Establishing an online resource to facilitate global collaboration and inclusion of underrepresented populations: Experience from the MJFF Global Genetic Parkinson's Disease Project.

Parkinson's disease (PD) is the fastest-growing neurodegenerative disorder, currently affecting ~7 million people worldwide. PD is clinically and genetically heterogeneous, with at least 10% of all cases explained by a monogenic cause or strong genetic risk factor. However, the vast majority of our present data on monogenic PD is based on the investigation of patients of European White ancestry, leaving a large knowledge gap on monogenic PD in underrepresented populations. Gene-targeted therapies are being developed at a fast pace and have started entering clinical trials. In light of these developments, building a global network of centers working on monogenic PD, fostering collaborative research, and establishing a clinical trial-ready cohort is imperative. Based on a systematic review of the English literature on monogenic PD and a successful team science approach, we have built up a network of 59 sites worldwide and have collected information on the availability of data, biomaterials, and facilities. To enable access to this resource and to foster collaboration across centers, as well as between academia and industry, we have developed an interactive map and online tool allowing for a quick overview of available resources, along with an option to filter for specific items of interest. This initiative is currently being merged with the Global Parkinson's Genetics Program (GP2), which will attract additional centers with a focus on underrepresented sites. This growing resource and tool will facilitate collaborative research and impact the development and testing of new therapies for monogenic and potentially for idiopathic PD patients.

Association of BglII Polymorphism in ITGA2 and (894G/T and -786T/C) Polymorphisms in eNOS Gene With Stroke Susceptibility in Tunisian Patients α2 Gene Polymorphism in α2ß1 Integrin and eNOS Gene Variants and Stroke.

BACKGROUND: This study investigated the association of BglII polymorphism in α2ß1 integrin gene (ITGA2) and eNOS (894G/T and -786T/C) polymorphisms with ischemic stroke (IS) in Tunisian patients. METHODS: The study comprised 210 patients with IS and 208 controls. The genotypes of the BglII polymorphism in ITGA2 and eNOS (894G/T and -786T/C) polymorphisms were determined using the PCR-RFLP. The χ2 test was used and the genotype data comparison included heterozygous groups. Haplotype estimation and multiple logistic regression analysis were performed to analyze the significance of polymorphisms. RESULTS: The genotype distribution of the BglII polymorphism was significantly different between cases and controls (p < 0.004). This polymorphism was associated with the risk of IS (OR = 3.38, p < 0.001) for the BglII(+/+) genotype. Likewise, the genotype distributions of eNOS (894G/T and -786T/C) polymorphisms were significantly different between the two groups (p < 0.005 and p < 0.01, respectively). The 894G/T polymorphism increased the risk of IS for the TT genotype (OR = 2.23, p < 0.008) and the GT genotype (OR = 1.74, p < 0.009). In addition, the -786T/C variant in the eNOS gene was a risk factor for IS for CC homozygous (OR = 2.52, p < 0.005). T-C Haplotype (OR = 3.06) from combination of the eNOS (894G/T and -786T/C) and T-C-BglII(+) haplotype (OR = 2.76) from combination of eNOS and ITGA2 polymorphisms represented high risks for IS. CONCLUSIONS: This study suggests that the BglII variant in ITGA2 is associated with IS susceptibility. Furthermore, the 894G/T and -786T/C polymorphisms in the eNOS gene may be considered as genetic risk factors for IS in the Tunisian population.

Bi-allelic variants in RNF170 are associated with hereditary spastic paraplegia.

