The first case of a small supernumerary marker chromosome derived from chromosome 10 in an adult woman with an apparently normal phenotype

Small supernumerary marker chromosomes (sSMCs) originating from chromosome 10 are rare. A limited number of cases are documented. We report a new diagnosis of a mosaic sSMC (10) in a normal female who asked for genetic evaluation before undergoing controlled ovarian hyperstimulation, in vitro fertilization, and embryo transfer. Chromosome preparations from peripheral lymphocyte cultures were performed according to standard procedures. QFQ-banded chromosomes confirmed the presence of an sSMC: 47,XX,+mar[49]/46,XX[51]. FISH and array CGH analysis showed that the sSMC consisted of chromosome 10 with a gain of the 10p11.1p11.21 (2.5 Mb) chromosomal region. The presence of sSMC (10) was also confirmed in the patient's mother and sister. It did not appear to affect the phenotype of the women who were phenotypically normal and healthy, and at the time of writing the woman became pregnant naturally. Phenotypes associated with an sSMC vary from normal to severely abnormal. It has been shown that variations in the chromosomal region of sSMCs result in observable differences in clinical outcome. The phenotypical consequences of sSMCs are difficult to predict because of differences in euchromatic DNA content, chromosomal origin, and varying degrees of mosaicism. Therefore, the continued investigation of a larger number of sSMC cases, in particular those originating from chromosome 10 that are the infrequently encountered and characterized, and a better understanding of the genetic content is important in order to improve the delineation of karyotype-phenotype correlation, contributing to a more informed prenatal counseling or prognosis.