1. ¹Institute for Human Genetics, Johannes Gutenberg University Mainz, Mainz, Germany
2. ²Human Genetic Practice, Berlin, Germany
3. ³Institute for Medical Genetics, Faculty of Medicine, Charite, Berlin, Germany
4. ⁴Human Genetic Practice, Cottbus, Germany

Correspondence: Professor T Haaf, Institute for Human Genetics, Mainz University, School of Medicine, Langenbeckstrasse 1, Bldg 601, Mainz 55131, Germany. Tel: +49 6131 175790; Fax: +49 6131 175690; E-mail: haaf@humgen.klinik.uni-mainz.de

Received 7 February 2006; Revised 30 December 2006; Accepted 19 January 2007; Published online 28 February 2007.

Abstract

A boy with severe mental retardation, funnel chest, bell-shaped thorax, and hexadactyly of both feet was found to have a balanced de novo t(12;17)(p13.3;q21.3) translocation. FISH with BAC clones and long-range PCR products assessed in the human genome sequence localized the breakpoint on chromosome 17q21.3 to a 21-kb segment that lies <30 kb upstream of the HOXB gene cluster and immediately adjacent to the 3' end of the TTLL6 gene. The breakpoint on chromosome 12 occurred within telomeric hexamer repeats and, therefore, is not likely to affect gene function directly. We propose that juxtaposition of the HOXB cluster to a repetitive DNA domain and/or separation from required cis-regulatory elements gave rise to a position effect.