X-linked Cornelia de Lange syndrome owing to SMC1L1 mutations Antonio Musio 1 , Angelo Selicorni 2 , Maria Luisa Focarelli 1 , Cristina Gervasini 3 , Donatella Milani 2 , Silvia Russo 4 , Paolo Vezzoni 1 & Lidia Larizza 3,4 Cornelia de Lange syndrome is a multisystem developmental disorder characterized by facial dysmorphisms, upper limb abnormalities, growth delay and cognitive retardation. Mutations in the NIPBL gene, a component of the cohesin complex, account for approximately half of the affected individuals. We report here that mutations in SMC1L1 (also known as SMC1), which encodes a different subunit of the cohesin complex, are responsible for CdLS in three male members of an affected family and in one sporadic case. Cornelia de Lange Syndrome (CdLS, MIM 122470) is a clinically heterogeneous developmental disorder characterized by malforma- tions affecting multiple systems. Although classical severe cases of CdLS are easily identified clinically, mild phenotypes are also frequent. Recently, the gene responsible for about half of CdLS cases was identified by two groups 1,2 . This gene, NIPBL (homologous to Scc2 in yeast), codes for a protein that is implicated in chromosome cohesion. The core of the cohesin complex, first identified as respon- sible for chromatid cohesion, includes a heterodimer composed of SMC1 and SMC3, encoded by two members of the ‘structural maintenance of chromosomes’ gene family, and two non-SMC sub- units, Scc1 (in humans, hSCC1 or hRAD21) and Scc3 (in humans, SA1 and SA2). Recent work suggests that these molecules assemble in a tripartite ring-shaped structure that inter- acts with DNA chains 3 . In particular, in this recently proposed model, the two SMC sub- units assume a rod-shaped conformation self-folded by antiparallel coiled-coil interac- tion and associate with each other through a ‘hinge’ domain positioned at one end of the rod, resulting in a V-shaped dimer. At the opposite end, each SMC molecule has a ‘head’ domain, whose engagement could ‘close’ or ‘open’ the ring: this region is also the site of interaction with Scc1 and Scc3 (ref. 4). However, at least three other molecules contribute to the correct function of the cohesin complex: Scc2 (Nipped-B in Drosophila melanogaster; encoded by NIPBL in humans), Eco1 (encoded by ESCO2 in humans) and Pds5, which probably have a role in cohesin loading, chromatin interaction and/or cohesion maintenance 4 . Notably, ESCO2 has been found to be mutated in two human developmental disorders that share many features with CdLS: Roberts syndrome (MIM 268300) and SC phocomelia (MIM 269000) 5,6 . Owing to the frequent severe presentation of CdLS, most cases arise sporadically as a consequence of de novo mutations, whereas the often milder familial cases are rare. Extensive analysis of a large series of individuals in one study clearly showed that single-allele mutations at the NIPBL locus accounted for 56 out of 120 CdLS cases 7 , although some mutations might have escaped detection using standard analysis. Although the NIPBL gene is associated with the cohesin complex in many organisms, its role in activation of homeobox genes in D. melanogaster has raised the possibility that this gene has an additional function in regulating genes that are activated at specific stages of development 8 . SMC1 seems to have multiple roles that differ from those of the other cohesin complex factors: besides having a structural function, it is involved in genome stability 9 , DNA repair and recombination 10 and gene expression 11 . With these considerations in mind, it was particularly attractive to investigate whether SMC1L1 might be responsible for CdLS. We recruited 53 unrelated and four related individuals with a consistent diagnosis of CdLS, encompassing the entire spectrum of phenotypes, which varies widely 12 (Supplementary Methods online). We screened them using denaturing HPLC and sequencing the complete coding sequence of the NIPBL gene. We found pathogenetic NIPBL mutations in 24 of them, whereas the remaining 33 cases did not bear any mutation. Among these 33 individuals, there was only one instance of familiarity, with two male siblings, their mother and a first cousin affected. We excluded NIPBL involvement in this family not only by © 2006 Nature Publishing Group http://www.nature.com/naturegenetics a b c d e Figure 1 Typical facial phenotypes of the evaluated individuals at the last clinical examination. (a) Individual III-4. (b) Individual III-3. (c) Individual II-4. (d) Individual II-3 (from family 2). (e) Individual III-2. We obtained informed consent from these individuals or their parents for publication of photographs. Received 7 December 2005; accepted 10 March 2006; published online 9 April 2006; doi:10.1038/ng1779 1 Institute of Biomedical Technologies, Human Genome Department, Consiglio Nazionale delle Ricerche, Via Fratelli Cervi, 93, 20090 Segrate, Italy. 2 I Clinica Pediatrica, Universita ` degli Studi di Milano, Fondazione Policlinico, Via della Commenda, 9, 20122 Milan, Italy. 3 Division of Medical Genetics, San Paolo School of Medicine, University of Milan, Via A. di Rudinı`, 8, 20142 Milan, Italy. 4 Laboratory of Molecular Genetics, Istituto Auxologico Italiano, via Zucchi 18, 20095 Milan, Italy. Correspondence should be addressed to A.M. (antonio.musio@itb.cnr.it). NATURE GENETICS ADVANCE ONLINE PUBLICATION 1 BRIEF COMMUNICATIONS