American Journal of Medical Genetics 124A:165–169 (2004) Search for Somatic 22q11.2 Deletions in Patients With Conotruncal Heart Defects Anita Rauch, 1 * Michael Hofbeck, 2,3 Robert Cesnjevar, 4 Andreas Koch, 2 Ralf Rauch, 2,3 Gernot Buheitel, 2 Helmut Singer, 2 and Michael Weyand 4 1 Institute of Human Genetics, Friedrich-Alexander University, Erlangen-Nuremberg, Germany 2 Department of Pedatric Cardiology, Friedrich-Alexander University, Erlangen-Nuremberg, Germany 3 Department of Pedatric Cardiology, University of Tuebingen, Germany 4 Department of Heart Surgery, Friedrich-Alexander University, Erlangen-Nuremberg, Germany A wide range of clinical variability in patients with 22q11.2 deletions has been demon- strated in numerous studies. Nevertheless, it is still an open question if major genetic factors contribute to clinical expression. Therefore one aim of this study was to inves- tigate, if patients with 22q11.2 deletion and conotruncal heart defects show a ‘‘second hit’’ somatic 22q11.2 deletion in tissue from the conotruncus, heart vessels or thymus. The second aim was to analyse patients with conotruncal heart defects without 22q11.2 deletion in blood cells for somatic deletion mosaicism. We were able to study tissue samples from heart surgery from 23 patients, 9 of whom had 22q11 deletions by FISH anal- ysis on metaphase spreads from peripheral lymphocytes. Analysis of 18 polymorphic markers from the 22q11.2 region in DNA prepared from thymus and/or heart vessels and/or conotruncus tissue and peripheral lymphocytes in each patient did not show any allelic loss. Thus somatic 22q11.2 dele- tions apparently do not play a major role in conotruncal heart defects in patients with or without germ line 22q11.2 deletion. ß 2003 Wiley-Liss, Inc. KEY WORDS: modifier; 22q11.2 deletion; somatic deletion; congenital heart defects; DiGeorge syn- drome; VCFS INTRODUCTION Deletion 22q11.2 is a major cause of congenital heart disease (CHD), accounting for about 5% of all CHD [Wilson et al., 1994], up to 15% of conotruncal CHD and up to 20% in foetuses with CHD. However, despite of a common deletion size of 3 Mb patients with a 22q11.2 deletion have a highly variable phenotype [Carlson et al., 1997b]. The underlying mechanism is still an open question, although imprinting, unmasking of recessive mutations by hemizygosity, unbalanced regulatory effects, a second-hit theory and environmental factors have been considered as modifying factors [Hall, 1993; Dallapiccola et al., 1996; Hatchwell, 1996]. As both, the common and the atypical deletions are mediated by several low copy repeats within the region [Edelmann et al., 1999a,b; Rauch et al., 1999; Saitta et al., 1999; Shaikh et al., 2001; Garcia-Minaur et al., 2002], our hypothesis was that an additional somatic 22q11.2 deletion might be a frequent event, modifying the pheno- type in terms of a second-hit-theory. Furthermore somatic 22q11.2 deletions may explain atypical pheno- types in patients with CHD [Consevage et al., 1996]. To prove these two hypotheses, we analysed 38 probes from thymus and/or heart tissue for somatic 22q11.2 deletions from 23 patients with conotruncal CHD. MATERIALS AND METHODS We analysed children with congenital conotruncal heart defects undergoing heart surgery whose parents had agreed to a collection and study of tissue if available during surgery. To determine germ line 22q11.2 status, FISH analysis was performed on metaphase spreads from peripheral blood cells with 10 DNA probes covering the common and atypical deletion regions (Fig. 1): 6E8 (D22S427) [Edelmann et al., 1999a], 51H3 (D22S1649) [Carlson et al., 1997a], 70A2 (D22S1694) [Carlson et al., 1997a], Pac 140D4 (HIRA) [Carlson et al., 1997a], co23 (UFD1L) [Pizzuti et al., 1997], D0832 (COMT) [Carlson et al., 1997a], 48c12 (D22S264) [Edelmann et al., 1999b], cHKAD26 (D22S935) [Kurahashi et al., 1994; Kurahashi et al., 1997], 109G12 (109G12) [Edelmann et al., 1999a], BAC 438P22 (D22S425) [Rauch et al., 1999] (Fig. 1). Grant sponsor: Deutsche Forschungsgemeinschaft; Grant number: RA 833/4-1. *Correspondence to: Dr. Anita Rauch, Institute of Human Genetics, Schwabachanlage 10, 91054 Erlangen, Germany. E-mail: arauch@humgenet.uni-erlangen.de Received 11 February 2003; Accepted 8 April 2003 DOI 10.1002/ajmg.a.20323 ß 2003 Wiley-Liss, Inc.