a growing number of late-onset diseases suggesting that TDP-43 and FUS proteinopathies may contribute to multiple neurodegenerative diseases. To better understand the mechanisms of TDP-43 and FUS toxicity we have created transgenic Caenorhabditis elegans strains that express full-length, untagged human TDP-43 and FUS in the worm's GABAergic motor neurons. Transgenic worms expressing mutant TDP-43 and FUS display adult-onset, age-dependent loss of motility, progressive paralysis and neuronal degeneration that is distinct from wild type alleles. Additionally, mutant TDP-43 and FUS proteins are highly insoluble while wild type proteins remain soluble suggesting that protein misfolding may contribute to toxicity. Populations of mutant TDP-43 and FUS transgenics grown on solid media become paralyzed over 7 to 12 days. We have developed a liquid culture assay where the paralysis phenotype evolves over several hours. We introduce C. elegans transgenics for mutant TDP-43 and FUS motor neuron toxicity that may be used for rapid genetic and pharmacological suppressor screening.

Mutations in TMEM231 cause Joubert syndrome in French Canadians

Abstract: Background Joubert syndrome (JBTS) is a predominantly autosomal recessive disorder characterised by a distinctive midhindbrain malformation, oculomotor apraxia, breathing abnormalities and developmental delay. JBTS is genetically heterogeneous, involving genes required for formation and function of non-motile cilia. Here we investigate the genetic basis of JBTS in 12 French–Canadian (FC) individuals. Methods and results Exome sequencing in all subjects showed that six of them carried rare compound heterozygous mutations in CC2D2A or C5ORF42 , known JBTS genes. In addition, three individuals (two families) were compound heterozygous for the same rare mutations in TMEM231 (c.12T>A[p.Tyr4*]; c.625G>A[p.Asp209Asn]). All three subjects showed a severe neurological phenotype and variable presence of polydactyly, retinopathy and renal cysts. These mutations were not detected among 385 FC controls. TMEM231 has been previously shown to localise to the ciliary transition zone, and to interact with several JBTS gene products in a complex involved in the formation of the diffusion barrier between the cilia and plasma membrane. siRNA knockdown of TMEM231 was also shown to affect barrier integrity, resulting in a reduction of cilia formation and ciliary localisation of signalling receptors. Conclusions Our data suggest that mutations in TMEM231 cause JBTS, reinforcing the relationship between this condition and the disruption of the barrier at the ciliary transition zone.

Phenotype and genotype analysis in amyotrophic lateral sclerosis with TARDBP gene mutations

Abstract: Objective: To describe the phenotype and phenotype–genotype correlations in patients with amyotrophic lateral sclerosis (ALS) with TARDBP gene mutations. Methods: French TARDBP + patients with ALS (n = 28) were compared first to 3 cohorts: 737 sporadic ALS (SALS), 192 nonmutated familial ALS (FALS), and 58 SOD1 + FALS, and then to 117 TARDBP + cases from the literature. Genotype–phenotype correlations were studied for the most frequent TARDBP mutations. Results: In TARDBP + patients, onset was earlier ( p = 0.0003), upper limb (UL) onset was predominant ( p = 0.002), and duration was longer ( p = 0.0001) than in patients with SALS. TARDBP + and SOD1 + groups had the longest duration but diverged for site of onset: 64.3% UL onset for TARDBP + and 74.1% on lower limbs for SOD1 + ( p p = 0.02). The type of mutation influenced survival ( p TARDBP super rich glycine-residue domain, was associated with the worst survival (27 months). Conclusion: Differences in phenotype between the groups as well as the differential influence of TARBDP mutations on survival may help physicians in ALS management and allow refining the strategy of genetic diagnosis.

Unruptured intracranial aneurysms in the Familial Intracranial Aneurysm and International Study of Unruptured Intracranial Aneurysms cohorts: differences in multiplicity and location

Abstract: Object Familial predisposition is a recognized nonmodifiable risk factor for the formation and rupture of intracranial aneurysms (IAs). However, data regarding the characteristics of familial IAs are limited. The authors sought to describe familial IAs more fully, and to compare their characteristics with a large cohort of nonfamilial IAs. Methods The Familial Intracranial Aneurysm (FIA) study is a multicenter international study with the goal of identifying genetic and other risk factors for formation and rupture of IAs in a highly enriched population. The authors compared the FIA study cohort with the International Study of Unruptured Intracranial Aneurysms (ISUIA) cohort with regard to patient demographic data, IA location, and IA multiplicity. To improve comparability, all patients in the ISUIA who had a family history of IAs or subarachnoid hemorrhage were excluded, as well as all patients in both cohorts who had a ruptured IA prior to study entry. Results Of 983 patients enrolled in the FIA study wi...

