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Emerging patterns of cryptic chromosomal imbalance in patients with idiopathic mental retardation and multiple congenital anomalies: a new series of 140 patients and review of published reports
  1. B Menten1,*,
  2. N Maas2,*,
  3. B Thienpont2,
  4. K Buysse1,
  5. J Vandesompele1,
  6. C Melotte2,
  7. T de Ravel2,
  8. S Van Vooren3,
  9. I Balikova2,
  10. L Backx2,
  11. S Janssens1,
  12. A De Paepe1,
  13. B De Moor3,
  14. Y Moreau3,
  15. P Marynen4,
  16. J-P Fryns2,
  17. G Mortier1,
  18. K Devriendt2,
  19. F Speleman1,
  20. J R Vermeesch2
  1. 1Centre for Medical Genetics, Ghent University, Ghent, Belgium
  2. 2Centre for Human Genetics, University Hospital Gasthuisberg, Leuven, Belgium
  3. 3ESAT-SISTA, University of Leuven, Leuven, Belgium
  4. 4Flanders Interuniversity Institute for Biotechnology (VIB4), Department of Human Genetics, University of Leuven, Leuven, Belgium
  1. Correspondence to:
 Dr J R Vermeesch
 Centre for Human Genetics, Herestraat 49, 3000 Leuven, Belgium; Joris.Vermeesch{at}


Background: Chromosomal abnormalities are a major cause of mental retardation and multiple congenital anomalies (MCA/MR). Screening for these chromosomal imbalances has mainly been done by standard karyotyping. Previous array CGH studies on selected patients with chromosomal phenotypes and normal karyotypes suggested an incidence of 10–15% of previously unnoticed de novo chromosomal imbalances.

Objective: To report array CGH screening of a series of 140 patients (the largest published so far) with idiopathic MCA/MR but normal karyotype.

Results: Submicroscopic chromosomal imbalances were detected in 28 of the 140 patients (20%) and included 18 deletions, seven duplications, and three unbalanced translocations. Seventeen of 24 imbalances were confirmed de novo and 19 were assumed to be causal. Excluding subtelomeric imbalances, our study identified 11 clinically relevant interstitial submicroscopic imbalances (8%). Taking this and previously reported studies into consideration, array CGH screening with a resolution of at least 1 Mb has been undertaken on 432 patients with MCA/MR. Most imbalances are non-recurrent and spread across the genome. In at least 8.8% of these patients (38 of 432) de novo intrachromosomal alterations have been identified.

Conclusions: Array CGH should be considered an essential aspect of the genetic analysis of patients with MCA/MR. In addition, in the present study three patients were mosaic for a structural chromosome rearrangement. One of these patients had monosomy 7 in as few as 8% of the cells, showing that array CGH allows detection of low grade mosaicisims.

  • BAC, bacterial artificial chromosome
  • CGH, comparative genomic hybridisation
  • CNV, copy number variation
  • MCA/MR, mental retardation and multiple congenital anomalies
  • PAC, P1 derived artificial chromosome
  • RTQ-PCR, real time quantitative polymerase chain reaction
  • array CGH
  • mosaicism
  • mental retardation

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  • Published Online First 20 February 2006

  • * Both authors contributed equally to this work.

  • Conflicts of interest: none declared