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Multicolour FISH fine mapping unravels an insertion as a complex chromosomal rearrangement involving six breakpoints and a 5.89 Mb large deletion
  1. J Kraus1,
  2. M Cohen2,
  3. M R Speicher1
  1. 1Institut für Humangenetik, Technische Universität München and GSF, Trogerstrasse 32, D-81675 München, Germany
  2. 2Kinderzentrum München, Heiglhofstr. 63, D-81377 München, Germany
  1. Correspondence to:
 Dr M R Speicher, Institut für Humangenetik, TU München, Trogerstrasse 32, D-81675 München, Germany; 

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Occam’s razor is a logical principle attributed to the medieval philosopher William of Occam. It is also referred to as the principle of parsimony, which states that one should always choose the simplest explanation of a phenomenon.1 This principle is usually applied in chromosome banding analyses, as interpretations with a minimal number of breakpoints are usually favoured to explain observed chromosomal rearrangements. However, here we present a case in which this principle was not applicable.

In a patient seen because of developmental delay and several craniofacial dysmorphic features, chromosome analysis showed an insertion of 7q material into the short arm of one chromosome 5. This seemingly simple rearrangement was unravelled by advanced molecular cytogenetic tools to be in fact a highly complex rearrangement. We present the clinical data and describe the entire molecular cytogenetic examinations, which included seven fluorochrome multiplex fluorescence in situ hybridisation (M-FISH)2 and the application of 61 BAC probes for the fine mapping of breakpoints within kb resolution. Altogether we identified six breakpoints and found inside the inserted material a deletion with a size of 5.89 Mb.

This is a case that shows that apparent balanced chromosomal rearrangements, which are difficult to corroborate with clinical findings, should be double checked by high resolution approaches.


The patient was born as the second child to a 32 year old mother and her non-consanguineous 39 year old husband after an uneventful pregnancy. Birth weight (2690 g, >10th centile), length (53 cm, >90th centile), and head circumference (33 cm, 25th centile) were within the normal range. She had a 4 year old, healthy sister.

At the age of 4 months insufficient control of head movement was noted. Physiotherapy treatment was started at the age of 7 months. At 10 months the patient could sit unassisted and spoke several syllables. …

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