VAMP1 Mutation Causes Dominant Hereditary Spastic Ataxia in Newfoundland Families

Abstract: Our group previously described and mapped to chromosomal region 12p13 a form of dominantly inherited hereditary spastic ataxia (HSA) in three large Newfoundland (Canada) families. This report identifies vesicle-associated membrane protein 1 (VAMP1), which encodes a critical protein for synaptic exocytosis, as the responsible gene. In total, 50 affected individuals from these families and three independent probands from Ontario (Canada) share the disease phenotype together with a disruptive VAMP1 mutation that affects a critical donor site for the splicing of VAMP1 isoforms. This mutation leads to the loss of the only VAMP1 isoform (VAMP1A) expressed in the nervous system, thus highlighting an association between the well-studied VAMP1 and a neurological disorder. Given the variable phenotype seen in the affected individuals examined here, we believe that VAMP1 should be tested for mutations in patients with either ataxia or spastic paraplegia.

Expanded ATXN3 frameshifting events are toxic in Drosophila and mammalian neuron models

Abstract: Spinocerebellar ataxia type 3 is caused by the expansion of the coding CAG repeat in the ATXN3 gene. Interestingly, a -1 bp frameshift occurring within an (exp)CAG repeat would henceforth lead to translation from a GCA frame, generating polyalanine stretches instead of polyglutamine. Our results show that transgenic expression of (exp)CAG ATXN3 led to -1 frameshifting events, which have deleterious effects in Drosophila and mammalian neurons. Conversely, transgenic expression of polyglutamine-encoding (exp)CAA ATXN3 was not toxic. Furthermore, (exp)CAG ATXN3 mRNA does not contribute per se to the toxicity observed in our models. Our observations indicate that expanded polyglutamine tracts in Drosophila and mouse neurons are insufficient for the development of a phenotype. Hence, we propose that -1 ribosomal frameshifting contributes to the toxicity associated with (exp)CAG repeats.

Schizophrenia genetics: putting all the pieces together.

Abstract: Schizophrenia is a major mental disorder characterized by a deep disruption of the thinking process and of emotional response. For many decades, genetics studies have yielded little success in identifying genetic factors responsible for the disease. However, with the recent breakthroughs in genome analysis technologies, the field of the genetics of schizophrenia has progressed a lot in the last years. Both common and rare variants have been successfully associated with the disease and a particular emphasis has been made on rare copy number variations. Recently, a new paradigm linking de novo mutations to the genetic mechanism of schizophrenia has been unravelled. The aim of this review is to discuss the most important genetic studies made in the field to give a general perspective of where to go in the future.

Novel FUS deletion in a patient with juvenile amyotrophic lateral sclerosis.

Abstract: Background Juvenile amyotrophic lateral sclerosis (JALS) refers to a form of amyotrophic lateral sclerosis (ALS) in which a progressive upper and lower motor neuron degeneration begins before 25 years of age. It is generally associated with slow disease progression. During the past decade, a number of genes have been reported to cause JALS. Mutations in the ALSIN gene cause JALS type 2 (ALS2) as well as juvenile primary lateral sclerosis and infantile-onset ascending spastic paralysis. Mutations in the SETX gene can also sometimes lead to JALS. Conversely, mutations in SOD1, TARDBP, and FUS typically cause pure ALS, with adult onset between 46 and 56 years of age and usually rapid progression over 3 to 5 years. Recently, a few mutations in FUS have been associated with juvenile-onset of ALS characterized by a very rapid progression. Objective To investigate the genetics of a patient with juvenile-onset ALS. Design and Patient We sequenced all the coding exons of SOD1, TARDBP, and FUS in a 19-year-old patient experiencing rapid degeneration of upper and lower motor neurons. Results A novel 1–base pair deletion was detected in exon 14 of the FUS gene, leading to a frameshift and the integration of 33 new amino acids. The variant p.R495QfsX527 is located in the highly conserved, extreme C terminal of the FUS protein, where most of the mutations in FUS have been identified. The variant was also identified in the unaffected 47-year-old mother of the patient, who remains asymptomatic. Conclusions Our finding, along with other research, further confirms that FUS mutations can lead to an early-onset malignant form of ALS. In addition, our data lend additional support to the notion that disruption of the conserved C terminal of FUS is critical for developing ALS.

