title: Whole-genome sequencing reveals a coding non-pathogenic variant tagging a non-coding pathogenic hexanucleotide repeat expansion in C9orf72 as cause of amyotrophic lateral sclerosis.
abstract: Motor neuron degeneration in amyotrophic lateral sclerosis (ALS) has a familial cause in 10% of patients. Despite significant advances in the genetics of the disease, many families remain unexplained. We performed whole-genome sequencing in five family members from a pedigree with autosomal-dominant classical ALS. A family-based elimination approach was used to identify novel coding variants segregating with the disease. This list of variants was effectively shortened by genotyping these variants in 2 additional unaffected family members and 1500 unrelated population-specific controls. A novel rare coding variant in SPAG8 on chromosome 9p13.3 segregated with the disease and was not observed in controls. Mutations in SPAG8 were not encountered in 34 other unexplained ALS pedigrees, including 1 with linkage to chromosome 9p13.2-23.3. The shared haplotype containing the SPAG8 variant in this small pedigree was 22.7 Mb and overlapped with the core 9p21 linkage locus for ALS and frontotemporal dementia. Based on differences in coverage depth of known variable tandem repeat regions between affected and non-affected family members, the shared haplotype was found to contain an expanded hexanucleotide (GGGGCC)(n) repeat in C9orf72 in the affected members. Our results demonstrate that rare coding variants identified by whole-genome sequencing can tag a shared haplotype containing a non-coding pathogenic mutation and that changes in coverage depth can be used to reveal tandem repeat expansions. It also confirms (GGGGCC)n repeat expansions in C9orf72 as a cause of familial ALS.
authors.affiliation: Department of Neurology, University of Leuven, Leuven, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Herdewyn
authors.forename: Hui
authors.initials: H
authors.lastname: Zhao
authors.forename: Matthieu
authors.initials: M
authors.lastname: Moisse
authors.forename: Valérie
authors.initials: V
authors.lastname: Race
authors.forename: Gert
authors.initials: G
authors.lastname: Matthijs
authors.forename: Joke
authors.initials: J
authors.lastname: Reumers
authors.forename: Benno
authors.initials: B
authors.lastname: Kusters
authors.forename: Helenius J
authors.initials: HJ
authors.lastname: Schelhaas
authors.forename: Leonard H
authors.initials: LH
authors.lastname: van den Berg
authors.forename: An
authors.initials: A
authors.lastname: Goris
authors.forename: Wim
authors.initials: W
authors.lastname: Robberecht
authors.forename: Diether
authors.initials: D
authors.lastname: Lambrechts
authors.forename: Philip
authors.initials: P
authors.lastname: Van Damme
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000473:pathology; D000073885:C9orf72 Protein; D002874:Chromosome Mapping; D042622:DNA Repeat Expansion; D005260:Female; D014644:Genetic Variation; D015894:Genome, Human; D006239:Haplotypes; D006801:Humans; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins