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The G4C2-repeat expansion in C9orf72 is the most common cause of frontotemporal dementia and of amyotrophic lateral sclerosis. The variability of age at onset and phenotypic presentations is a hallmark of C9orf72 disease. In this study, we aimed to identify modifying factors of disease onset in C9orf72 carriers using a family-based approach, in pairs of C9orf72 carrier relatives with concordant or discordant age at onset. Linkage and association analyses provided converging evidence for a locus on chromosome Xq27.3. The minor allele A of rs1009776 was associated with an earlier onset (P = 1 × 10-5). The association with onset of dementia was replicated in an independent cohort of unrelated C9orf72 patients (P = 0.009). The protective major allele delayed the onset of dementia from 5 to 13 years on average depending on the cohort considered. The same trend was observed in an independent cohort of C9orf72 patients with extreme deviation of the age at onset (P = 0.055). No association of rs1009776 was detected in GRN patients, suggesting that the effect of rs1009776 was restricted to the onset of dementia due to C9orf72. The minor allele A is associated with a higher SLITRK2 expression based on both expression quantitative trait loci (eQTL) databases and in-house expression studies performed on C9orf72 brain tissues. SLITRK2 encodes for a post-synaptic adhesion protein. We further show that synaptic vesicle glycoprotein 2 and synaptophysin, two synaptic vesicle proteins, were decreased in frontal cortex of C9orf72 patients carrying the minor allele. Upregulation of SLITRK2 might be associated with synaptic dysfunctions and drives adverse effects in C9orf72 patients that could be modulated in those carrying the protective allele. How the modulation of SLITRK2 expression affects synaptic functions and influences the disease onset of dementia in C9orf72 carriers will require further investigations. In summary, this study describes an original approach to detect modifier g

A (GGGGCC) n repeat expansion in C9orf72 gene is the major cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The relations between the repeats size and the age at disease onset (AO) or the clinical phenotype (FTD vs. ALS) were investigated in 125 FTD, ALS, and presymptomatic carriers. Positive correlations were found between repeats number and the AO (p < 10 e−4 ) but our results suggested that the association was mainly driven by age at collection (p < 10 e−4 ). A weaker association was observed with clinical presentation (p = 0.02), which became nonsignificant after adjustment for the age at collection in each group. Importantly, repeats number variably expanded or contracted over time in carriers with multiple blood samples, as well as through generations in parent-offspring pairs, conversely to what occurs in several expansion diseases with anticipation at the molecular level. Finally, this study establishes that measure of repeats number in lymphocytes is not a reliable biomarker predictive of the AO or disease outcome in C9orf72 long expansion carriers.

OBJECTIVES: We describe the largest series of patients with TARDBP mutations presenting with frontotemporal dementia (FTD) and review the cases in the literature to precisely characterize FTD diseases associated with this genotype. METHODS: The phenotypic characteristics of 29 TARDBP patients, including 10 new French and Dutch cases and 19 reviewed from the literature, were evaluated. RESULTS: The most frequent phenotype was a behavioral variant frontotemporal dementia (bvFTD), but a significant proportion (40%) of our patients had semantic (svFTD) or nonfluent variants (nfvFTD) at onset; and svFTD was significantly more frequent in TARDBP carriers than in other FTD genotypes (p < 0.001). Remarkably, only a minority (40%) of our patients secondarily developed amyotrophic lateral sclerosis (ALS). Two patients carried a homozygous mutation but strikingly different phenotypes (bvFTD and ALS) indicating that homozygosity does not result in a specific phenotype. Earlier age at onset in children than parent's generations, mimicking an apparent "anticipation" (21.8 ± 9.3 years, p = 0.001), and possible reduced penetrance were present in most families. CONCLUSIONS: This study enlarges the phenotypic spectrum of TARDBP and will have important clinical implications: (1) FTD can be the only clinical manifestation of TARDBP mutations; (2) Initial language or semantic disorders might be indicative of a specific genotype; (3) Mutations should be searched in all FTD phenotypes after exclusion of major genes, even in the absence of ALS in the proband or in family history; (4) reduced penetrance and clinical variability should be considered to deliver appropriate genetic counseling.

TMEM106B was identified as a risk factor for frontotemporal lobar degeneration (FTD) with TAR DNA-binding protein 43 kDa inclusions. It has been reported that variants in this gene are genetic modifiers of the disease and that this association is stronger in patients carrying a GRN mutation or a pathogenic expansion in chromosome 9 open reading frame 72 (C9orf72) gene. Here, we investigated the contribution of TMEM106B polymorphisms in cohorts of FTD and FTD with amyotrophic lateral sclerosis patients from France and Italy. Patients carrying the C9orf72 expansion (n = 145) and patients with GRN mutations (n = 76) were compared with a group of FTD patients (n = 384) negative for mutations and to a group of healthy controls (n = 552). In our cohorts, the presence of the C9orf72 expansion did not correlate with TMEM106B genotypes but the association was very strong in individuals with pathogenic GRN mutations (p = 9.54 × 10(-6)). Our data suggest that TMEM106B genotypes differ in FTD patient cohorts and strengthen the protective role of TMEM106B in GRN carriers. Further studies are needed to determine whether TMEM106B polymorphisms are associated with other genetic causes for FTD, including C9orf72 repeat expansions.

Contains fulltext : 80171.pdf (publisher's version ) (Closed access), In order to identify new metabolic abnormalities in patients with complex neurodegenerative disorders of unknown aetiology, we performed high resolution in vitro proton nuclear magnetic resonance spectroscopy on patient cerebrospinal fluid (CSF) samples. We identified five adult patients, including two sisters, with significantly elevated free sialic acid in the CSF compared to both the cohort of patients with diseases of unknown aetiology (n = 144; P < 0.001) and a control group of patients with well-defined diseases (n = 91; P < 0.001). All five patients displayed cerebellar ataxia, with peripheral neuropathy and cognitive decline or noteworthy behavioural changes. Cerebral MRI showed mild to moderate cerebellar atrophy (5/5) as well as white matter abnormalities in the cerebellum including the peridentate region (4/5), and at the periventricular level (3/5). Two-dimensional gel analyses revealed significant hyposialylation of transferrin in CSF of all patients compared to age-matched controls (P < 0.001)--a finding not present in the CSF of patients with Salla disease, the most common free sialic acid storage disorder. Free sialic acid content was normal in patients' urine and cultured fibroblasts as were plasma glycosylation patterns of transferrin. Analysis of the ganglioside profile in peripheral nerve biopsies of two out of five patients was also normal. Sequencing of four candidate genes in the free sialic acid biosynthetic pathway did not reveal any mutation. We therefore identified a new free sialic acid syndrome in which cerebellar ataxia is the leading symptom. The term CAFSA is suggested (cerebellar ataxia with free sialic acid).