Identification of a novel in-frame de novo mutation in SPTAN1 in intellectual disability and pontocerebellar atrophy

Abstract: Heterozygous in-frame mutations (p.E2207del and p.R2308_M2309dup) in the α-II subunit of spectrin (SPTAN1) were recently identified in two patients with intellectual disability (ID), infantile spasms (IS), hypomyelination, and brain atrophy. These mutations affected the C-terminal domain of the protein, which contains the nucleation site of the α/β spectrin heterodimer. By screening SPTAN1 in 95 patients with idiopathic ID, we found a de novo in-frame mutation (p.Q2202del) in the same C-terminal domain in a patient with mild generalized epilepsy and pontocerebellar atrophy, but without IS, hypomyelination, or other brain structural defects, allowing us to define the core phenotype associated with these C-terminal SPTAN1 mutations. We also found a de novo missense variant (p.R566P) of unclear clinical significance in a patient with non-syndromic ID. These two mutations induced different patterns of aggregation between spectrin subunits in transfected neuronal cell lines, providing a paradigm for the classification of candidate variants.

Synapsin II is involved in the molecular pathway of lithium treatment in bipolar disorder.

Abstract: Bipolar disorder (BD) is a debilitating psychiatric condition with a prevalence of 1–2% in the general population that is characterized by severe episodic shifts in mood ranging from depressive to manic episodes. One of the most common treatments is lithium (Li), with successful response in 30–60% of patients. Synapsin II (SYN2) is a neuronal phosphoprotein that we have previously identified as a possible candidate gene for the etiology of BD and/or response to Li treatment in a genome-wide linkage study focusing on BD patients characterized for excellent response to Li prophylaxis. In the present study we investigated the role of this gene in BD, particularly as it pertains to Li treatment. We investigated the effect of lithium treatment on the expression of SYN2 in lymphoblastoid cell lines from patients characterized as excellent Li-responders, non-responders, as well as non-psychiatric controls. Finally, we sought to determine if Li has a cell-type-specific effect on gene expression in neuronal-derived cell lines. In both in vitro models, we found SYN2 to be modulated by the presence of Li. By focusing on Li-responsive BD we have identified a potential mechanism for Li response in some patients.

Loss of Neuronal Potassium/Chloride Cotransporter 3 (KCC3) Is Responsible for the Degenerative Phenotype in a Conditional Mouse Model of Hereditary Motor and Sensory Neuropathy Associated with Agenesis of the Corpus Callosum

Abstract: Disruption of the potassium/chloride cotransporter 3 (KCC3), encoded by the SLC12A6 gene, causes hereditary motor and sensory neuropathy associated with agenesis of the corpus callosum (HMSN/ACC), a neurodevelopmental and neurodegenerative disorder affecting both the peripheral nervous system and CNS. However, the precise role of KCC3 in the maintenance of ion homeostasis in the nervous system and the pathogenic mechanisms leading to HMSN/ACC remain unclear. We established two Slc12a6 Cre/LoxP transgenic mouse lines expressing C-terminal truncated KCC3 in either a neuron-specific or ubiquitous fashion. Our results suggest that neuronal KCC3 expression is crucial for axon volume control. We also demonstrate that the neuropathic features of HMSN/ACC are predominantly due to a neuronal KCC3 deficit, while the auditory impairment is due to loss of non-neuronal KCC3 expression. Furthermore, we demonstrate that KCC3 plays an essential role in inflammatory pain pathways. Finally, we observed hypoplasia of the corpus callosum in both mouse mutants and a marked decrease in axonal tracts serving the auditory cortex in only the general deletion mutant. Together, these results establish KCC3 as an important player in both central and peripheral nervous system maintenance.

Identification of novel genes involved in migraine.

