BRIEF COMMUNICATIONS Senataxin, the ortholog of a yeast RNA helicase, is mutant in ataxia-ocular apraxia 2 Maria-Céu Moreira 1 , Sandra Klur 1 , Mitsunori Watanabe 2 , Andrea H Németh 3 , Isabelle Le Ber 4 , José-Carlos Moniz 5 , Christine Tranchant 6 , Patrick Aubourg 7 , Meriem Tazir 8 , Lüdger Schöls 9 , Massimo Pandolfo 10 , Jörg B Schulz 11 , Jean Pouget 12 , Patrick Calvas 13 , Masami Shizuka-Ikeda 2 , Mikio Shoji 2 , Makoto Tanaka 2 , Louise Izatt 14 , Christopher E Shaw 15 , Abderrahim M’Zahem 16 , Eimear Dunne 3 , Pascale Bomont 1 , Traki Benhassine 17 , Naïma Bouslam 4 , Giovanni Stevanin 4 , Alexis Brice 4 , João Guimarães 18 , Pedro Mendonça 19 , Clara Barbot 20,21 , Paula Coutinho 20,22 , Jorge Sequeiros 20 , Alexandra Dürr 4 , Jean-Marie Warter 6 & Michel Koenig 1 Ataxia-ocular apraxia 2 (AOA2) was recently identified as a new autosomal recessive ataxia. We have now identified causative mutations in 15 families, which allows us to clinically define this entity by onset between 10 and 22 years, cerebellar atrophy, axonal sensorimotor neuropathy, oculomotor apraxia and elevated alpha-fetoprotein (AFP). Ten of the fifteen mutations cause premature termination of a large DEAxQ-box helicase, the human ortholog of yeast Sen1p, involved in RNA maturation and termination. We previously identified a 16-cM interval on chromosome 9q34 associ- ated with an autosomal recessive adolescent-onset cerebellar ataxia seg- regating in two families 1,2 , one with additional oculomotor apraxia 1 and the second with associated elevated serum AFP, immunoglobulins and creatine kinase levels but no oculomotor apraxia 2,3 . We identified nine additional families with ataxia linked to 9q34 by homozygosity mapping (Supplementary Methods online). As most affected individuals had both oculomotor apraxia and elevated AFP levels we assumed that they were affected by the same disorder, which we named AOA2 (OMIM 606002). We identified distal and proximal recombinations in families with two affected individuals (Fig. 1a), localizing the defective gene underlying AOA2 to a 1.1-Mb interval containing 13 genes (Fig. 1b) and three groups of overlapping spliced expressed-sequence tags, which we analyzed for nucleotide changes but found no mutations. We also found that the unspliced mRNA AK024331 overlaps with the KIAA0625 cDNA and is part of a larger transcript overlapping with additional exons on the 5′ side. We obtained an open reading frame of 8,031 nucleotides and 24 exons (Fig. 1c), of which exon 8 was 4,177 nucleotides long. We con- firmed the prediction and size of the transcript by long-range RT-PCR experiments spanning the putative exon 1 and 3′ untranslated region in human fibroblast and lymphoblastoid cell lines (data not shown) and by hybridization of a human northern blot with a probe spanning putative exons 8–24 (Fig. 1d). We also identified an alternative transcript that is 2.4 kb longer, resulting from a second polyadenylation site (human mRNAs AB014525 and AK022902; Fig. 1d). We sequenced exons 1–18 and flanking intronic sequences in fami- lies with ataxia linked to this region and in additional individuals with either AOA or ataxia with elevated AFP levels and found 15 different disease-associated mutations in 15 families (Table 1). Ten of these mutations, including mutations in the two families in whom we first identified AOA2, cause truncation of the protein, indicating that this is the gene underlying AOA2. We found the nonsense mutation R1363X in three unrelated families originating from Portugal, Cabo Verde (once a Portuguese colony) and Spain, suggestive of an Iberian founder event, although recurrent C→T changes on this CpG dinucleotide can- not be formally excluded. Absence of the five missense mutations in 150 unrelated and unaffected individuals sharing the same ethnic origin as the affected individuals indicates that they are not frequent polymor- phisms. Two of the missense mutations were associated with a frameshift mutation inherited from the other parent, and the remain- ing missense mutations were present in the homozygous state in the affected individuals. We identified four variants resulting in amino acid changes and a silent nucleotide change (Table 1) on the normal chro- mosome of healthy siblings or parents from several families, indicating that they were frequent polymorphisms. Before our mapping, the disorders in the different families were con- sidered to be clinically distinct entities. We can now delineate the com- mon clinical phenotype associated with mutant senataxin, illustrating the power of defining disorders by their genetic locus and identified mutations. We considered only those families in whom we had con- firmed mutations when delineating the AOA2 phenotype, as some con- sanguineous families with sporadic affected individuals could show 1 IGBMC (Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, ULP) 67404 Illkirch, C.U. de Strasbourg, France. 2 Gunma University School of Medicine, Maebashi 371-8511, Japan. 3 Wellcome Trust Centre for Human Genetics, Oxford OX3 7BN, UK. 4 Institut National de la Santé et de la Recherche Médicale U289 and Département de Génétique, Cytogénétique et Embryologie, Hôpital de la Salpêtrière, AP-HP, 75651 Paris, France. 5 Hospital Sto. António dos Capuchos, Lisboa, Portugal. 6 Hôpitaux Universitaires de Strasbourg, 67091 Strasbourg, France. 7 Institut National de la Santé et de la Recherche Médicale U342, Hôpital Saint Vincent de Paul, 75675 Paris, France. 8 Centre Hospitalier Universitaire Mustapha, Algier 16000, Algeria. 9 Department of Neurology, St. Josef Hospital, Ruhr-University Bochum, Germany. 10 Université Libre de Bruxelles-Hôpital Erasme, 1070 Brussels, Belgium. 11 Department of General Neurology, Center of Neurology and Hertie Institute for Clinical Brain Research, University of Tübingen, 72076 Tübingen, Germany. 12 Hôpital de la Timone Adultes, 13385 Marseille, France. 13 Hôpital Purpan, 31059 Toulouse, France. 14 Department of Clinical Genetics, Guy’s Hospital, London SE1 9RT, UK. 15 Guy’s King’s and St Thomas’ School of Medicine and Institute of Psychiatry, King’s College, London, SE5 8AF, UK. 16 Centre Hospitalier Universitaire Ben Badis, Constantine, Algeria. 17 Institut Pasteur d’Alger, Algeria. 18 Hospital de Egas Moniz, Lisboa, Portugal. 19 Department of Hematology, Hospital do Divino Espírito Santo, S. Miguel, Azores, Portugal. 20 UnIGENe - IBMC, ICBAS, Universidade Porto, 4150 – 180 Porto, Portugal. 21 Department of Neuropediatrics, Hospital Maria Pia, 4050 Porto, Portugal. 22 Department of Neurology, Hospital São Sebastião, 4520 Sta. Maria da Feira, Portugal. Correspondence should be addressed to M.K. (mkoenig@igbmc.u-strasbg.fr). Published online 8 February 2004; doi:10.1038/ng1303 NATURE GENETICS VOLUME 36 | NUMBER 3 | MARCH 2004 225 © 2004 Nature Publishing Group http://www.nature.com/naturegenetics