TMEM106B is a Genetic Modifier of Frontotemporal Lobar Degeneration with C9orf72 Hexanucleotide Repeat Expansions (I5-1.008)
Alice Chen‐PlotkinMichael GallagherEunRan SuhMurray GrossmanLauren ElmanLeo McCluskeyJohn Q. TrojanowskiVirginia M.‐Y. LeeVivianna M. Van Deerlin
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C9ORF72
Frontotemporal lobar degeneration
Degeneration (medical)
Abstract The PET ligand [ 18 F] AV ‐1451 was developed to bind tau pathology in Alzheimer's disease, but increased binding has been shown in both genetic tauopathies and in semantic dementia, a disease strongly associated with TDP ‐43 pathology. Here we assessed [ 18 F] AV ‐1451 binding in behavioral variant frontotemporal dementia due to a hexanucleotide repeat expansion in C9orf72, characterized by TDP ‐43 pathology. We show that the C9orf72 mutation increases binding in frontotemporal cortex, with a distinctive distribution of binding compared with healthy controls.
C9ORF72
Frontotemporal lobar degeneration
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Semantic dementia
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C9ORF72
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TDP-43 is the main protein component of ubiquitinated inclusions in a subgroup of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) patients. The C9ORF72 hexanucleotide expansion is one of the main mutations associated with TDP-43 pathology in FTLD and ALS. Our aim was to analyze cerebrospinal fluid (CSF) TDP-43 levels and Alzheimer's disease biomarkers in FTLD and ALS patients and to test whether the C9ORF72 expansion carrier status affects these variables.The patient cohort consisted of 90 clinically well-characterized FTLD (n = 69) and ALS (n = 21) patients. There were 30 patients with the C9ORF72 expansion and 60 patients without the expansion. CSF TDP-43, AΒ1-42, t-tau, and phospho-tau levels were measured using commercial ELISA kits.There was no difference in CSF TDP-43 levels between the C9ORF72 expansion carriers and the noncarriers. CSF TDP-43 levels were higher in ALS patients than in FTLD patients, and this finding was independent of the C9ORF72 expansion carrier status. Males had significantly higher TDP-43 levels than females (p = 0.008 in the total cohort).CSF TDP-43 does not seem to distinguish the C9ORF72 expansion carriers from noncarriers. However, higher CSF TDP-43 levels were detected in ALS than in FTLD, which might be an indicator of a more rapid progression of TDP-43 pathology in ALS.
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Motor neurone disease
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Frontotemporal dementia (FTD) is an uncommon but important form of degenerative disease characterized by clinical syndromes that result from degeneration of the frontal and temporal lobes. FTD is divided based on clinical presentation into behavioral variant FTD (bvFTD), semantic dementia, and progressive nonfluent/agrammatic aphasia. Several recent studies have advanced our knowledge of the genetics of FTD, with the three most common FTD genes being microtubule-associated protein tau (MAPT) and progranulin (GRN), and a noncoding repeat expansion in C9ORF72. Tau and TDP-43 are the most common pathologies associated with FTD. No pharmacological therapies are currently approved for use in FTD.
C9ORF72
Frontotemporal lobar degeneration
Semantic dementia
Primary progressive aphasia
Tauopathy
Corticobasal degeneration
Tau protein
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Hexanucleotide repeat expansions within the C9orf72 gene are the most important genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The difficulty of developing a precise method to determine the expansion size has hampered the study of possible correlations between the hexanucleotide repeat number and clinical phenotype. Here we characterize, through a new non-radioactive Southern blot protocol, the expansion size range in a series of 38 ALS and 22 FTD heterozygous carriers of >30 copies of the repeat. Maximum, median and modal hexanucleotide repeat number were higher in ALS patients than in FTD patients (P< 0.05 in all comparisons). A higher median number of repeats correlated with a bigger range of repeat sizes (Spearman's ρ = 0.743, P = 1.05 × 10–11). We did not find any correlation between age of onset or disease duration with the repeat size in neither ALS nor FTD mutation carriers. Clinical presentation (bulbar or spinal) in ALS patients did not correlate either with the repeat length. We finally analyzed two families with affected and unaffected repeat expansion carriers, compared the size of the repeat expansion between two monozygotic (MZ) twins (one affected of ALS and the other unaffected), and examined the expansion size in two different tissues (cerebellum and peripheral blood) belonging to the same FTD patient. The results suggested that the length of the C9orf72 repeat varies between family members, including MZ twins, and among different tissues from the same individual.
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Amyotrophic lateral sclerosis and frontotemporal dementia are significant neurodegenerative illnesses with possible genetic predispositions. The C9orf72 gene and the GGGGCC repeat expansions of it are reported to have a causative role in the expression of these conditions. We report a case of a patient with autosomal dominant amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD) in the presence of C9orf72 repeat expansion. We believe our case further supports the theory that the presence of C9orf72 repeat expansion in patients with a family history of amyotrophic lateral sclerosis and/or frontotemporal dementia significantly increases their risk of developing either or both diseases. The development of antisense oligonucleotides that might target GGGGCC RNA sequences theoretically may have a therapeutic role in mitigating the clinical expression of these illnesses.
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