Abstract: Background.— Migraine is a common form of headache affecting about 12% of the population. Genetic studies in the rare form of familial hemiplegic migraine have identified mutations in 3 genes (CACNA1A, ATP1A2, and SCN1A) encoding proteins involved in ion homeostasis and suggesting that other such genes may be involved in the more common forms of migraine. Objectives.— To test this proposition, the coding regions of 150 brain-expressed genes involved in ion homeostasis (ion channels, transporters, exchangers, and accessory subunits) were systematically screened to identify DNA variants in a group of 110 migraine probands and 250 control samples. Methods.— DNA variants were analyzed using a number of complementary in silico approaches. Results.— Several genes encoding potassium channels, including KCNK18, KCNG4, and KCNAB3, were identified as potentially linked to migraine. In situ hybridization studies of the mouse Kcnk18 ortholog show that it is developmentally expressed in the trigeminal and dorsal root ganglia, further supporting the involvement of this gene in migraine pathogenesis. Conclusions.— Our study is the first to link variations in these K+ channel genes to migraine, thus expanding on the view of migraine as a channelopathy and providing potential molecular targets for further study and therapeutic applications.

C9orf72 hexanucleotide repeat expansions as the causative mutation for chromosome 9p21-linked amyotrophic lateral sclerosis and frontotemporal dementia.

Abstract: Objective To further assess the presence of a large hexanucleotide repeat expansion in the first intron of the C9orf72 gene identified as the genetic cause of chromosome 9p21–linked amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD) in 4 unrelated families with a conclusive linkage to c9ALS/FTD. Design A repeat-primed polymerase chain reaction assay. Setting Academic research. Participants Affected and unaffected individuals from 4 ALS/FTD families. Main Outcome Measure The amplified C9orf72 repeat expansion. Results We show that the repeat is expanded in and segregated perfectly with the disease in these 4 pedigrees. Conclusion Our findings further confirm the C9orf72 hexanucleotide repeat expansion as the causative mutation for c9ALS/FTD and strengthen the hypothesis that ALS and FTD belong to the same disease spectrum.

De novo mutations in neurological and psychiatric disorders: effects, diagnosis and prevention

Abstract: Neurological and psychiatric disorders account for a considerable proportion of the global disease burden. Although there is a high heritability and a significant genetic component in these disorders, the genetic cause of most cases has yet to be identified. Advances in DNA sequencing allowing the analysis of the whole human genome in a single experiment have led to an acceleration of the discovery of the genetic factors associated with human disease. Recent studies using these platforms have highlighted the important role of de novo mutations in neurological and psychiatric disorders. These findings have opened new avenues into the understanding of genetic disease mechanisms. These discoveries, combined with the increasing ease with which we can sequence the human genome, have important implications for diagnosis, prevention and treatment. Here, we present an overview of the recent discovery of de novo mutations using key examples of neurological and psychiatric disorders. We also discuss the impact of technological developments on diagnosis and prevention.

The FUS about arginine methylation in ALS and FTLD

Abstract: In a time where links between amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) neurodegeneration are becoming increasingly clear, it is important to establish the convergent and divergent mechanisms responsible for this. Accordingly, Dormann et al (2012) have identified that methylation of the Fused in sarcoma (FUS) RGG3 domain is involved in the cytoplasmic mislocalisation of ALS‐FUS mutants, through a transportin‐dependent mechanism. By contrast, hypomethylation in this domain may play a role in the aberrant accumulation of FUS in FTLD‐FUS. This work showcases arginine methylation as a phenomenon to watch out for in neurodegenerative pathology.

Expanding the differential diagnosis of inherited neuropathies with non‐uniform conduction: Andermann syndrome

Abstract: Uniform conduction slowing has been considered a characteristic of inherited demyelinating neuropathies. We present an 18-year-old girl, born from first cousins, that presented a late motor and psychological development, cerebellar ataxia, facial diplegia, abnormal eye movement, scoliosis, and corpus callosum agenesis, whose compound muscle action potentials were slowed and dispersed. A mutation was found on KCC3 gene, confirming Andermann syndrome, a disease that must be included in the differential diagnosis of inherited neuropathies with non-uniform conduction slowing.

Rare variants in complex traits: novel identification strategies and the role of de novo mutations.

