Mahdi Ghani

Investigation of C9orf72 in 4 Neurodegenerative Disorders

OBJECTIVE To estimate the allele frequency of C9orf72 (G4C2) repeats in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Alzheimer disease (AD), and Parkinson disease (PD). DESIGN The number of repeats was estimated by a 2-step genotyping strategy. For expansion carriers, we sequenced the repeat flanking regions and obtained APOE genotypes and MAPT H1/H2 haplotypes. SETTING Hospitals specializing in neurodegenerative disorders. SUBJECTS We analyzed 520 patients with FTLD, 389 patients with ALS, 424 patients with AD, 289 patients with PD, 602 controls, 18 families, and 29 patients with PD with the LRRK2 G2019S mutation. MAIN OUTCOME MEASURE The expansion frequency. RESULTS Based on a prior cutoff (>30 repeats), the expansion was detected in 9.3% of patients with ALS, 5.2% of patients with FTLD, and 0.7% of patients with PD but not in controls or patients with AD. It was significantly associated with family history of ALS or FTLD and age at onset of FTLD. Phenotype variation (ALS vs FTLD) was not associated with MAPT, APOE, or variability in the repeat flanking regions. Two patients with PD were carriers of 39 and 32 repeats with questionable pathological significance, since the 39-repeat allele does not segregate with PD. No expansion or intermediate alleles (20-29 repeats) were found among the G2019S carriers and AD cases with TAR DNA-binding protein 43-positive inclusions. Surprisingly, the frequency of the 10-repeat allele was marginally increased in all 4 neurodegenerative diseases compared with controls, indicating the presence of an unknown risk variation in the C9orf72 locus. CONCLUSIONS The C9orf72 expansion is a common cause of ALS and FTLD, but not of AD or PD. Our study raises concern about a reliable cutoff for the pathological repeat number, which is important in the utility of genetic screening.

Rare coding mutations identified by sequencing of Alzheimer disease genome-wide association studies loci

To detect rare coding variants underlying loci detected by genome‐wide association studies (GWAS) of late onset Alzheimer disease (LOAD).

Coding mutations in SORL1 and Alzheimer disease.

Common single nucleotide polymorphisms in the SORL1 gene have been associated with late onset Alzheimer disease (LOAD), but causal variants have not been fully characterized nor has the mechanism been established. The study was undertaken to identify functional SORL1 mutations in patients with LOAD.

Rare coding mutations identified by sequencing of Alzheimer's disease GWAS loci

To detect rare coding variants underlying loci detected by genome‐wide association studies (GWAS) of late onset Alzheimer disease (LOAD).

Genetic association of CR1 with Alzheimer's disease: A tentative disease mechanism

CR1 is a novel Alzheimers disease (AD) gene identified by genome-wide association studies (GWAS). Recently, we showed that AD risk could be explained by an 18-kilobase insertion responsible for the complement component (3b/4b) receptor 1 (CR1)-S isoform. We investigated the relevance of the CR1 isoforms to AD in a Canadian dataset. Also, we genotyped rs4844610 tagging the GWAS-significant CR1 single nucleotide polymorphisms. Individuals with F/S genotype had a 1.8 times increased risk for AD compared with F/F genotype (p-adjusted = 0.003), while rs4844610 was only marginally significant (p-adjusted = 0.024). The analyses of brain samples demonstrated that the CR1-S isoform is expressed at lower protein levels than CR1-F (p < 0.0001) hence likely associated with increased complement activation. Intriguingly, our neuropathological results show that the pattern of CR1 expression in neurons is different between the F/F and F/S genotypes (filiform vs. vesicular-like profiles). Furthermore, double labeling studies supported a differential distribution of CR1 in neurons (endoplasmic reticulum intermediate compartment vs. lysosomes). These observations indicate that the CR1-S and CR1-F isoforms could be processed in different ways in neurons. In conclusion, our results support that the CR1-S isoform explains the GWAS signals and open a novel prospect for the investigation of CR1-related disease mechanisms.

