title: A C9orf72 promoter repeat expansion in a Flanders-Belgian cohort with disorders of the frontotemporal lobar degeneration-amyotrophic lateral sclerosis spectrum: a gene identification study.
abstract: BACKGROUND
  Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are extremes of a clinically, pathologically, and genetically overlapping disease spectrum. A locus on chromosome 9p21 has been associated with both disorders, and we aimed to identify the causal gene within this region.
  
  
  METHODS
  We studied 305 patients with FTLD, 137 with ALS, and 23 with concomitant FTLD and ALS (FTLD-ALS) and 856 controls from Flanders (Belgium); patients were identified from a hospital-based cohort and were negative for mutations in known FTLD and ALS genes. We also examined the family of one patient with FTLD-ALS previously linked to 9p21 (family DR14). We analysed 130 kbp at 9p21 in association and segregation studies, genomic sequencing, repeat genotyping, and expression studies to identify the causal mutation. We compared genotype-phenotype correlations between mutation carriers and non-carriers.
  
  
  RESULTS
  In the patient-control cohort, the single-nucleotide polymorphism rs28140707 within the 130 kbp region of 9p21 was associated with disease (odds ratio [OR] 2·6, 95% CI 1·5-4·7; p=0·001). A GGGGCC repeat expansion in C9orf72 completely co-segregated with disease in family DR14. The association of rs28140707 with disease in the patient-control cohort was abolished when we excluded GGGGCC repeat expansion carriers. In patients with familial disease, six (86%) of seven with FTLD-ALS, seven (47%) of 15 with ALS, and 12 (16%) of 75 with FTLD had the repeat expansion. In patients without known familial disease, one (6%) of 16 with FTLD-ALS, six (5%) of 122 with ALS, and nine (4%) of 230 with FTLD had the repeat expansion. Mutation carriers primarily presented with classic ALS (10 of 11 individuals) or behavioural variant FTLD (14 of 15 individuals). Mean age at onset of FTLD was 55·3 years (SD 8·4) in 21 mutation carriers and 63·2 years (9·6) in 284 non-carriers (p=0·001); mean age at onset of ALS was 54·5 years (9·9) in 13 carriers and 60·4 years (11·4) in 124 non-carriers. Postmortem neuropathological analysis of the brains of three mutation carriers with FTLD showed a notably low TDP-43 load. In brain at postmortem, C9orf72 expression was reduced by nearly 50% in two carriers compared with nine controls (p=0·034). In familial patients, 14% of FTLD-ALS, 50% of ALS, and 62% of FTLD was not accounted for by known disease genes.
  
  
  CONCLUSIONS
  We identified a pathogenic GGGGCC repeat expansion in C9orf72 on chromosome 9p21, as recently also reported in two other studies. The GGGGCC repeat expansion is highly penetrant, explaining all of the contribution of chromosome 9p21 to FTLD and ALS in the Flanders-Belgian cohort. Decreased expression of C9orf72 in brain suggests haploinsufficiency as an underlying disease mechanism. Unidentified genes probably also contribute to the FTLD-ALS disease spectrum.
  
  
  BACKGROUND
  Full funding sources listed at end of paper (see Acknowledgments).
authors.affiliation: Department of Molecular Genetics, VIB, Antwerp, Belgium.
authors.forename: Ilse
authors.initials: I
authors.lastname: Gijselinck
authors.forename: Tim
authors.initials: T
authors.lastname: Van Langenhove
authors.forename: Julie
authors.initials: J
authors.lastname: van der Zee
authors.forename: Kristel
authors.initials: K
authors.lastname: Sleegers
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Philtjens
authors.forename: Gernot
authors.initials: G
authors.lastname: Kleinberger
authors.forename: Jonathan
authors.initials: J
authors.lastname: Janssens
authors.forename: Karolien
authors.initials: K
authors.lastname: Bettens
authors.forename: Caroline
authors.initials: C
authors.lastname: Van Cauwenberghe
authors.forename: Sandra
authors.initials: S
authors.lastname: Pereson
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Engelborghs
authors.forename: Anne
authors.initials: A
authors.lastname: Sieben
authors.forename: Peter
authors.initials: P
authors.lastname: De Jonghe
authors.forename: Rik
authors.initials: R
authors.lastname: Vandenberghe
authors.forename: Patrick
authors.initials: P
authors.lastname: Santens
authors.forename: Jan
authors.initials: J
authors.lastname: De Bleecker
authors.forename: Githa
authors.initials: G
authors.lastname: Maes
authors.forename: Veerle
authors.initials: V
authors.lastname: Bäumer
authors.forename: Lubina
authors.initials: L
authors.lastname: Dillen
authors.forename: Geert
authors.initials: G
authors.lastname: Joris
authors.forename: Ivy
authors.initials: I
authors.lastname: Cuijt
authors.forename: Ellen
authors.initials: E
authors.lastname: Corsmit
authors.forename: Ellen
authors.initials: E
authors.lastname: Elinck
authors.forename: Jasper
authors.initials: J
authors.lastname: Van Dongen
authors.forename: Steven
authors.initials: S
authors.lastname: Vermeulen
authors.forename: Marleen
authors.initials: M
authors.lastname: Van den Broeck
authors.forename: Carolien
authors.initials: C
authors.lastname: Vaerenberg
authors.forename: Maria
authors.initials: M
authors.lastname: Mattheijssens
authors.forename: Karin
authors.initials: K
authors.lastname: Peeters
authors.forename: Wim
authors.initials: W
authors.lastname: Robberecht
authors.forename: Patrick
authors.initials: P
authors.lastname: Cras
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Martin
authors.forename: Peter P
authors.initials: PP
authors.lastname: De Deyn
authors.forename: Marc
authors.initials: M
authors.lastname: Cruts
authors.forename: Christine
authors.initials: C
authors.lastname: Van Broeckhoven
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics*; D002899:Chromosomes, Human, Pair 9; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D042622:DNA Repeat Expansion; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics*; D056426:Genetic Loci; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic