Mutations in the EDA gene are responsible for X-linked hypohidrotic ectodermal dysplasia and hypodontia in Chinese kindreds Huali Fan 1 *, Xiaoqian Ye 1 *, Lisong Shi 2 , Wei Yin 1 , Bo Hua 1 , Guangtai Song 3 , Bin Shi 4 , Zhuan Bian 1 1 Key Laboratory for Oral Biomedical Engineering of Ministry of Education, Department of Endodontics, Hospital and School of Stomatology, Wuhan University; 2 Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology and Center for Human Genome Research, Huazhong University of Science and Technology; 3 Department of Pediatric Dentistry, Hospital and School of Stomatology, Wuhan University; 4 Department of Prosthodontics, Hospital and School of Stomatology, Wuhan University, Wuhan, Hubei, China Tooth agenesis affects approximately 2–9% of the pop- ulation (1), making it the most common craniofacial anomaly in humans. The condition may occur as a familial non-syndromic disorder, but may also occur as part of a genetic syndrome (2). X-linked hypohidrotic ectodermal dysplasia (XLHED, OMIM 305100), the most frequent form of hypohidrotic ectodermal dysplasia (HED), is characterized by abnormalities of teeth, hair, and eccrine sweat glands (3, 4). Affected males usually present most or all of the typical phenotypes, including distinctive faces, frontal bossing, brittle and sparse hair, linear wrinkles around eyes, maxillary hypoplasia, Ôsad- dleÕ nose, and prominent lips. Teeth are often missing or misshapen, and the skin is smooth and dry with hypo- hidrosis. In heterozygous female carriers, however, the severity of the disorder varies widely, even within fami- lies. Carriers may exhibit minor to moderate degrees of symptoms, but there are some female carriers who, because of putative random X-chromosome inactivation (lyonization), present no obvious clinical manifestations, which makes an accurate diagnosis difficult (5). The gene responsible for XLHED was localized to Xq12-q13 and has been identified as ectodysplasin A (EDA) (6, 7). Ectodysplasin A is a type II transmembrane protein with a small N-terminal intracellular domain, a larger extracellular domain containing a (Gly-X-Y) 19 collagen-like repeat, and a C-terminal tumor necrosis factor (TNF) homology domain (8, 9). EDA, being a member of the TNF ligand superfamily of genes, contains nine exons and has extensive alternative splicing that leads to various isoforms. The most common EDA splice iso- forms (EDA-A1, 391 amino acids; and EDA-A2, 389 amino acids) promote transcription by binding to distinct receptors (10, 11). That is, EDA-A1 binds to the ecto- dysplasin receptor (EDAR), which interacts with the EDAR-associated death domain (EDARADD) and acti- vates the downstream nuclear factor-jB (NF-jB) kinase signaling pathways. However, EDA-A2 binds to an X- linked EDA-A2 receptor (XEDAR). More than 100 mutations have been reported in the EDA gene (HGMD database: http://www.hgmd.cf. ac.uk/), most of which are localized within exons 1, 3, and 5 and are mainly point mutations, clustering in the four functional domains of EDA. Intragenic insertions or deletions, large deletions including entire exon loss, and complete gene deletion have also been reported (12). So far, 14 different EDA mutations have been reported in Chinese families with XLHED (13–15). In the present study we analysed the EDA gene mutations in four unrelated Chinese families with XLHED and in two Chinese families affected by iso- lated hypodontia with an X-linked recessive trait. Direct sequencing allowed identification of five novel muta- tions and one recurrent mutation. Our results may Fan H, Ye X, Shi L, Yin W, Hua B, Song G, Shi B, Bian Z. Mutations in the EDA gene are responsible for X-linked hypohidrotic ectodermal dysplasia and hypodontia in Chinese kindreds. Eur J Oral Sci 2008; 116: 412–417. Ó 2008 The Authors. Journal compilation Ó 2008 Eur J Oral Sci X-linked hypohidrotic ectodermal dysplasia (XLHED, OMIM 305100) is a rare congenital disorder that results in the defective development of teeth, hair, nails, and eccrine sweat glands. Previous studies found that mutations in the ectodysplasin A (EDA) gene are associated with XLHED. In the present study, we investigated four Chinese families suffering from classical XLHED and investigated two additional families segregating hypodontia in an X-linked recessive manner. Mutations were characterized respectively in the EDA gene in all families, and five of these mutations were found to be novel. Among these mutations, five were missense (c.200A>T, c.463C>T, c.758T>C, c.926T>G, and c.491A>C) and located in the functional domain of EDA, and one was a splice donor site mutation in intron 5 (c.IVS5 + 1- G>A), which may result in an alternative transcript derived from a new cryptic splice site. Our data further confirm that EDA mutations could cause both XLHED and isolated hypodontia and provide evidence that EDA is a strong candidate gene for tooth genesis. Zhuan Bian, Key Laboratory for Oral Biomedical Engineering of Ministry of Education, Hospital and School of Stomatology, Wuhan University, Luoyu Road 237, Wuhan, Hubei, China Telefax: +86–27–87647443 E-mail: bz@whuss.com *These authors contributed equally to the work presented in this article. Key words: EDA mutation; hypodontia; hypohidrotic ectodermal dysplasia; sequencing; X-linked Accepted for publication June 2008 Eur J Oral Sci 2008; 116: 412–417 Printed in Singapore. All rights reserved Ó 2008 The Authors. Journal compilation Ó 2008 Eur J Oral Sci European Journal of Oral Sciences