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J Med Genet 43:180-186 doi:10.1136/jmg.2005.032268
  • Letters to JMG

Array-CGH detection of micro rearrangements in mentally retarded individuals: clinical significance of imbalances present both in affected children and normal parents

  1. C Rosenberg1,*,
  2. J Knijnenburg1,*,
  3. E Bakker2,
  4. A M Vianna-Morgante3,
  5. W Sloos1,
  6. P A Otto3,
  7. M Kriek2,
  8. K Hansson2,
  9. A C V Krepischi-Santos3,
  10. H Fiegler4,
  11. N P Carter4,
  12. E K Bijlsma2,
  13. A van Haeringen2,
  14. K Szuhai1,
  15. H J Tanke1
  1. 1Laboratory of Cytochemistry and Cytometry, Department of Molecular Cell Biology, Leiden University Medical Centre, Leiden, Netherlands
  2. 2Department of Human and Clinical Genetics, Leiden University Medical Centre
  3. 3Department of Genetics and Evolutionary Biology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil
  4. 4The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
  1. Correspondence to:
 Dr Carla Rosenberg
 Departamento de Biologia, Instituto de Biociências – Universidade de São Paulo, CP 11461-São Paulo, Brazil; carlarosenberg45{at}aol.com
  • Received 20 February 2005
  • Accepted 17 June 2005
  • Revised 16 June 2005
  • Published Online First 24 June 2005

Abstract

Background: The underlying causes of mental retardation remain unknown in about half the cases. Recent array-CGH studies demonstrated cryptic imbalances in about 25% of patients previously thought to be chromosomally normal.

Objective and methods: Array-CGH with approximately 3500 large insert clones spaced at ∼1 Mb intervals was used to investigate DNA copy number changes in 81 mentally impaired individuals.

Results: Imbalances never observed in control chromosomes were detected in 20 patients (25%): seven were de novo, nine were inherited, and four could not have their origin determined. Six other alterations detected by array were disregarded because they were shown by FISH either to hybridise to both homologues similarly in a presumptive deletion (one case) or to involve clones that hybridised to multiple sites (five cases). All de novo imbalances were assumed to be causally related to the abnormal phenotypes. Among the others, a causal relation between the rearrangements and an aberrant phenotype could be inferred in six cases, including two imbalances of the X chromosome, where the associated clinical features segregated as X linked recessive traits.

Conclusions: In all, 13 of 81 patients (16%) were found to have chromosomal imbalances probably related to their clinical features. The clinical significance of the seven remaining imbalances remains unclear. The limited ability to differentiate between inherited copy number variations which cause abnormal phenotypes and rare variants unrelated to clinical alterations currently constitutes a limitation in the use of CGH-microarray for guiding genetic counselling.

Footnotes

  • * These authors contributed equally to the paper

  • Conflicts of interest: none declared

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