MG-122 Cytogenetic characterisation of 3 small supernumerary chromosomal markers in a 1 year-old girl

Abstract

Background The frequency of small supernumerary chromosomal markers (sSCM) are estimated to be ˜0.03–0.15% and are not necessarily always associated with clinical phenotypes. Their characterisation is important since they can be helpful in establishing phenotype-genotype correlations, which is essential for genetic counselling. Objectives Cytogenetic and phenotype-genotype characterisation of 3 sSCM in a 1 year-old girl exhibiting growth delay and complex cardiopathy. Design/method Array-CGH and FISH analyses were performed. Literature review was also completed in order to find a genotype-phenotype relationship in this patient. Results We found three regions of duplication, all near the centromeric region from the short chromosome arm on band q12. The first duplication was localised on chromosome 4q12 and represented a region of 5.4 Mb consisting of 326 oligonucleotides with ˜40 genes. The second duplication was on chromosome 11q12 and corresponded to a region of 1.6 Mb consisting of 84 oligonucleotides with also ˜40 genes. However, this latter duplication was much weaker and therefore probably present in mosaic. The third duplication on 12q12 was characterised by a region of 0.8 Mb with 23 oligonucleotides and included only two genes. These results were further confirmed by FISH analyses on metaphases, which revelled three distinct sSCM in this patient. The markers der (4) and der (12) were found in all cells, whereas the der (11) was absent in most cells. FISH analyses on parents revealed that these anomalies were de novo . Conclusions Remarkably, the de novo character of these three sSCM reflects the complex nature of genomic imbalances possible during embryogenesis.