Abstract: Following the limited success of linkage and association studies aimed at identifying the genetic causes of common neurodevelopmental syndromes like autism and schizophrenia, complex traits such as these have recently been considered under the 'common disease-rare variant' hypothesis. Prior to this hypothesis, the study of candidate genes has enabled the discovery of rare variants in complex disorders, and in turn some of these variants have highlighted the genetic contribution of de novo variants. De novo variants belong to a subcategory of spontaneous rare variants that are largely associated with sporadic diseases, which include some complex psychiatric disorders where the affected individuals do not transmit the genetic defects they carry because of their reduced reproductive fitness. Interestingly, recent studies have demonstrated the rate of germline de novo mutations to be higher in individuals with complex psychiatric disorders by comparison to what is seen in unaffected control individuals; moreover, de novo mutations carried by affected individuals have generally been more deleterious than those observed in control individuals. Advanced sequencing technologies have recently enabled the undertaking of massive parallel sequencing projects that can cover the entire coding sequences (exome) or genome of several individuals at once. Such advances have thus fostered the emergence of novel genetic hypotheses and ideas to investigate disease-causative genetic variations. The genetic underpinnings of a number of sporadic complex diseases is now becoming partly explained and more major breakthroughs for complex traits genomics should be expected in the near future.

Endoplasmic reticulum lipid rafts and upper motor neuron degeneration.

Abstract: Primary lateral sclerosis (PLS) is a neurodegenerative disease of upper motor neurons affecting the corticospinal and corticobulbar tracts, leading to progressive spinal and bulbar spasticity. Typically, sporadically affected individuals first experience muscle weakness in the lower limbs, followed by spasticity of the upper extremities and the bulbar muscles. The average disease duration is 19 years, and the mean age of onset is 50 years. Interestingly, a juvenile familial form of the disease exists, known as juvenile PLS (JPLS), with affected cases experiencing the first symptoms in early childhood. Recessive mutations in ALS2, SPG11, and SIGMAR1 genes have been reported in JPLS patients, whereas variants in FIG4 and have been associated with the adult form of the disease. In this issue of Annals of Neurology, Al-Saif et al. describe a consanguineous recessive family with 4 members affected with JPLS. They report a shared ERLIN2 substitution located in the acceptor splice site of intron 6 of the long isoform of the gene, leading to the integration of 23 intronic nucleotides located upstream of exon 8 that leads to a premature stop codon. ERLIN2, a component of endoplasmic reticulum (ER) lipid rafts, has been previously linked to hereditary spastic paraplegia (SPG18), a group of diseases that overlaps with JPLS. Another consanguineous family segregating juvenile amyotrophic lateral sclerosis was previously reported to be linked to a missense mutation in another component of ER lipid rafts, SIGMAR1. Interestingly, the previously reported SIGMAR1 untranslated region variants in frontotemporal/motor neuron disease families have turned out to be a false result, as these families are now known to segregate the C9ORF72 repeat expansions, located in the same chromosomal region. Interestingly, the RNF170 gene was previously associated with neurodegeneration when autosomal dominant mutations were identified in patients affected with sensory ataxia. It is interesting to note that the RNF170 protein also interacts with ER lipid rafts. In fact, inositol 1,4,5-triphosphate (IP3) receptors play a significant role in cell signaling by inducing conformational changes that permit Ca2þ to flow from the ER into the cytosol. Upon activation, these receptors are degraded by the ubiquitin–proteasome pathway. ERLIN2 is responsible for IP3 receptor selection for endoplasmic reticulum-associated protein degradation (ERAD) by binding IP3 receptors right after activation. RNF170 associates with ERLIN2 to mediate IP3 receptor ubiquitination and processing by the ERAD. Consequently, depletion of ERLIN2 results in inhibition of RNF170 binding and inhibition of ERAD, possibly provoking an accumulation of IP3 receptors and an overflow of Ca 2þ out of the ER. In addition, another interesting study demonstrated that conformational change in the ER affected by mutations in RTN2 known to cause hereditary spastic paraplegia 12 (SPG12), results in abnormalities within distal portions of long motor axons and in their presynaptic terminals. It was also demonstrated that aberrant reticulon proteins impair axonal smooth ER and disrupt the microtubule cytoskeleton and mitochondria. This further reinforces the implication of ER stress in neurodegeneration, and the involvement of ERLIN2 in upper motor neuron dysfunction. Considering that polymorphisms in ER lipid raft genes have been identified in JPLS, hereditary spastic paraplegia (HSP), and possibly amyotrophic lateral sclerosis, that a change in ER conformation has been linked to HSP, and that lipid raft signaling is important in the pathogenesis of Alzheimer disease (AD), Parkinson disease, and prion diseases which were all previously associated with motor neuron disease, this study underlines the important role of abnormal ER function in a wide spectrum of motor neuron diseases. Importantly, an association was recently reported between a variant in SIGMAR1 and AD, which reinforces the relationship between dementia and motor neuron diseases. It may be relevant to screen other ER-related genes for mutations in this specific subgroup of neurodegenerative diseases. Further molecular functioning studies are also needed to elucidate the contribution of ER lipid rafts in neurodegeneration.

