ARTICLE Temtamy Preaxial Brachydactyly Syndrome Is Caused by Loss-of-Function Mutations in Chondroitin Synthase 1, a Potential Target of BMP Signaling Yun Li, 1,2,15 Kathrin Laue, 3,15 Samia Temtamy, 4 Mona Aglan, 4 L. Damla Kotan, 5 Go ¨khan Yigit, 1,2 Husniye Canan, 6 Barbara Pawlik, 1,2 Gudrun Nu ¨ rnberg, 1,7,8 Emma L. Wakeling, 9 Oliver W. Quarrell, 10 Ingelore Baessmann, 7 Matthew B. Lanktree, 11 Mustafa Yilmaz, 12 Robert A. Hegele, 11 Khalda Amr, 4 Klaus W. May, 13 Peter Nu ¨rnberg, 1,7,8 A. Kemal Topaloglu, 14 Matthias Hammerschmidt, 1,3,8, * and Bernd Wollnik 1,2,8, * Altered Bone Morphogenetic Protein (BMP) signaling leads to multiple developmental defects, including brachydactyly and deafness. Here we identify chondroitin synthase 1 (CHSY1) as a potential mediator of BMP effects. We show that loss of human CHSY1 function causes autosomal-recessive Temtamy preaxial brachydactyly syndrome (TPBS), mainly characterized by limb malformations, short stature, and hearing loss. After mapping the TPBS locus to chromosome 15q26-qterm, we identified causative mutations in five consan- guineous TPBS families. In zebrafish, antisense-mediated chsy1 knockdown causes defects in multiple developmental processes, some of which are likely to also be causative in the etiology of TPBS. In the inner ears of zebrafish larvae, chsy1 is expressed similarly to the BMP inhibitor dan and in a complementary fashion to bmp2b. Furthermore, unrestricted Bmp2b signaling or loss of Dan activity leads to reduced chsy1 expression and, during epithelial morphogenesis, defects similar to those that occur upon Chsy1 inactivation, indicating that Bmp signaling affects inner-ear development by repressing chsy1. In addition, we obtained strikingly similar zebrafish phenotypes after chsy1 overexpression, which might explain why, in humans, brachydactyly can be caused by mutations leading either to loss or to gain of BMP signaling. Introduction Brachydactylies are characterized by finger and toe short- ening caused by short or absent metacarpus or metatarsus and/or phalanges. They can occur either as an isolated trait or as part of a syndrome in combination with other devel- opmental malformations. Recent analyses have identified mutations in components of the Bone Morphogenetic Protein (BMP) signaling pathway or its modulators as the cause of different types of brachydactyly. According to current concepts, loss of BMP signaling, as for example caused by loss-of-function mutations in the BMP ligand GDF5 (MIM 601146) or the GDF5 high-affinity receptor BMPR1B (MIM 603248), leads to reduced bone formation and brachydactyly type A2 (BDA2 [MIM 112600]) or type C (BDAC [MIM 113100]), 1 whereas gain of BMP signaling, as manifested by loss-of-function mutations in the BMP inhibitor Noggin (MIM 602991), can result in compro- mised joint formation between the different bony hand and foot elements and in the development of symphalan- gism (SYM1 [MIM 185800]) and/or multiple synostosis syndrome (SYNS1 [MIM 186500]). 2 However, the effects of BMP signaling seem to be more complex and subject to intensive fine tuning. For instance, in addition to being caused by loss of GDF5 activity, BDA2 can also be caused by gain of BMP2 signaling, and brachydactyly type B2 (BDB2 [MIM 611377]) can be caused by missense mutations in Noggin (Mundlos 1 and references therein). Similarly, both GDF5 and Noggin mutations are linked to deafness in SYNS1. 3 In light of this, the exact roles of BMP signaling and the nature of mediators accounting for the differential effects remain largely obscure. The Temtamy preaxial brachydactyly syndrome (TPBS [MIM 605282]) is an autosomal-recessive congenital syn- drome mainly characterized by bilateral, symmetric pre- axial brachydactyly and hyperphalangism of digits, facial dysmorphism, dental anomalies, sensorineural hearing loss, delayed motor and mental development, and growth retardation. 4 Here we mapped the TPBS locus to chromosome 15q26- qterm and identified causative mutations in CHSY1 (MIM 608183) in five TPBS families. The zebrafish has recently emerged as a suitable animal model for human develop- ment and disease. 5 We show that in developing zebrafish, 1 Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany; 2 Institute of Human Genetics, University Hospital Cologne, Univer- sity of Cologne, Cologne, Germany; 3 Institute of Developmental Biology, University of Cologne, Cologne, Germany; 4 Departments of Clinical and Molec- ular Genetics, Division of Human Genetics and Human Genome Research, National Research Centre, Cairo, Egypt; 5 Department of Biotechnology, Insti- tute of Sciences, Cukurova University, Adana, Turkey; 6 Department of Forensic Medicine, Faculty of Medicine, Cukurova University, Adana, Turkey; 7 Cologne Center for Genomics, University of Cologne, Cologne, Germany; 8 Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany; 9 North West Thames Regional Genetic Service, Harrow, London, UK; 10 Sheffield Clinical Genetics Service, Sheffield Children’s Hospital, Sheffield, UK; 11 Blackburn Cardiovascular Genetics Laboratory, Robarts Research Institute, University of Western Ontario, London, Ontario, Canada; 12 Department of Pediatric Allergy and Immunology, Faculty of Medicine, Cukurova University, Adana, Turkey; 13 Genomatix Software GmbH, Mu ¨ nchen, Germany; 14 Department of Pediatric Endocrinology, Faculty of Medicine, Cukurova University, Adana, Turkey 15 These authors contributed equally to this work *Correspondence: mhammers@uni-koeln.de (M.H.), bwollnik@uni-koeln.de (B.W.) DOI 10.1016/j.ajhg.2010.10.003. Ó2010 by The American Society of Human Genetics. All rights reserved. The American Journal of Human Genetics 87, 757–767, December 10, 2010 757