title: A novel splice-site mutation in ALS2 establishes the diagnosis of juvenile amyotrophic lateral sclerosis in a family with early onset anarthria and generalized dystonias.
abstract: The diagnosis of childhood neurological disorders remains challenging given the overlapping clinical presentation across subgroups and heterogeneous presentation within subgroups. To determine the underlying genetic cause of a severe neurological disorder in a large consanguineous Pakistani family presenting with severe scoliosis, anarthria and progressive neuromuscular degeneration, we performed genome-wide homozygosity mapping accompanied by whole-exome sequencing in two affected first cousins and their unaffected parents to find the causative mutation. We identified a novel homozygous splice-site mutation (c.3512+1G>A) in the ALS2 gene (NM_020919.3) encoding alsin that segregated with the disease in this family. Homozygous loss-of-function mutations in ALS2 are known to cause juvenile-onset amyotrophic lateral sclerosis (ALS), one of the many neurological conditions having overlapping symptoms with many neurological phenotypes. RT-PCR validation revealed that the mutation resulted in exon-skipping as well as the use of an alternative donor splice, both of which are predicted to cause loss-of-function of the resulting proteins. By examining 216 known neurological disease genes in our exome sequencing data, we also identified 9 other rare nonsynonymous mutations in these genes, some of which lie in highly conserved regions. Sequencing of a single proband might have led to mis-identification of some of these as the causative variant. Our findings established a firm diagnosis of juvenile ALS in this family, thus demonstrating the use of whole exome sequencing combined with linkage analysis in families as a powerful tool for establishing a quick and precise genetic diagnosis of complex neurological phenotypes.
authors.affiliation: Institute of Biomedical and Genetic Engineering (IBGE), Islamabad, Pakistan.
authors.forename: Saima
authors.initials: S
authors.lastname: Siddiqi
authors.affiliation: Human Genetics, Genome Institute of Singapore, A*STAR, Singapore, Singapore.
authors.forename: Jia Nee
authors.initials: JN
authors.lastname: Foo
authors.affiliation: Department of Cellular and Molecular Medicine and Institute for Genomic Medicine, University of California at San Diego, La Jolla, California, United States of America.
authors.forename: Anthony
authors.initials: A
authors.lastname: Vu
authors.affiliation: Ali Medical Center, F8/1, Islamabad, Pakistan.
authors.forename: Saad
authors.initials: S
authors.lastname: Azim
authors.affiliation: Signature Research Program in Cardiovascular & Metabolic Disorders, Duke-NUS Graduate Medical School, Singapore, Singapore.
authors.forename: David L
authors.initials: DL
authors.lastname: Silver
authors.affiliation: Institute of Biomedical and Genetic Engineering (IBGE), Islamabad, Pakistan.
authors.forename: Atika
authors.initials: A
authors.lastname: Mansoor
authors.affiliation: Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Stacey Kiat Hong
authors.initials: SK
authors.lastname: Tay
authors.affiliation: International Islamic University, Islamabad, Pakistan.
authors.forename: Sumiya
authors.initials: S
authors.lastname: Abbasi
authors.affiliation: Institute of Biomedical and Genetic Engineering (IBGE), Islamabad, Pakistan.
authors.forename: Asraf Hussain
authors.initials: AH
authors.lastname: Hashmi
authors.affiliation: College of Physicians and Surgeons (CPSP), Islamabad, Pakistan.
authors.forename: Jamal
authors.initials: J
authors.lastname: Janjua
authors.affiliation: International Islamic University, Islamabad, Pakistan.
authors.forename: Sumbal
authors.initials: S
authors.lastname: Khalid
authors.affiliation: Signature Research Program in Cardiovascular & Metabolic Disorders, Duke-NUS Graduate Medical School, Singapore, Singapore; Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, National University Hospital System, Singapore, Singapore; Saw Swee Hock School of Public Health, National University of Singapore, National University Hospital System, Singapore, Singapore.
authors.forename: E Shyong
authors.initials: ES
authors.lastname: Tai
authors.affiliation: Department of Cellular and Molecular Medicine and Institute for Genomic Medicine, University of California at San Diego, La Jolla, California, United States of America; Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Gene W
authors.initials: GW
authors.lastname: Yeo
authors.affiliation: Human Genetics, Genome Institute of Singapore, A*STAR, Singapore, Singapore; Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Chiea Chuen
authors.initials: CC
authors.lastname: Khor
mesh_terms: D000293:Adolescent; D000328:Adult; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000503:physiopathology; D044466:Asian People; D002648:Child; D002675:Child, Preschool; D020821:Dystonic Disorders / Q000235:genetics / Q000503:physiopathology; D005091:Exons; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics*; D006801:Humans; D007223:Infant; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D010641:Phenotype; D022821:RNA Splice Sites / Q000235:genetics*
chemical_list: C438187:ALS2 protein, human; D020662:Guanine Nucleotide Exchange Factors; D022821:RNA Splice Sites