Alterations of Ca2+ homeostasis have been implicated in a wide range of neurodegenerative diseases. Ca2+ efflux from the endoplasmic reticulum into the cytoplasm is controlled by binding of inositol 1,4,5-trisphosphate to its receptor. Activated inositol 1,4,5-trisphosphate receptors are then rapidly degraded by the endoplasmic reticulum-associated degradation pathway. Mutations in genes encoding the neuronal isoform of the inositol 1,4,5-trisphosphate receptor (ITPR1) and genes involved in inositol 1,4,5-trisphosphate receptor degradation (ERLIN1, ERLIN2) are known to cause hereditary spastic paraplegia (HSP) and cerebellar ataxia. We provide evidence that mutations in the ubiquitin E3 ligase gene RNF170, which targets inositol 1,4,5-trisphosphate receptors for degradation, are the likely cause of autosomal recessive HSP in four unrelated families and functionally evaluate the consequences of mutations in patient fibroblasts, mutant SH-SY5Y cells and by gene knockdown in zebrafish. Our findings highlight inositol 1,4,5-trisphosphate signaling as a candidate key pathway for hereditary spastic paraplegias and cerebellar ataxias and thus prioritize this pathway for therapeutic interventions.

Stroke in the Middle-East and North Africa: A 2-year prospective observational study of stroke characteristics in the region-Results from the Safe Implementation of Treatments in Stroke (SITS)-Middle-East and North African (MENA).

BACKGROUND AND METHODS: Stroke incidence and mortality are reported to have increased in the Middle-East and North African (MENA) countries during the last decade. This was a prospective observational study to examine the baseline characteristics of stroke patients in the MENA region and to compare the MENA vs. the non-MENA stroke cohort in the Safe Implementation of Treatments in Stroke (SITS) International Registry. RESULTS: Of the 13,822 patients with ischemic and hemorrhagic stroke enrolled in the SITS-All Patients Protocol between June 2014 and May 2016, 5897 patients (43%) were recruited in MENA. The median onset-to-door time was 5 h (IQR: 2:20-13:00), National Institutes of Health Stroke Scale (NIHSS) score was 8 (4-13) and age was 65 years (56-76). Hypertension (66%) and diabetes (38%) were the prevailing risk factors; large artery stenosis > 50% (25.3%) and lacunar strokes (24.1%) were the most common ischemic stroke etiologies. In comparison, non-MENA countries displayed an onset-to-door time of 5:50 h (2:00-18:45), a median of NIHSS 6 (3-14), and a median age of 66 (56-76), with other large vessel disease and cardiac embolism as the main ischemic stroke etiologies. Hemorrhagic strokes (10%) were less common compared to non-MENA countries (13.9%). In MENA, only a low proportion of patients (21%) was admitted to stroke units. CONCLUSIONS: MENA patients are slightly younger, have a higher prevalence of diabetes and slightly more severe ischemic strokes, commonly of atherosclerotic or microvascular etiology. Admission into stroke units and long-term follow-up need to be improved. It is suspected that cardiac embolism and atrial fibrillation are currently underdiagnosed in MENA countries.

Disability progression in multiple sclerosis: a Tunisian prospective cohort study.

Data regarding multiple sclerosis (MS) course in North Africans are scarce and mainly retrospective. To prospectively assess disability progression of multiple sclerosis in Tunisia. Analysis was performed in 600 patients from the MS database of the Mongi Ben Hmida National Institute of Neurology (Tunis, Tunisia), prospectively recorded over a 10-year period. Two MS phases were defined: phase 1, from MS clinical onset to Disability Status Scale (DSS) 3; and phase 2, from DSS 3 to DSS 6. Median durations of both phases and median ages at DSS 3 and DSS 6 were estimated using the Kaplan-Meier method. Median ages at DSS scores 3 and 6 were 48 years (95% confidence interval (CI), 45-50) and 53 years (95% CI, 52-55), respectively. Median time from onset to DSS 3 (phase 1 duration) was 9 years (95% CI, 7-11) and median time to DSS 6 was 12 years (95% CI, 10-15). Median phase 2 duration was 3 years (95% CI, 2.4-3.6). Males and progressive-onset patients had faster disability worsening during the first phase of the disease. Conversely, disability progression during the second phase was independent of gender and MS phenotype at onset. Our study showed that disability progression followed a two-stage process in Tunisian MS patients with however a more aggressive course compared to that in Westerners.

SLC25A46 Mutations Associated with Autosomal Recessive Cerebellar Ataxia in North African Families.

BACKGROUND: Autosomal recessive cerebellar ataxias (ARCA) are a complex group of neurodegenerative disorders with high clinical and genetic heterogeneity. In most cases, the cerebellar ataxia is not pure, and complicating clinical features such as pyramidal signs or extraneurological features are found. OBJECTIVE: To identify the genetic origin of the cerebellar ataxia for 3 consanguineous North African families presenting with ARCA. METHODS: Genome-wide high-density SNP genotyping and whole-exome sequencing were performed followed by Sanger sequencing for mutation confirmation. RESULTS: Two variants were identified in SLC25A46. Mutations in this gene have been previously associated with Charcot-Marie-Tooth type 2 and optic atrophy. While the previously reported variant p.Arg340Cys seems to be consistently associated with the same clinical features such as childhood onset, optic atrophy, gait and speech difficulties, and wasting of the lower limbs, the patient with the novel mutation p.Trp160Ser did not present with optic atrophy and his ocular abnormalities were limited to nystagmus and saccadic pursuit. CONCLUSION: In this study, we report a novel variant (p.Trp160Ser) in SLC25A46 and we broaden the phenotypic spectrum associated with mutations in SLC25A46.

Cerebral Venous Thrombosis: A Tunisian Monocenter Study on 160 Patients.

OBJECTIVE: Data regarding cerebral venous thrombosis in North Africa are scarce. This study aims to identify the clinical features, risk factors, outcome, and prognosis of cerebral venous thrombosis in Tunisia. METHODS: Data of 160 patients with radiologically confirmed cerebral venous thrombosis, hospitalized in Mongi Ben Hmida National Institute of Neurology (Tunis, Tunisia), were retrospectively collected and analyzed. RESULTS: The mean age was 37.3 years with a female predominance (83.1%). The mode of onset was subacute in most cases (56.2%). Headache was the most common symptom (71.3%), and focal neurologic symptoms were the main clinical presentation (41.8%). The most common sites of thrombosis were the superior sagittal sinus (65%) and the lateral sinus (60.6%). More than 1 sinus was involved in 114 (71.2%) patients. Parenchymal lesions observed in 85 (53.1%) patients did not correlate with cerebral venous thrombosis extent. Major risk factors were obstetric causes (pregnancy and puerperium) found in 46 (38.6% of women aged <50 years) patients, followed by anemia (28.1%) and congenital or acquired thrombophilia (16.2%). Mortality rate was of 6.6%. Good outcome at 6 months (modified Rankin Scale ≤2) was observed in 105 (87.5%)of 120 patients available for follow-up. Predictors of poor outcome were altered consciousness and elevated plasma C-reactive protein levels. CONCLUSION: Clinical and radiologic presentation of cerebral venous thrombosis in Tunisia was quite similar to other parts of the world with, however, a particularly high frequency of obstetric causes. Plasma C-reactive protein level should be considered as a prognostic factor in CVT.

Progressive cerebellar degeneration revealing Primary Sjögren Syndrome: a case report.

BACKGROUND: Cerebellar ataxia represents a rare and severe complication of SjÓ§gren syndrome (SS), especially with a progressive onset and cerebellar atrophy on imaging. CASE PRESENTATION: We report the case of a 30-year-old woman, with a past history of dry eyes and mouth, who presented a severe cerebellar ataxia worsening over 4 years associated with tremor of the limbs and the head. Brain MRI showed bilateral hyperintensities on T2 and FLAIR sequences, affecting periventricular white matter, with marked cerebellar atrophy. Complementary investigations confirmed the diagnosis of primary SS (pSS). The patient was treated by methylprednisolone, Cyclophosphamid and Azathioprine. Her clinical and radiological states are stabilized after 2 years of following. Primary cerebellar degeneration is extremely rarely associated with pSS. Few cases of isolated cerebellar ataxia or belonging to a multifocal disease were reported in the literature, most of them characterized by an acute or rapidly progressive onset. Cerebellar atrophy was described in only three patients. There have been few clarifications of the pathogenesis of the neurological manifestations in pSS. Treatment is based on corticosteroids and immunosuppressive agents with no consensus of a specific therapy. CONCLUSIONS: Cerebellar ataxia due to pSS may exceptionally mimic a degenerative cerebellar ataxia, especially when the onset is progressive, which represents the particularity of our observation. The role of brain MRI and antibodies remains important for the differential diagnosis.

