Danielle Moreno

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.

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 …

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.

A novel double mutation in FUS gene causing sporadic ALS.

It has been shown that mutations in the Fused in Sarcoma gene (FUS) could explain up to 5% of cases with familial amyotrophic lateral sclerosis (ALS). Our mutation analysis of FUS in a Canadian ALS patient of Chinese origin revealed an unusual novel heterozygous double point mutation (R514S/E516V) confirming that exon 15 is a mutation hot-spot. The substitutions are in cis position to each other and affect highly conserved codons in the RGG-rich region of the FUS protein. The absence of clinical signs of ALS in the relatives of the affected carrier could indicate that this mutation is incompletely penetrant or de novo. The pathologic significance of the R514S/E516V mutation was confirmed by immunohistochemistry. FUS-positive cytoplasmic inclusions were noted in a moderate number in neurons and abundantly in glial cells in the motor cortex and the brainstem. Of interest, a significant number of neuronal and glial FUS-positive inclusions were found in the tegmentum of the brainstem. Importantly, some neurons with inclusions showed retention of the normal nuclear FUS immunostaining.

A mechanism for low penetrance in an ALS family with a novel SOD1 deletion.

Background: About 20% of familial amyotrophic lateral sclerosis (ALS) is caused by mutations in SOD1 and is typically transmitted as an autosomal dominant trait. However, due to reduced mutation penetrance, the disease may present in a recessive or sporadic manner. Objective: To determine the factors responsible for the low penetrance of the SOD1 mutation. Methods: Twelve members of a Canadian ALS family of Filipino origin were recruited for the study. SOD1 was sequenced in the proband. SOD1 expression was assessed by real-time-PCR and immunoblotting. Results: The proband was a homozygous carrier of a novel 6 bp deletion in exon 2 (ΔG27/P28), the pathologic significance of which was confirmed by immunohistochemistry. Eight living family members are heterozygotes and remain unaffected at ages ranging between 48 and 85 years. Haplotype analysis showed that the deletion is a single founder mutation likely common in the Cagayan province (Philippines). The low penetrance of the mutation is explained by the fact that it enhances the naturally occurring alternative splicing of exon 2 of the SOD1 mRNA, leading to reduced transcription of the mutant allele. Indeed, Western blot analysis demonstrated the low level of SOD1 protein in carriers of the ΔG27/P28 compared to wild-type individuals or a carrier of the A4V SOD1 mutation. Conclusion: The enhanced splicing of exon 2 acts as a natural knock-down of the mutant SOD1 allele in the Filipino amyotrophic lateral sclerosis (ALS) family. There is a need for careful investigation of splicing isoforms of SOD1 and other ALS genes as factors influencing the severity of disease.

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

The G2019S LRRK2 Mutation in Brazilian Patients with Parkinson's Disease : Phenotype in Monozygotic Twins

Mutations in the Leucine‐Rich Repeat Kinase 2 gene (LRRK2) are mainly responsible for idiopathic Parkinsons disease (PD) with either a dominant pattern of transmission or a sporadic occurrence due to the reduced penetrance. A majority of LRRK2 kindreds demonstrate an extremely variable age‐at‐onset in affected members of the same family. The G2019S is the most common LRRK2 mutation, which accounts for 1–5% PD patients in North America, and up to 40% of patients from an isolated Arab population. We assessed the frequency of the G2019S mutation in 83 Brazilian PD patients originally preselected for having an early age‐at‐onset (<50 years) and/or a positive family history. The mutation was detected in three probands (3.5%). Our clinical findings in these kindreds include the first description of the phenotype in identical twins discordant for handedness (a general phenomenon found in ∼25% monozygotic twins). However, both twins developed right asymmetric PD. The clinical presentation of twins was strikingly similar including an identical PD onset at age 60. This observation may suggest that genetic factors predominantly determine age‐at‐onset.

Mutation analysis of patients with neurodegenerative disorders using NeuroX array

Genetic analyses of patients with neurodegenerative disorders have identified multiple genes that need to be investigated for the presence of damaging variants. However, mutation analysis by Sanger sequencing is costly and time consuming. We tested the utility of a recently designed semi-custom genome-wide array (NeuroX; Illumina, Inc) tailored to study neurodegenerative diseases (e.g., mutation screening). We investigated 192 patients with 4 different neurodegenerative disorders for the presence of rare damaging variations in 77 genes implicated in these diseases. Several causative mutations were identified and confirmed by Sanger sequencing, including PSEN1 p.M233T responsible for Alzheimers disease in a large Italian family, as well as SOD1 p.A4V and p.I113T in patients with amyotrophic lateral sclerosis. In total, we identified 78 potentially damaging rare variants (frequency <1%), including ABCA7 p.L400V in a family with Alzheimers disease and LRRK2 p.R1514Q in 6 of 98 patients with Parkinsons disease (6.1%). In conclusion, NeuroX appears to be helpful for rapid and accurate mutation screening, although further development may be still required to improve some current caveats.

Mutation analysis of CHCHD2 in Canadian patients with familial Parkinson's disease

Recently, several CHCHD2 mutations were reported to be associated with autosomal dominant Parkinsons disease (PD) in a Japanese population. However, an association between CHCHD2 and PD was not observed in 2 Caucasian data sets. The present study searched for CHCHD2 coding variants in Canadian PD patients. Sanger sequencing of all CHCHD2 exons revealed no coding mutations in 155 familial cases. Moreover, 3 coding CHCHD2 polymorphisms available on the NeuroX array (Pro2Leu, Pro14Ser, and Ile118Met) were homozygous for the major allele in an additional 85 PD patients. Our study suggests that CHCHD2 mutations may not account for PD in Canadian patients.