J Alzheimers Dis. 2012 Dec 19. [Epub ahead of print]
C9ORF72 Repeat Expansions in the Frontotemporal Dementias Spectrum of Diseases: A Flowchart for Genetic Testing.
Le Ber I, Camuzat A, Guillot-Noel L, Hannequin D, Lacomblez L, Golfier V, Puel M, Martinaud O, Deramecourt V, Rivaud-Pechoux S, Millecamps S, Vercelletto M, Couratier P, Sellal F, Pasquier F, Salachas F, Thomas-Antérion C, Didic M, Pariente J, Seilhean D, Ruberg M, Wargon I, Blanc F, Camu W, Michel BF, Berger E, Sauvée M, Thauvin-Robinet C, Mondon K, Tournier-Lasserve E, Goizet C, Fleury M, Viennet G, Verpillat P, Meininger V, Duyckaerts C, Dubois B, Brice A.
SourceCRicm-UMRS975, Paris, France AP-HP, Hôpital de la Pitié-Salpêtrière, Centre de Référence des Démences Rares, Paris, France AP-HP, Hôpital de la Pitié-Salpêtrière, Fédération des maladies du système nerveux, Paris, France.
AbstractFrontotemporal dementia (FTD) refers to a disease spectrum including the behavioral variant FTD (bvFTD), primary progressive aphasia (PPA), progressive supranuclear palsy/corticobasal degeneration syndrome (PSP/CBDS), and FTD with amyotrophic lateral sclerosis (FTD-ALS). A GGGGCC expansion in C9ORF72 is a major cause of FTD and ALS. C9ORF72 was analyzed in 833 bvFTD, FTD-ALS, PPA, and PSP/CBDS probands; 202 patients from 151 families carried an expansion. C9ORF72 expansions were much more frequent in the large subgroup of patients with familial FTD-ALS (65.9%) than in those with pure FTD (12.8%); they were even more frequent than in familial pure ALS, according to estimated frequencies in the literature (23-50%). The frequency of carriers in non-familial FTD-ALS (12.7%) indicates that C9ORF72 should be analyzed even when family history is negative. Mutations were detected in 6.8% of PPA patients, and in 3.2% of patients with a clinical phenotype of PSP, thus enlarging the phenotype spectrum of C9ORF72. Onset was later in C9ORF72 (57.4 years, 95%CI: 55.9-56.1) than in MAPT patients (46.8, 95%CI: 43.0-50.6; p = 0.00001) and the same as in PGRN patients (59.6 years; 95%CI: 57.6-61.7; p = 0.4). ALS was more frequent in C9ORF72 than in MAPT and PGRN patients; onset before age 50 and parkinsonism were indicative of MAPT mutations, whereas hallucinations were indicative of PGRN mutations; prioritization of genetic testing is thus possible. Penetrance was age- and gender-dependent: by age 50, 78% of male carriers were symptomatic, but only 52% of females. This can also guide genetic testing and counseling. A flowchart for genetic testing is thus proposed.
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