Brief communication Screening for rare variants in the coding region of ALS-associated genes at 9p21.2 and 19p13.3 Max Koppers a, b,1 , Ewout J.N. Groen a, b, 1 , Paul W.J. van Vught a , Wouter van Rheenen a , Esther Witteveen a , Michael A. van Es a , R. Jeroen Pasterkamp b , Leonard H. van den Berg a, 2 , Jan H. Veldink a, * , 2 a Rudolf Magnus Institute of Neuroscience, Department of Neurology, University Medical Center Utrecht, Utrecht, the Netherlands b Rudolf Magnus Institute of Neuroscience, Department of Neuroscience and Pharmacology, University Medical Center Utrecht, Utrecht, the Netherlands article info Article history: Received 28 June 2012 Received in revised form 19 September 2012 Accepted 26 September 2012 Keywords: Amyotrophic lateral sclerosis Genome-wide association studies C9ORF72 UNC13A Mutation analysis Genetics abstract Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease that causes progressive muscle weakness, eventually resulting in death because of respiratory failure. Genetic variants are thought to predispose to the disease. A recent, large, genome-wide association study identified 2 loci that increase susceptibility to ALS. These 2 loci on chromosomes 9 and 19 consist of 4 genes: UNC13a, IFNK, MOBKL2b, and C9ORF72. A hexanucleotide repeat expansion in the noncoding region of C9ORF72 was recently identified as the cause of chromosome 9-linked ALS-FTD (frontotemporal dementia). In this study, our aim was to determine whether the coding regions of these genes harbor rare, nonsynonymous variants that playa role in ALS pathogenesis. In DNA from 1019 sporadic ALS patients and 1103 control subjects of Dutch descent, we performed a mutation screening analysis in the coding region of these 4 genes by resequencing the exons. A total of 16 amino acid-changing rare variations were identified, 11 in UNC13a and 5 on chromosome 9. Some of these were unique to ALS, but were detected in a single patient. None of the genes showed significant enrichment of rare variants in the coding sequence. Rare variants in the coding region of UNC13a, IFNK, MOBKL2b, and C9ORF72 are unlikely to be a genetic cause of ALS. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Amyotrophic lateral sclerosis (ALS) is an adult onset neurological disease characterized by degeneration of motor neurons in cortex, brain stem, and spinal cord. Initial manifestations include muscle weakness in limbs and difficulties with speech and swallowing. Patients usually die between 2 and 5 years after symptom onset, usually because of respiratory failure. There is no effective therapy and the only drug available to patients is riluzole, which extends life by 3e6 months (Kiernan et al., 2011). In approximately 10% of the cases, there is a family history of ALS (fALS), and the remaining 90% is considered to suffer from sporadic ALS. Several genes have been linked to fALS, including SOD1 , TARDBP , VAPB, OPTN, VCP, UBQLN2, and FUS, with variable frequen- cies depending on the geographical location of investigated samples (Koppers et al., 2012; van Es et al., 2010). Sporadic ALS is a complex disease, with both genetic and envi- ronmental factors contributing to pathogenesis. To date, the only well established genetic factors in sporadic ALS are rare variants in the coding sequence of several fALS genes and more recently the repeat expansion in C9ORF72 (Majounie et al., 2012). Single nucle- otide polymorphisms and other common structural variants have been reported to be associated with ALS, but often fail to replicate in independent populations (Dion et al., 2009). Recently, large genome-wide association studies have discov- ered 2 significant loci associated with ALS (Shatunov et al., 2010; van Es et al., 2009). The associated single nucleotide poly- morphisms are located in genomic regions that comprise a total of 4 genes: UNC13a on chromosome 19, and IFNK, MOBKL2b, and C9ORF72 on chromosome 9. These findings were replicated in an independent cohort of UK and Italian patients (Shatunov et al., 2010) and more recently in an independent Dutch sample (Diekstra et al., 2012). The association with chromosome 9 was also replicated in a Finnish cohort (Laaksovirta et al., 2010). Recently, a hexanucleotide repeat expansion in the noncoding region of C9ORF72 was identified as the genetic cause of chromosome 9-linked ALS-FTD (frontotemporal dementia) (Dejesus-Hernandez et al., 2011; Renton et al., 2011). Repeat expansions were also identified in approximately 4%e8% of sporadic ALS patients, which * Corresponding author at: Department of Neurology, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands. Tel.: þ31 88 7557992; fax: þ31 88 7552100. E-mail address: j.h.veldink@umcutrecht.nl (J.H. Veldink). 1 These authors contributed equally. 2 J.H.V. and L.H.v.d.B. are the lead investigators and contributed equally. Contents lists available at SciVerse ScienceDirect Neurobiology of Aging journal homepage: www.elsevier.com/locate/neuaging 0197-4580/$ e see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.neurobiolaging.2012.09.018 Neurobiology of Aging xxx (2012) 1e3