Handling small supernumerary marker chromosomes in prenatal diagnostics

Abstract

Small supernumerary marker chromosomes (sSMCs) are structurally abnormal chromosomes that cannot be thoroughly characterized by conventional banding cytogenetics and are equal in size or smaller than chromosome 20. They are present in 0.075% of prenatal cases and, overall, approximately 3 million people worldwide are carriers of a sSMC. In prenatal cases with ultrasound abnormalities, sSMCs are found in up to approximately 0.2% of the cases. First described in 1961, it is now known that sSMCs have no phenotypic effects in approximately 70% of de novo cases. Nonetheless, in at least 30–50% of prenatally detected sSMC cases, the pregnancy is terminated; that is, for a certain percentage of potentially healthy children with a sSMC, an abortion is induced. This situation can only be improved by providing increased amounts of and more reliable information on sSMCs. This article provides an overview on current state-of-the-art technologies and how sSMC analysis can be optimized in prenatal diagnostics.

Keywords::

• cytogenetics
• fluorescence in situ hybridization
• molecular cytogenetics
• prenatal diagnosis
• small supernumerary marker chromosome

Financial & competing interests disclosure

Supported in parts by the DFG (436 RUS 17/135/03; 436 RUS 17/109/04, 436 RUS 17/22/06, 436 WER 17/1/04, 436 WER 17/5/05, WE 3617/2–1, LI820/11–1, LI820/17–1), the Schering Foundation, the Boehringer Ingelheim Fonds, the University Jena “Pro Chance 2008” and the Evangelische Studienwerk e.V. Villigst. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.