A correction for this article has been published in Molecular Cytogenetics 2009, 2:8

Case report

Characterization of a prenatally assessed de novo supernumerary minute ring chromosome 20 in a phenotypically normal male

Sofia Kitsiou-Tzeli¹ , Emmanouil Manolakos² , Magdalini Lagou² , Maria Kontodiou² , Nadezda Kosyakova³ , Elisabeth Ewers³ , Anja Weise³ , Antonios Garas⁴ , Sandro Orru⁵ , Thomas Liehr³ and Aikaterini Metaxotou²

¹  Department of Medical Genetics, University of Athens, Aghia Sofia Children's Hospital, GR-11527, Athens, Greece

²  Bioiatriki S.A, Kifisias Av. 132 and Papada, GR-115 26 Athens, Greece

³  Institute of Human Genetics and Anthropology, Kollegiengasse 10, D-07743 Jena, Germany

⁴  Department of Obstetrics and Gynecology, University of Thessaly, Larissa, Greece

⁵  Department of Medical Genetics, University of Cagliari, Binaghi Hospital, Cagliari, Italy

author email corresponding author email

Molecular Cytogenetics 2009, 2:1doi:10.1186/1755-8166-2-1

Published:	7 January 2009

Abstract

Background

The heterogeneous group of small supernumerary marker chromosomes (sSMCs) presents serious counseling problems, especially if they are present de novo and diagnosed prenatally. The incidence has been estimated at 1 in 1000 prenatal samples. We present a case of mosaic sSMC diagnosed prenatally after amniocentesis. The sSMC was characterized by various molecular cytogenetic techniques and determined to be a r(20) chromosome. After genetic counseling, the parents decided to continue the pregnancy, and a boy with minor phenotypic variants was born after 39 weeks of pregnancy. The case is compared with four other cases of prenatally detected r(20) mosaicism.

Results

Here we describe a 3 months old male child with normal pre- and postnatal development and with a de novo ring supernumerary marker chromosome in amniocytes cultures. Using new fluorescence in situ hybridization (FISH) techniques, three distinguishable sSMCs (cryptic mosaicism), all derived from chromosome 20, were observed, including ring and minute chromosomes. This heterogeneity was impossible to detect by the conventional G-banding technique or conventional FISH technique that were used before the application of new FISH techniques (subcentromere-specific multicolor-FISH [subcenM-FISH]) and a probe, specific for the 20p12.2 band. The sSMC present in 25% of the cells was present as r(20)(::p12.2~12.3->q11.1::)[5]/r(20;20)(::p12.1->q11.1::q11.1 >p12.1::)[2]/min(20;20)(:p12.1->q11.1::q11.1->p12.1:)[1]. The final karyotype was 47,XY,+r(20)[25%]/46,XY[75%].

Conclusion

We emphasize the importance of application of molecular cytogenetics in a prenatally diagnostic laboratory and description of more cases to enable a better genetic counseling and risk evaluation.