Mutation analysis of CHCHD10 in different neurodegenerative diseases

Sir, A recent study by Bannwarth et al. (2014) implicated CHCHD10 as a novel gene for amyotrophic lateral sclerosis/frontotemporal lobar degeneration (ALS/FTLD), reporting a p.S59L substitution (c.176C > T; NM_213720.2) in a large French kindred. Affected family members were presented with a complex phenotype that included symptoms of amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), cerebellar ataxia, Parkinson’s disease and a mitochondrial myopathy associated with multiple mitochondrial DNA deletions. So far, seven missense CHCHD10 mutations have been reported in patients with a broad phenotypic range, including ALS/FTLD (p.S59L and p.P34S) (Bannwarth et al. , 2014; Chaussenot et al. , 2014), ALS (p.R15L and p.G66V) (Johnson et al. , 2014; Muller et al. , 2014), myopathy (p.R15S and p.G58R) (Ajroud-Driss et al. , 2015) and late-onset spinal motor neuronopathy (p.G66V) (Penttila et al. , 2015). All of them affect exon 2 (a mutational hotspot of CHCHD10 ). Notably, mitochondrial dysfunction has been implicated in several neurodegenerative diseases (Lin and Beal, 2006; Cozzolino et al. , 2013); however, there are no studies evaluating the contribution of CHCHD10 to pure FTLD, Parkinson’s disease or Alzheimer’s disease. Hence, we sequenced CHCHD10 exon 2 in 204 ALS, 153 Parkinson’s disease and 141 Alzheimer’s disease patients from Canada and 158 FTLD patients from Italy in addition to 497 control subjects from USA/UK, Canada and Italy. The cases of ALS and FTLD were free from mutations in SOD1 , GRN , FUS , TARDBP and MATR3 or a repeat expansion in C9orf72 . We identified a known CHCHD10 pathogenic p.R15L mutation (Johnson et al. , 2014; Muller et al. , 2014) in a patient with sporadic ALS (Patient 8807) (Fig. 1A), who developed symptoms involving his upper limb at 54 years of age and remains alive 12 years later. The p.R15L …

Independent and epistatic effects of variants in VPS10-d receptors on Alzheimer disease risk and processing of the amyloid precursor protein (APP)

Genetic variants in the sortilin-related receptor (SORL1) and the sortilin-related vacuolar protein sorting 10 (VPS10) domain-containing receptor 1 (SORCS1) are associated with increased risk of Alzheimer’s disease (AD), declining cognitive function and altered amyloid precursor protein (APP) processing. We explored whether other members of the (VPS10) domain-containing receptor protein family (the sortilin-related VPS10 domain-containing receptors 2 and 3 (SORCS2 and SORCS3) and sortilin (SORT1)) would have similar effects either independently or together. We conducted the analyses in a large Caucasian case control data set (n=11 840 cases, 10 931 controls) to determine the associations between single nucleotide polymorphisms (SNPs) in all the five homologous genes and AD risk. Evidence for interactions between SNPs in the five VPS10 domain receptor family genes was determined in epistatic statistical models. We also compared expression levels of SORCS2, SORCS3 and SORT1 in AD and control brains using microarray gene expression analyses and assessed the effects of these genes on γ-secretase processing of APP. Several SNPs in SORL1, SORCS1, SORCS2 and SORCS3 were associated with AD. In addition, four specific linkage disequilibrium blocks in SORCS1, SORCS2 and SORCS3 showed additive epistatic effects on the risk of AD (P⩽0.0006). SORCS3, but not SORCS2 or SORT1, showed reduced expression in AD compared with control brains, but knockdown of all the three genes using short hairpin RNAs in HEK293 cells caused a significant threefold increase in APP processing (from P<0.001 to P<0.05). These findings indicate that in addition to SORL1 and SORCS1, variants in other members of the VPS10 domain receptor family (that is, SORCS1, SORCS2, SORCS3) are associated with AD risk and alter APP processing. More importantly, the results indicate that variants within these genes have epistatic effects on AD risk.

