High repeat expansion (HRE) alleles in
have been linked to both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD); ranges for intermediate allelic expansions have not been defined ...yet, and clinical interpretation of molecular data lacks a defined genotype-phenotype association. In this study, we provide results from a large multicenter epidemiological study reporting the distribution of
repeats in healthy elderly from the Italian population.
A total of 967 samples were collected from neurologically evaluated healthy individuals over 70 years of age in the 13 institutes participating in the RIN (IRCCS Network of Neuroscience and Neurorehabilitation) based in Italy. All samples were genotyped using the AmplideXPCR/CE
Kit (Asuragen, Inc.), using standardized protocols that have been validated through blind proficiency testing.
All samples carried hexanucleotide G
C
expansion alleles in the normal range. All samples were characterized by alleles with less than 25 repeats. In particular, 93.7% of samples showed a number of repeats ≤10, 99.9% ≤20 repeats, and 100% ≤25 repeats.
This study describes the distribution of hexanucleotide G
C
expansion alleles in an Italian healthy population, providing a definition of alleles associated with the neurological healthy phenotype. Moreover, this study provides an effective model of federation between institutes, highlighting the importance of sharing genomic data and standardizing analysis techniques, promoting translational research. Data derived from the study may improve genetic counseling and future studies on ALS/FTD.
Abstract Abnormal expansion of a hexanucleotide GGGGCC (G4 C2 ) repeat in the C9orf72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in ...Caucasians. However, the underlying pathological mechanisms remain controversial, and both loss-of-function and gain-of-function models have been proposed. To gain further insight into these mechanisms, we performed mutation analysis of C9orf72 in 276 Han Chinese patients with ALS. We identified G4C2 expansions in two cases of sporadic ALS (SALS) with 38 and 63 repeats, as well as a novel splice site mutation (c.601-2A>G) in a third case. These genetic alterations were not detected in 332 control patients without neurological disease. Intriguingly, functional analysis revealed that the splice site mutation disrupted the reading frame, creating a premature stop codon (p.I201fsX235). Decreased levels of the mutant mRNA were detected in patient cells, suggesting that it may undergo nonsense-mediated mRNA decay. Taken together, these results demonstrate that C9orf72 mutation is infrequently associated with ALS in Han Chinese patients and suggest that a splice site mutation in C9orf72 may lead to loss of function due to haploinsufficiency of the resulting protein.
Objective: Expansion of the G
4
C
2
repeat tract in the C9orf72 gene is linked to frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Here, we provide comprehensive genotyping of ...the C9orf72 repeat region for the National Institute of Neurological Disorders and Stroke (NINDS) ALS collection (n = 2095), using a novel bimodal PCR assay capable of amplifying nearly 100% GC-rich sequences. Methods: A single-tube 3-primer PCR assay mode, resolved using capillary electrophoresis, was used for sizing up to 145 repeats with single-repeat accuracy, for detecting expansions irrespective of their overall size, and for flagging confounding 3′ sequence variations (SVs). A modified two-primer PCR mode, resolved via agarose gel electrophoresis, provided further size information for hyper-expanded samples (>145 repeats) up to ∼5.8 kb amplicons (∼950 G
4
C
2
repeats). Results: Within the evaluated cohort, 177 (8.4%) samples were expanded, with 175 (99%) samples being hyper-expanded. 3′-SVs were identified in 64 (3.1%) samples, and were most common in expanded alleles. Genotypes of all 606 (29%) homozygous samples were confirmed using an orthogonal PCR assay. Conclusion: This study and PCR method may improve and standardize molecular characterization of the C9orf72 locus, and have the potential to inform phenotype-genotype correlations and therapeutic development in ALS/FTD.
Abstract Parkinsonism might precede, coincide, or follow the behavioral or language-predominant cognitive impairments characteristic of frontotemporal dementia (FTD). In this study, we analyze the ...hexanucleotide repeat expansions within C9orf72 gene in various parkinsonian syndromes because it is a recently identified important genetic cause of FTD. The expanded hexanucleotide repeat is only identified in our familial FTD patients but not in patients with predominant parkinsonism. The lack of association between abnormal C9orf72 repeat expansion and parkinsonian syndromes might imply pathogenic mechanisms other than tau or Lewy body pathology.
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