© 2001 Oxford University Press Human Molecular Genetics, 2001, Vol. 10, No. 9 941–946 MECP2 is highly mutated in X-linked mental retardation Philippe Couvert 1 , Thierry Bienvenu 1,2 , Cecile Aquaviva 2 , Karine Poirier 1 , Claude Moraine 3 , Chantal Gendrot 3 , Alain Verloes 4 , Christian Andrès 3 , Anne Celine Le Fevre 2 , Isabelle Souville 2 , Julie Steffann 2 , Vincent des Portes 1 , Hans-Hilger Ropers 5 , Helger G. Yntema 6 , Jean-Pierre Fryns 7 , Sylvain Briault 3 , Jamel Chelly 1,+ and Beldjord Cherif 1,2 1 INSERM Unité 129-ICGM, CHU Cochin 24 Rue du Faubourg Saint Jacques, 75014 Paris, France, 2 Laboratoire de Biochimie et Génétique Moléculaire, CHU Cochin, Paris, France, 3 CHU de Tours, Service de Génétique, Hopital Bretonneau, 37044 Tours Cedex, France, 4 Centre Universitaire Wallon de Génétique, CUWG CHU Sart Tilman Domaine Universitaire, Liège B-4000, Belgium, 5 Max-Plank-Institute for Molecular Genetics, Ihnestrasse 73, Berlin-Dahlem, Germany, 6 University Hospital Nijmegen, 417 Department of Human Genetics, 6500 HB Nijmegen, The Netherlands and 7 Center for Human Genetics, Clinical Genetics University, UZ Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium Received 3 January 2001; Revised and Accepted 22 February 2001 Following the recent discovery that the methyl-CpG binding protein 2 (MECP2) gene located on Xq28 is involved in Rett syndrome (RTT), a wild spectrum of phenotypes, including mental handicap, has been shown to be associated with mutations in MECP2. These findings, with the compelling genetic evidence suggesting the presence in Xq28 of additional genes besides RabGDI1 and FMR2 involved in non-specific X-linked mental retardation (MRX), prompted us to investigate MECP2 in MRX families. Two novel mutations, not found in RTT, were identified. The first mutation, an E137G, was identified in the MRX16 family, and the second, R167W, was identified in a new mental retardation (MR) family shown to be linked to Xq28. In view of these data, we screened MECP2 in a cohort of 185 patients found negative for the expansions across the FRAXA CGG repeat and reported the identifica- tion of mutations in four sporadic cases of MR. One of the mutations, A140V, which we found in two patients, has been described previously, whereas the two others, P399L and R453Q, are novel muta- tions. In addition to the results demonstrating the involvement of MECP2 in MRX, this study shows that the frequency of mutations in MECP2 in the mentally retarded population screened for the fragile X syndrome is comparable to the frequency of the CGG expansions in FMR1. Therefore, implementa- tion of systematic screening of MECP2 in MR patients should result in significant progress in the field of molecular diagnosis and genetic counseling of mental handicap. INTRODUCTION The MECP2 gene, located in Xq28, comprises three coding exons and encodes a 486 amino acid protein that was identified in 1992 based on its selective binding to methylated CpG dinucleotides in mammalian genomic DNA (1). It is widely expressed and alternative polyadenylation in the 3′-UTR results in a highly expressed 10 kb transcript in the fetal brain and a 5 kb transcript in the adult brain (2). MeCP2 contains two functional domains, an 85 amino acid methyl-cytosine-binding domain (MBD) that binds to DNA bearing one or more symmetrically methylated CpGs, and a 104 amino acid tran- scriptional repression domain (TRD). The TRD interacts with the transcriptional corepressor SIN3A to recruit histone deacetylases. Interaction between this transcription repressor complex and chromatin-bound MeCP2 causes deacetylation of core histones resulting in transcriptional repression (1,3–5). Recently, mutations in the MECP2 gene have been found in patients with Rett syndrome (RTT), a severe neurological condition occurring almost exclusively in females (6). Further reports showed that mutations in MECP2 account for 70–80% of RTT cases and are also involved in a broad spectrum of phenotypes, including mild intellectual difficulties in females and neonatal encephalopathy in males surviving to birth (7–16). More recently, two interesting mutations associated with severe forms of mental retardation (MR) were reported in two families. The first, an A140V mutation, was identified in a small family in which two females are affected with mild MR and four males with severe MR (17). The second mutation, E406X, was identified in a three-generation family in which two affected males exhibit severe MR and progressive spasticity (18). Together, these findings strongly suggested that the MECP2 gene is a potential candidate for non-specific X-linked MR (MRX). In this study, we report for the first time mutations in MECP2 associated with recessive MRX in families where linkage studies excluded the whole X chromosome except an + To whom correspondence should be addressed. Tel: +33 1 44 41 24 10; Fax: +33 1 44 41 24 21; Email: chelly@icgm.cochin.inserm.fr