DNM3 and genetic modifiers of age of onset in LRRK2 Gly2019Ser parkinsonism: a genome-wide linkage and association study.

BACKGROUND: Leucine-rich repeat kinase 2 (LRRK2) mutation 6055G→A (Gly2019Ser) accounts for roughly 1% of patients with Parkinson's disease in white populations, 13-30% in Ashkenazi Jewish populations, and 30-40% in North African Arab-Berber populations, although age of onset is variable. Some carriers have early-onset parkinsonism, whereas others remain asymptomatic despite advanced age. We aimed to use a genome-wide approach to identify genetic variability that directly affects LRRK2 Gly2019Ser penetrance. METHODS: Between 2006 and 2012, we recruited Arab-Berber patients with Parkinson's disease and their family members (aged 18 years or older) at the Mongi Ben Hamida National Institute of Neurology (Tunis, Tunisia). Patients with Parkinson's disease were diagnosed by movement disorder specialists in accordance with the UK Parkinson's Disease Society Brain Bank criteria, without exclusion of familial parkinsonism. LRRK2 carrier status was confirmed by Sanger sequencing or TaqMan SNP assays-on-demand. We did genome-wide linkage analysis using data from multi-incident Arab-Berber families with Parkinson's disease and LRRK2 Gly2019Ser (with both affected and unaffected family members). We assessed Parkinson's disease age of onset both as a categorical variable (dichotomised by median onset) and as a quantitative trait. We used data from another cohort of unrelated Tunisian LRRK2 Gly2019Ser carriers for subsequent locus-specific genotyping and association analyses. Whole-genome sequencing in a subset of 14 unrelated Arab-Berber individuals who were LRRK2 Gly2019Ser carriers (seven with early-onset disease and seven elderly unaffected individuals) subsequently informed imputation and haplotype analyses. We replicated the findings in separate series of LRRK2 Gly2019Ser carriers originating from Algeria, France, Norway, and North America. We also investigated associations between genotype, gene, and protein expression in human striatal tissues and murine LRRK2 Gly2019Ser cortical neurons. FINDINGS: Using data from 41 multi-incident Arab-Berber families with Parkinson's disease and LRRK2 Gly2019Ser (150 patients and 103 unaffected family members), we identified significant linkage on chromosome 1q23.3 to 1q24.3 (non-parametric logarithm of odds score 2·9, model-based logarithm of odds score 4·99, θ=0 at D1S2768). In a cohort of unrelated Arab-Berber LRRK2 Gly2019Ser carriers, subsequent association mapping within the linkage region suggested genetic variability within DNM3 as an age-of-onset modifier of disease (n=232; rs2421947; haplotype p=1·07 × 10-7). We found that DNM3 rs2421947 was a haplotype tag for which the median onset of LRRK2 parkinsonism in GG carriers was 12·5 years younger than that of CC carriers (Arab-Berber cohort, hazard ratio [HR] 1·89, 95% CI 1·20-2·98). Replication analyses in separate series from Algeria, France, Norway, and North America (n=263) supported this finding (meta-analysis HR 1·61, 95% CI 1·15-2·27, p=0·02). In human striatum, DNM3 expression varied as a function of rs2421947 genotype, and dynamin-3 localisation was perturbed in murine LRRK2 Gly2019Ser cortical neurons. INTERPRETATION: Genetic variability in DNM3 modifies age of onset for LRRK2 Gly2019Ser parkinsonism and informs disease-relevant translational neuroscience. Our results could be useful in genetic counselling for carriers of this mutation and in clinical trial design. FUNDING: The Canada Excellence Research Chairs (CERC), Leading Edge Endowment Fund (LEEF), Don Rix BC Leadership Chair in Genetic Medicine, National Institute on Aging, National Institute of Neurological Disorders and Stroke, the Michael J Fox Foundation, Mayo Foundation, the Roger de Spoelberch Foundation, and GlaxoSmithKline.