Familial ALS: less common than we think?

Abstract: Amyotrophic lateral sclerosis (ALS) is an adult onset motor neuron disease that affects both upper and lower motor neurons. The disease progresses rapidly, with 70%–80% of individuals dying within 5 years, typically from respiratory failure.1 Familial cases of ALS (FALS), where there is co-occurrence of ALS in first-, second- or third-degree relatives, have been reported to represent about 10% of all cases.2 However, because familial and sporadic ALS cases are clinically undistinguishable with the exception of the presence of some kind of family history of the disease in relatives,3 some seemingly sporadic cases could be of familial origin. Examples of situations where absence of family history may lead one to falsely conclude that the case is sporadic, includes very small families, instances where the patient is not aware of the health status of their relatives, or if some family …

A novel PLP1 mutation further expands the clinical heterogeneity at the locus.

Abstract: Objectif: Le but de l'etude etait de caracteriser au niveau clinique et moleculaire une famille atteinte de paraplegie spastique hereditaire (PSH). Contexte: Les PSH constituent un groupe de maladies neurodegeneratives heterogenes au point de vue genetique qui se caracterisent par des signes d'atteinte progressive du neurone moteur superieur. Des mutations du gene de la proteine proteolipide (PLP1) ont ete identifiees dans des familles chez qui la maladie etait liee au locus du gene de la paraplegie spastique liee au chromosome X, SPG2, situe en Xq22. Cependant, la maladie de Pelizaeus-Merzbacher (MPM) est egalement une maladie neurologique liee au chromosome X et causee par des mutations du gene PLP1. Methode: Nous avons examine le locus du gene SPG2 par analyse de liaison dans cette famille. Le gene de la PLP1 a ete sequence. Nous presentons les observations faites dans une grande famille canadienne-francaise atteinte de PSH liee au chromosome X. Le cas index a consulte en bas âge parce qu'il presentait un retard de developpement et une paraplegie spastique progressive. Il est en fauteuil roulant depuis l'âge de trois ans. Au moment du dernier examen de suivi, il avait 20 ans et presentait une spasticite severe touchant surtout les membres inferieurs, une dysfonction cerebelleuse moderee et une atrophie optique. Resultats: Nous avons constate que la maladie etait liee au locus SPG2 et identifie une mutation G → A (M1R) dans le codon d'initiation du gene de PLP1, ce qui donne vraisemblablement lieu a une absence complete de la proteine proteolipide. Conclusions: Nous rapportons une nouvelle mutation du gene de la PLP1 chez un patient presentant un phenotype clinique compatible avec une absence totale de la proteine.

CYP7B1 mutations in French-Canadian hereditary spastic paraplegia subjects.

