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Partial hexasomy 15pter→15q13 including SNRPN and D15S10: first molecular cytogenetically proven case report
  1. A Nietzel1,
  2. B Albrecht2,
  3. H Starke1,
  4. A Heller1,
  5. G Gillessen-Kaesbach2,
  6. U Claussen1,
  7. T Liehr1
  1. 1Institut für Humangenetik und Anthropologie, 07740 Jena, Germany
  2. 2Institut für Humangenetik und Anthropologie, Universitätsklinikum, 45122 Essen, Germany
  1. Correspondence to:
 Dr T Liehr, Institut für Humangenetik und Anthropologie, Postfach, D-07740 Jena, Germany;
 i8lith{at}mti.uni-jena.de

https://doi.org/10.1136/jmg.40.3.e28

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    Isodicentric chromosomes 15 (idic(15) or inv dup(15) chromosomes) are the most common supernumerary marker chromosome (SMC) in humans.1 Buckton et al2 found that 0.24% of newborns had a SMC, of which 50% could be described as idic(15). The presence of such chromosomes is usually associated with mental retardation, developmental delay, epilepsy, and behavioural problems like autism.3 It is possible that the clinical severity depends on the size of the SMC and its euchromatic material, for example, almost no clinical signs were detectable in a case with idic(15)(pter→q12),4 while a severe phenotype including all typical clinical signs was present in a patient with the karyotype 47,+idic(15)(pter→q13).3,5,6 However, there are also reports which show an inconsistent relationship between marker size, gene dosage, and severity of the phenotype.7,8 In the study of Mignon et al,8 in all 16 cases studied the derivative chromosomes 15 were of maternal origin with an identical methylation profile, and neither imprinting nor methylation could explain the phenotypic variability. Partial trisomy of 15q11-q14 resulting from intrachromosomal duplication of chromosome 15q11-q14 has also been reported.9,10

    Key points

    • We report on a case of a partial hexasomy 15pter→15q13 including the loci SNRPN and D15S10 as shown by different fluorescence in situ hybridisation (FISH) methods.

    • The newborn girl presented with postaxial polydactyly of both hands and one foot, muscular hypotonia, and a heart defect. She developed seizures and at the age of 3 years she had severe developmental delay, microcephaly, and pachygyria.

    • The karyotype was described as 48,XX,+2mar after GTG banding. The origin of the two additional identical supernumerary marker chromosomes (SMC) was characterised using a centromere specific multicolour FISH (cenM FISH) approach. Multicolour banding (MCB) and two probes specific for the Prader-Willi-syndrome chromosome region in 15q13 defined the …

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