Defects in the CAPN1 Gene Result in Alterations in Cerebellar Development and Cerebellar Ataxia in Mice and Humans.

A CAPN1 missense mutation in Parson Russell Terrier dogs is associated with spinocerebellar ataxia. We now report that homozygous or heterozygous CAPN1-null mutations in humans result in cerebellar ataxia and limb spasticity in four independent pedigrees. Calpain-1 knockout (KO) mice also exhibit a mild form of ataxia due to abnormal cerebellar development, including enhanced neuronal apoptosis, decreased number of cerebellar granule cells, and altered synaptic transmission. Enhanced apoptosis is due to absence of calpain-1-mediated cleavage of PH domain and leucine-rich repeat protein phosphatase 1 (PHLPP1), which results in inhibition of the Akt pro-survival pathway in developing granule cells. Injection of neonatal mice with the indirect Akt activator, bisperoxovanadium, or crossing calpain-1 KO mice with PHLPP1 KO mice prevented increased postnatal cerebellar granule cell apoptosis and restored granule cell density and motor coordination in adult mice. Thus, mutations in CAPN1 are an additional cause of ataxia in mammals, including humans.

Motor phenotype of LRRK2-associated Parkinson's disease: a Tunisian longitudinal study.

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) were found to be a significant cause of late-onset autosomal dominant forms of Parkinson's disease (PD). To determine the motor characteristics of LRRK2-related disease, we conducted a longitudinal study of 58 G2019S LRRK2-associated PD patients and compared them with genetically undefined (GU) PD patients. Fifty-eight patients diagnosed with PD-related LRRK2 G2019S mutation were included in the study and compared with 54 sporadic PD patients with negative tests for LRRK2 G2019S, PINK1, SNCA, PRKN, and DJ1 mutations. Patients were assessed at baseline and after a follow-up period of 6 years. The Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), the Hoehn and Yahr, and the Schwab and England scores were determined. Logistic regression was used to examine associations of G2019S mutation status with motor phenotype and rate of motor decline. The LRRK2-associated PD patients had a mean age of onset of 56.25 ± 12.05 years and in most cases (58.6%) a postural instability gait difficulty (PIGD) phenotype. The mean annual decline in the MDS-UDRS III motor score and the Hoehn and Yahr staging was of 1.3% and 2%, respectively. The PIGD phenotype predicted a more rapid progression of motor impairment. The PD motor phenotype and motor scores were similar in the LRRK2-associated PD group and in the GU PD group, with no significant differences in the progression rate of motor impairment. Motor phenotype seems to be similar in LRRK2-related PD and idiopathic PD.

Pseudotumoral brain lesion as the presenting feature of primary Sjögren's syndrome.

BACKGROUND: The frequency and type of central nervous system involvement in primary Sjögren's syndrome (pSS) remain controversial. Brain magnetic resonance imaging (MRI) abnormalities in pSS are usually discrete hyperintense areas in the white matter. Tumefactive brain lesions have been rarely reported. CASE REPORT: We describe a 31-year-old woman who exhibited transcortical motor aphasia, hemiparesis and partial motor seizures as the initial manifestation of pSS. Brain MRI revealed a large frontoparietal lesion extending into the corpus callosum. The patient had spontaneous recovery and developed sicca symptoms 6 months after onset. Primary SS was diagnosed on the basis of clinical features, abnormal Schirmer test findings, high levels of anti-La/SSB antibodies and positive salivary gland biopsy results. CONCLUSION: The present case suggests that a pseudotumoral brain lesion can occur as an initial symptom of pSS.

DNAJC13 mutations in Parkinson disease.

