, 2011 and Vance et al., 2006). Using a genome-wide association study (GWAS) approach, we recently reported that this locus on chromosome 9p21 accounted for nearly half of familial ALS and nearly one-quarter of all ALS cases in a cohort of 405 Finnish patients and 497 control samples (Laaksovirta et al., 2010). This association signal had previously been reported by van Es and colleagues (van Es et al., 2009), and a meta-analysis involving 4,312 cases and 8,425 controls confirmed that chromosome 9p21 was the major signal for ALS (Shatunov et al., 2010). A recent GWAS for FTD also identified this locus (Van Deerlin et al., 2010). Analysis

in the Finnish population narrowed the association to a 232 kilobase (kb) block of linkage disequilibrium and allowed the identification of a founder haplotype that increased risk of disease by over 20-fold. The selleck associated haplotype appears to be the same in all European-ancestry populations, and several families previously shown to have genetic linkage to the chromosome 9p21 region also share this risk haplotype (Mok et al., 2011). We have previously identified an ALS-FTD family from the UK and an apparently unrelated ALS-FTD family from the Netherlands that showed positive linkage to the chromosome 9p21 Antidiabetic Compound Library concentration region (Mok et al., 2011 and Pearson et al., 2011). Using these families and the Finnish ALS cases that

had previously been used to identify the chromosome 9p21 association signal, we undertook a methodical assessment of the region using next-generation only sequencing technology in an attempt

to identify the genetic lesion responsible for disease. We undertook massively parallel, next-generation, deep resequencing of the chromosome 9p21 region in (1) DNA that had been flow-sorted enriched for chromosome 9 obtained from an affected member of the GWENT#1 kindred (IV-3, Figure 1A; Coriell ID ND06769) and from a neurologically normal control (ND11463); and (2) DNA that had been enriched for the target region using custom oligonucleotide baits obtained from three cases and five unaffected members of the DUTCH#1 kindred (V-1, V-3, and V-14, and V-2, V4, V5, VI-1, and spouse of V-1; Figure 1B). Analysis of the GWENT#1 sequence data revealed eight novel variants within the 232 kb block of linkage disequilibrium containing the previously identified association signal that were not described as polymorphisms in either the 1000 Genomes (April 2009 release) or the dbSNP (build 132) online databases. Six of these variants were located within a 30 base pair (bp) region. When the individual sequence reads within this region were examined and manually realigned, they indicated the presence of a hexanucleotide repeat expansion GGGGCC located 63 bp centromeric to the first exon of the long transcript of C9ORF72 (RefSeq accession number = NM_018325.2; GenBank accession number = GI:209863035) in the affected cases that was not present in the control samples (see Figure S1 available online for individual reads).