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  • Mosaicism del(8p)/inv dup(8p) in a dysmorphic female infant: a mosaic formed by a meiotic error at the 8p OR gene and an independent terminal deletion event

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Mosaicism del(8p)/inv dup(8p) in a dysmorphic female infant: a mosaic formed by a meiotic error at the 8p OR gene and an independent terminal deletion event
  1. J R Vermeesch1,
  2. R Thoelen1,
  3. I Salden1,
  4. M Raes2,
  5. G Matthijs1,
  6. J-P Fryns1
  1. 1Centre of Human Genetics, University Hospital Gasthuisberg, University of Leuven, Leuven, Belgium
  2. 2Department of Paediatrics, Virga-Jesse Hospital, Hasselt, Belgium
  1. Correspondence to:
 Dr J R Vermeesch, Centre for Human Genetics, Herestraat 49, 3000 Leuven, Belgium; 
 Joris.Vermeesch{at}med.kuleuven.ac.be

https://doi.org/10.1136/jmg.40.8.e93

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    Various chromosomal rearrangements are associated with the distal 8p region. Among them are the inv dup(8p),1 del(8p22),2–5 and del(8)(pter).6 The cardinal phenotypic features of the inv dup(8p) are brain malformations, severe mental retardation with specific involvement of speech, and minor facial dysmorphisms.7 Deletions (8p22) are associated with congenital heart malformations, thought to be caused by haploinsufficiency of GATA4.2 Other features are microcephaly, intrauterine growth retardation, mental retardation, and a characteristic hyperactive impulsive behaviour. The patients with del(8p) present with variable severe malformations dependent on the size of the deletion. The largest terminal 8p deletion which has been detected in a liveborn is del(8)(pter→21.1).8

    Molecular analysis of both 8p duplications and 8p interstitial deletions showed that all cases shared similar chromosomal break points. This finding led to the hypothesis that these rearrangements were caused by ectopic recombination at misaligned duplicons. Recently, Giglio et al4 showed the presence of olfactory gene clusters (OR clusters) at the sites where the interstitial 8p deletions occur. Whereas these interstitial deletions could thus be explained by misalignments of the OR clusters during meiosis, they also presented an elegant explanation for the origin of the 8p duplications. An inversion polymorphism between these OR clusters, present in 20% of the population, abrogates correct pairing between the OR clusters which causes susceptibility for an intrachromosomal crossover between the OR repeats. Ectopic recombination at these sites can lead to a dicentric intermediate which on breakage can lead to a duplicated chromosome 8p, the inv dup(8p). The complement of this breakage event was speculated to be a terminal deleted chromosome del(8p).

    In this paper we describe a girl with a mosaic del(8p)/inv dup(8p) in blood lymphocytes. Mosaics with two cell lines carrying two different rearranged chromosomes are extremely rare. Two reports describe the …

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