A Saskatchewan multi-incident family was clinically characterized with Parkinson disease (PD) and Lewy body pathology. PD segregates as an autosomal-dominant trait, which could not be ascribed to any known mutation. DNA from three affected members was subjected to exome sequencing. Genome alignment, variant annotation and comparative analyses were used to identify shared coding mutations. Sanger sequencing was performed within the extended family and ethnically matched controls. Subsequent genotyping was performed in a multi-ethnic case-control series consisting of 2928 patients and 2676 control subjects from Canada, Norway, Taiwan, Tunisia, and the USA. A novel mutation in receptor-mediated endocytosis 8/RME-8 (DNAJC13 p.Asn855Ser) was found to segregate with disease. Screening of cases and controls identified four additional patients with the mutation, of which two had familial parkinsonism. All carriers shared an ancestral DNAJC13 p.Asn855Ser haplotype and claimed Dutch-German-Russian Mennonite heritage. DNAJC13 regulates the dynamics of clathrin coats on early endosomes. Cellular analysis shows that the mutation confers a toxic gain-of-function and impairs endosomal transport. DNAJC13 immunoreactivity was also noted within Lewy body inclusions. In late-onset disease which is most reminiscent of idiopathic PD subtle deficits in endosomal receptor-sorting/recycling are highlighted by the discovery of pathogenic mutations VPS35, LRRK2 and now DNAJC13. With this latest discovery, and from a neuronal perspective, a temporal and functional ecology is emerging that connects synaptic exo- and endocytosis, vesicular trafficking, endosomal recycling and the endo-lysosomal degradative pathway. Molecular deficits in these processes are genetically linked to the phenotypic spectrum of parkinsonism associated with Lewy body pathology.

Molecular, clinical and peripheral neuropathy study of Tunisian patients with ataxia with vitamin E deficiency.

Ataxia with vitamin E deficiency is an autosomal recessive cerebellar ataxia caused by mutations in the α-tocopherol transfer protein coding gene localized on chromosome 8q, leading to lower levels of serum vitamin E. More than 91 patients diagnosed with ataxia with vitamin E deficiency have been reported worldwide. The majority of cases originated in the Mediterranean region, and the 744delA was the most common mutation among the 22 mutants previously described. We examined the clinical and molecular features of a large cohort of 132 Tunisian patients affected with ataxia with vitamin E deficiency. Of these patients, nerve conduction studies were performed on 45, and nerve biopsy was performed on 13. Serum vitamin E was dramatically reduced for 105 of the patients analysed. Molecular analysis revealed that 91.7% of the patients (n = 121) were homozygous for the 744delA mutation. Three other mutations were detected among the remaining patients (8.3%, n = 11) in the homozygous state. Two were previously reported (400C>T and 205-1G>T), and one was novel (553+1T>A). Age of onset was 13.2 ± 5.9 years, with extremes of 2 and 37 years. All described patients exhibited persistent progressive cerebellar ataxia with generally absent tendon reflexes. Deep sensory disturbances, pyramidal syndrome and skeletal deformities were frequent. Head tremor was present in 40% of the patients. Absence of neuropathy or mild peripheral neuropathy was noted in more than half of the cohort. This is the largest study of the genetic, clinical and peripheral neuropathic characteristics in patients with ataxia and vitamin E deficiency. The 744delA mutation represents the most common pathological mutation in Tunisia and worldwide, likely because of a Mediterranean founder effect. Our study led us to suggest that any patient displaying an autosomal recessive cerebellar ataxia phenotype with absent tendon reflexes and minor nerve abnormalities should first be screened for the 744delA mutation, even in the absence of a serum vitamin E measurement.

Clinical features and molecular genetics of two Tunisian families with abetalipoproteinemia.