Abstract: Lorrain disease, refers to progressive motor neurodegenerative disorders characterized by lower limb spasticity and weakness. This group of diseases has been shown to include very heterogeneous clinical manifestation and various modes of inheritance (dominant, recessive and X-linked) have been reported. Hereditary spastic paraplegia are classified as pure or complicated forms. Cases with pure forms only present lower limb spasticity but complicated forms have additional neurological features such as cerebellar ataxia, intellectual disabilities, dementia, thin corpus callosum, and/or visual dysfunction. To date, over 48 spastic paraplegia loci including 20 genes have been identified. In 1994, one of these loci, SPG5A, was mapped to chromosome 8q21.3 and deemed to contain a gene underlying a pure-autosomal recessive form of HSP (MIM#270800)1. Many HSP families have been mapped to this particular locus and the causative gene was finally identified in 2008. Mutations in Cytochrome P450, family 7, subfamily B polypeptide 1 (CYP7B1) gene were then found to underlie this particular disorder; homozygous mutations were originally identified in a consanguineous English family2. CYP7B1 extends over ~220 Kb gene and contain six exons that encode for an evolutionarily conserved steroid metabolizing enzyme, cytochrome P450. This particular enzyme is widely expressed in many tissues, with the highest mRNA levels found in the liver and the brain. Containing 506 amino-acid, this enzyme catalyzes the 6α-7α hydroxylation of several endogenous substrates such as: dehydroepiandrosterone, pregnenolone, oxysterols, 25-and 27-hydroxycholestrol. In the liver, CYP7B1 is implicated in the synthesis of bile salt that regulate bile flow and indirectly the excretion of metabolites (e.g. porphyrins arising from heme breakdown). Interestingly, mutations in the CYP7B1 gene are also known to cause liver failure in children. Additional roles for CYP7B1 were described in the metabolism of oestrogen receptor ligands and in immunoglobulin production3. The exact role of CYP7B1 in the brain is unknown, other than its link to HSP. The main goal of our study was to determine if CYP7B1 mutations could explain disease in some of our HSP patients.

Letter to the editors: comment on "hereditary sensory and autonomic neuropathy II due to novel mutation in the HSN2 gene in Mexican families"

Abstract: In the April 6, 2011 issue of Journal of Neurology, Pacheco-Cuellar et al. [1] reported the finding of an eightnucleotide deletion (c.1219_1226 delTCTCAGCA, NM 213655 and NM 001184985), which causes a frame-shift mutation in the HSN2 coding sequence, of patients from two Mexican families, segregating cases of hereditary sensory neuropathy type II (HSAN II, OMIM 201300). This report revealed a previously unreported mutation, which will affect the WNK1/HSN2 isoforms of WNK1 and not only the HSN2 coding region, and so we believe it has been presented in a confusing manner for readers who may not be aware that the HSN2 region is in fact an exon of WNK1. Hence, we believe these authors greatly misinterpreted our earlier findings about the structure of WNK1 and its relation with the HSN2 coding region [2]. The current title is misleading as HSN2 is designated as a gene rather than a coding exon of WNK1, something that was proposed in our original (2004) report on HSAN II as it was presumed that ‘‘HSN2 consists of a single exon located within intron 8 of the PRKWNK1 gene and is transcribed from the same strand’’ [3]. However, our group subsequently (2008) established that ‘‘HSN2 is as an alternatively spliced exon of WNK1’’, and that ‘‘HSN2 is part of the WNK1 mRNA, making it an unreported and novel nervous system–specific disease-causing isoform of WNK1 (WNK1/HSN2)’’ [2]. Furthermore, our work, as well as that of others, showed the full length WNK1 protein to migrate at *250 kDa on Western blots prepared using mouse and human tissues [2, 4]. More specifically, we reported that ‘‘the anti-WNK1 antibody failed to reveal any band at approximately 230 kDa in which WNK1/HSN2 was detected with the anti-HSN2 antiserum’’; also, that ‘‘this lower M.W. of WNK1/HSN2 is likely attributable to the use of the second promoter (P2) of WNK1 [5]’’ [2]. In their report, Pacheco-Cuellar et al. concluded that a 416-amino acid protein came from the deletion of eight nucleotides (c. 1219_1226 delTCTCAGCA) and led to the use of a novel stop codon 26 nucleotides after the presumed stop codon of HSN2; the predicted M.W. of a 416-amino acid protein would be much lower than the one of WNK1/ HSN2. While this novel mutation is likely genuine it is considered in an inadequate coding context, as it is not referring to the stop codon of WNK1 and it is referring to the ORF of HSN2 reported in 2004; hence, the mutation described by these authors will actually produce a truncated WNK1 protein lacking the downstream WNK1 exons. Their misinterpretation of the structure of WNK1 and its encoding HSN2 exon, as described in our 2008 report [2], is obvious when considering the authors cited the protein M. Shekarabi P. A. Dion G. A. Rouleau (&) Center of Excellence in Neuroscience of the Université de Montréal (CENUM), Centre de Recherche du Centre Hospitalier de l’Université de Montréal (CRCHUM), University of Montreal, 1560, rue Sherbrooke East, De-Sève Pavillon, room Y-3616-2, Montreal, QC H2L 4MI, Canada e-mail: guy.rouleau@umontreal.ca