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J Med Genet 50:339-344 doi:10.1136/jmedgenet-2012-101477
  • Somatic mosaicism
  • Original article

High rate of mosaicism in individuals with Cornelia de Lange syndrome

  1. Raoul C M Hennekam1,3
  1. 1Department of Pediatrics, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
  2. 2Center for Individuals with Intellectual Disabilities, Prinsenstichting, Purmerend, The Netherlands
  3. 3Department of Clinical Genetics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
  1. Correspondence to Dr Raoul C M Hennekam, Department of Pediatrics, Room H7-237, Academic Medical Center, University of Amsterdam, Meibergdreef 9, Amsterdam 1105 AZ, The Netherlands; r.c.hennekam{at}amc.uva.nl
  • Received 11 December 2012
  • Revised 31 January 2013
  • Accepted 14 February 2013
  • Published Online First 15 March 2013

Abstract

Background Cornelia de Lange syndrome (CdLS) is a well known malformation syndrome for which five causative genes are known, accounting for ∼55–65% of cases. In this study, we hypothesised that mosaicism might explain some of the ∼35–45% of cases without detectable mutation in DNA derived from lymphocytes; we investigated the frequency of NIPBL mutations in buccal cells in individuals negative for mutations in any of the five genes in lymphocytes; and we evaluated the efficiency of obtaining DNA from buccal swabs and the best strategy for optimal mutation detection in CdLS.

Methods Buccal swabs were obtained from eight mutation positive and 13 mutation negative individuals with clinically diagnosed CdLS, following informed consent. We then forwarded instructions and a single mouth swab to the families; if subsequently insufficient DNA was obtained, we re-sent two mouth swabs. Buccal cells were screened for NIPBL mutations using Sanger sequencing techniques.

Results Sufficient DNA for analysis was obtained in 21/22 individuals. In all six tested individuals with a known NIPBL mutation and in two with a known SMC1A mutation, the mutation was confirmed in buccal cells. In 10 of the 13 tested individuals without detectable mutation in lymphocytes a NIPBL mutation could be detected in buccal cells. Clinically there were no significant differences between patients with a germline and mosaic NIPBL mutation.

Conclusions Somatic mosaicism for an NIPBL mutation is frequent (10/44; 23%) clinically in reliably diagnosed CdLS individuals. Obtaining buccal swabs at the time a blood sample is obtained will facilitate adequate molecular analysis of clinically diagnosed CdLS patients.