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Disruption of a new X linked gene highly expressed in brain in a family with two mentally retarded males
  1. V Cantagrel1,*,
  2. A-M Lossi1,*,
  3. S Boulanger2,
  4. D Depetris1,
  5. M-G Mattei1,
  6. J Gecz3,
  7. C E Schwartz4,
  8. L Van Maldergem2,
  9. L Villard1
  1. 1Inserm U491, Faculté de Médecine de La Timone, 27, Bd. Jean Moulin, 13385 Marseille Cedex 5, France
  2. 2Centre de Génétique Humaine, Institut de Pathologie et de Génétique, Loverval, Belgium
  3. 3Department of Genetic Medicine, Women and Children’s Hospital, Adelaide, Australia
  4. 4Greenwood Genetic Center, One Gregor Mendel Circle, Greenwood, SC, USA
  1. Correspondence to:
 Lionel Van Maldergem
 Centre de Génétique Humaine, Institut de Pathologie et de Génétique, Allée des Templiers, 41, B-6280 Loverval, Belgium;


Background: Mental retardation (MR) affects 2–3% of the human population and some of these cases are genetically determined. Although several genes responsible for MR have been identified, many cases have still not been explained.

Methods: We have identified a pericentric inversion of the X chromosome inv(X)(p22.3;q13.2) segregating in a family where two male carriers have severe MR while female carriers are not affected.

Results: The molecular characterisation of this inversion led us to identify two new genes which are disrupted by the breakpoints: KIAA2022 in Xq13.2 and P2RY8 in Xp22.3. These genes were not previously fully characterised in humans. KIAA2022 encodes a protein which lacks significant homology to any other known protein and is highly expressed in the brain. P2RY8 is a member of the purine nucleotide G-protein coupled receptor gene family. It is located in the pseudo-autosomal region of the X chromosome and is not expressed in brain.

Conclusions: Because the haploinsufficiency of P2RY8 in carrier mothers does not have a phenotypic consequence, we propose that the severe MR of the affected males in this family is due to the absence of the KIAA2022 gene product. However, screening 20 probands from X linked MR families did not reveal mutations in KIAA2022. Nonetheless, the high expression of this gene in fetal brain and in the adult cerebral cortex could be consistent with a role in brain development and/or cognitive function.

  • AR, androgen receptor
  • BrdU, 5-bromodeoxyuridine
  • FISH, fluorescent in situ hybridisation
  • MR, mental retardation
  • NS MR, non-syndromic mental retardation
  • NS XLMR, non-syndromic X linked mental retardation
  • PAR1, pseudoautosomal region 1
  • chromosomal rearrangement
  • KIAA2022
  • P2RY8
  • X chromosome
  • X linked mental retardation

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  • * These two authors contributed equally to this work.

  • Financial support to VC from the French Ministry of Research is gratefully acknowledged. This study was supported in part by a grant from NICHD (HD26202) to CES.

  • Conflict of interest: none declared.