Abetalipoproteinemia (ABL) is a rare monogenic disease characterized by very low plasma levels of cholesterol and triglyceride and almost complete absence of apolipoprotein B (apoB)-containing lipoproteins. Typically, patients present with failure to thrive, acanthocytosis, pigmented retinopathy and neurological features. It has been shown that ABL results from mutations in the gene encoding the microsomal triglyceride transfer protein (MTTP). Sanger sequencing of MTTP was performed for two unrelated consanguineous Tunisian families with two affected individuals each, presenting a more severe ABL phenotype than previously reported in the literature. The patients were found to be homozygous for two novel mutations. In the first family, a nonsense mutation, c.2313T>A, leading to a truncated protein (p.Y771X) was identified. In the second family, a splice mutation, IVS 9+2T>G, was found. These mutations are believed to abolish the assembly and secretion of apoB-containing lipoproteins.

Giant axonal neuropathy.

Giant axonal neuropathy (GAN) is a rare hereditary autosomal recessive neurodegenerative disease affecting both the peripheral and the central nervous system. Clinically it is characterized by an age of onset during the first decade, progressive and severe motor sensory neuropathy followed, in some patients, by the occurrence of various central nervous system signs such as cerebellar syndrome, upper motor neuron signs, or epilepsy. Although kinky hairs are reported in the majority of patients, it is not a constant finding. The prognosis is usually severe with death occurring during the second or third decade; nevertheless a less severe course is reported in some patients. The presence of a variable number of giant axons filled with neurofilaments in the nerve biopsy represents the pathological feature of the disease and it is usually associated to a variable degree with axonal loss and demyelization. Giant axons are also found in the central nervous system associated with Rosenthal fibers and a variable degree of involvement of white matter and neuronal loss. The disease is caused by mutation in the GAN gene encoding for gigaxonin, a member of BTB-Kelch. Up to now 37 mutations in the GAN gene have been reported. These mutations are scattered over the 11 exons of the gene without a clear genotype-phenotype correlation. These mutations resulting in gigaxonin deficiency lead to a slow down in ubiquitin-mediated protein degradation and possibly of other unidentified proteins. GAN represents a good model of a neurodegenerative disorder in which there is a primary defect of the ubiquitin proteasome system and its network with neurofilaments. The clarification of molecular mechanisms involved in GAN can help in understanding other frequent neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson disease.

STX6 rs1411478 is not associated with increased risk of Parkinson's disease.

A variant in Syntaxin 6 (a soluble N-ethylmaleimide-sensitive factor attachment protein receptor STX6) (rs1411478) has been shown to be associated with progressive supranuclear palsy (PSP). Although Parkinson's disease (PD) and PSP are distinct neurodegenerative diseases, they share some clinical and genetic features. In this study, we evaluated STX6 genetic variability in PD susceptibility in ethnically matched case-control series from Canada, Norway, Taiwan and Tunisia and we evaluated the presence of pathogenic mutations within families. No pathogenic mutations were found in STX6. Similarly, statistical analysis of rs1411478 failed to identify differences in genotype or allelic frequencies between cases and controls. Our results do not support a role for STX6 in PD.

Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.

Autosomal-recessive cerebellar ataxia (ARCA) comprises a large and heterogeneous group of neurodegenerative disorders with more than 20 different forms currently recognized, many of which are also associated with increased tone and some of which have limb spasticity. Gaucher disease is a lysosomal storage disease resulting from a defect in the enzyme acid ß-glucosidase 1. ß-glucosidase 2 is an enzyme with similar glucosylceramidase activity but to date has not been associated with a monogenic disorder. We studied four unrelated consanguineous families of Tunisian decent diagnosed with cerebellar ataxia of unknown origin. We performed homozygosity mapping and whole-exome sequencing in an attempt to identify the genetic origin of their disorder. We were able to identify mutations responsible for autosomal-recessive ataxia in these families within the gene encoding ß-glucosidase 2, GBA2. Two nonsense mutations (c.363C>A [p.Tyr121(∗)] and c.1018C>T [p.Arg340(∗)]) and a substitution (c.2618G>A [p.Arg873His]) were identified, probably resulting in nonfunctional enzyme. This study suggests GBA2 mutations are a cause of recessive spastic ataxia and responsible for a form of glucosylceramide storage disease in humans.