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Rare polymorphic variants of the AGTR2 gene in boys with non-specific mental retardation
  1. T Bienvenu1,
  2. K Poirier1,
  3. H Van Esch1,4,
  4. B Hamel2,
  5. C Moraine3,
  6. J P Fryns4,
  7. H H Ropers5,
  8. C Beldjord1,
  9. H G Yntema2,
  10. J Chelly1
  1. 1Institut Cochin - INSERM U567, Université Paris V René Descartes, IFR116, 24 rue du Fbg St Jacques, 75014 Paris, France
  2. 2Department of Human Genetics, University Hospital, Nijmegen, The Netherlands
  3. 3Service de Génétique - INSERM U316, CHU Bretonneau, Tours, France
  4. 4Centre for Human Genetics, Clinical Genetics Unit, Leuven, Belgium
  5. 5Max Planck Institut für Molekulare Genetik, Berlin, Germany
  1. Correspondence to:
 Dr T Bienvenu, Institut Cochin - INSERM U567, Université Paris V René Descartes, IFR116, 24 rue du Fbg St Jacques, 75014 Paris, France; 

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Mental retardation (MR) is a frequent cause of serious handicap in children and young adults. It is defined as an overall intelligence quotient (IQ) lower than 70 associated with functional deficits in adaptive behaviour (such as daily living skills, social skills, and communication), with an onset before 18 years.1,2 Moderate to severe MR (IQ<50) is estimated to affect 0.4–0.8% of the population and the prevalence increases to 2% if mild MR (50<IQ<70) is included, although these estimates vary widely between different epidemiological studies.2 The underlying causes of MR are extremely heterogeneous. They include non-genetic factors, which act prenatally or during early infancy and cause brain injury, as well as established genetic causes. The prevalence of X linked mental retardation (XLMR) has been estimated as 1.8/1000 males with a carrier frequency of 2.4/1000 females.3 Historically, XLMR is classified as syndromic (MRXS) or as non-specific forms (MRX). Recently, absence of expression of the angiotensin II specific receptor (AGTR2) gene was found in a female patient with moderately severe mental retardation (IQ=44) and a balanced X;7 chromosome translocation.4 Additionally, eight of 590 unrelated male patients with MR were found to have sequence changes in the AGTR2 gene. A deletion of one thymine (T) within a string of eight Ts has been identified in a familial form and in a sporadic case with MR, and three different missense mutations have been found in seven sporadic patients with MR (G21V, R324Q, and I337V). Five of these patients had seizures, two showed autistic behaviour, and only one patient suffered from hypertension. Some patients were reported to have additional clinical findings, but these were not further specified.4 These findings prompted us to analyse extensively the AGTR2 gene in X linked MR families collected by the European XLMR Consortium and in sporadic …

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