Evidence of Recessive Alzheimer Disease Loci in a Caribbean Hispanic Data Set: Genome-wide Survey of Runs of Homozygosity

IMPORTANCE The search for novel Alzheimer disease (AD) genes or pathologic mutations within known AD loci is ongoing. The development of array technologies has helped to identify rare recessive mutations among long runs of homozygosity (ROHs), in which both parental alleles are identical. Caribbean Hispanics are known to have an elevated risk for AD and tend to have large families with evidence of inbreeding. OBJECTIVE To test the hypothesis that the late-onset AD in a Caribbean Hispanic population might be explained in part by the homozygosity of unknown loci that could harbor recessive AD risk haplotypes or pathologic mutations. DESIGN We used genome-wide array data to identify ROHs (>1 megabase) and conducted global burden and locus-specific ROH analyses. SETTING A whole-genome case-control ROH study. PARTICIPANTS A Caribbean Hispanic data set of 547 unrelated cases (48.8% with familial AD) and 542 controls collected from a population known to have a 3-fold higher risk of AD vs non-Hispanics in the same community. Based on a Structure program analysis, our data set consisted of African Hispanic (207 cases and 192 controls) and European Hispanic (329 cases and 326 controls) participants. EXPOSURE Alzheimer disease risk genes. MAIN OUTCOMES AND MEASURES We calculated the total and mean lengths of the ROHs per sample. Global burden measurements among autosomal chromosomes were investigated in cases vs controls. Pools of overlapping ROH segments (consensus regions) were identified, and the case to control ratio was calculated for each consensus region. We formulated the tested hypothesis before data collection. RESULTS In total, we identified 17 137 autosomal regions with ROHs. The mean length of the ROH per person was significantly greater in cases vs controls (P = .0039), and this association was stronger with familial AD (P = .0005). Among the European Hispanics, a consensus region at the EXOC4 locus was significantly associated with AD even after correction for multiple testing (empirical P value 1 [EMP1], .0001; EMP2, .002; 21 AD cases vs 2 controls). Among the African Hispanic subset, the most significant but nominal association was observed for CTNNA3, a well-known AD gene candidate (EMP1, .002; 10 AD cases vs 0 controls). CONCLUSIONS AND RELEVANCE Our results show that ROHs could significantly contribute to the etiology of AD. Future studies would require the analysis of larger, relatively inbred data sets that might reveal novel recessive AD genes. The next step is to conduct sequencing of top significant loci in a subset of samples with overlapping ROHs.

Epidemiology and genetics of frontotemporal dementia: a door-to-door survey in Southern Italy

The objectives of this study were to estimate frontotemporal dementia (FTD) prevalence, identify FTD-related mutations, and correlate FTD phenotype with mutations in a southern Italian population. The study population consisted of subjects ≥ 50 years of age residing in the Community of Biv. on January 1, 2004, and a door-to-door 2-phase design was used. Genetic and biochemical analyses were done on samples collected from 32 patients. Prevalence rates were 0.6 for Alzheimers disease, 0.4 for vascular dementia (VD), 3.5 for FTD, 0.2 for Parkinson dementia, and 1.2 for unspecified dementia. Three GRN (1 known and 2 novel) mutations with reduced plasma protein levels were found associated to 3 distinct phenotypes (behavioral, affective, and delirious type). We report an unusually high FTD prevalence in the investigated population, but a low prevalence of Alzheimers disease. We confirm the heterogeneity of FTD phenotype associated with different GRN mutations.

Identical twins with the C9orf72 repeat expansion are discordant for ALS

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease that could co-occur with frontotemporal dementia (FTD), characterized by early behavioral or language changes. Mutations causing ALS and FTD have been found in several often overlapping genes.1 The most common mutation for both syndromes is a noncoding G4C2 expansion in C9orf72,2,3 usually ranging from hundreds to thousands of repeats.4 Currently it is unclear whether expansion alleles with different sizes have the same pathologic consequence, and the lower limit for pathologic repeat number has not been determined.4,5