An incomplete trisomy 3 rescue resulting in a marker chromosome and UPD(3)—difficulties in interpretation

Abstract

Trisomy 3 and marker chromosomes derived from chromosome 3 are rare cytogenetic findings. Confined placental mosaicism (CPM) of trisomy 3 was reported and in such cases, intrauterine growth retardation (IUGR) and intrauterine fetal death (IUFD) were occasionally seen. A case of trisomy 3 mosaicism in amniotic fluid was once detected in a newborn with a normal phenotype at birth and symmetric IUGR, probably resulting from the placental trisomic cell lines (Zaslav et al., 2004). There are only four cases of mosaic trisomy 3 in liveborn infants (confirmed in blood lymphocytes) with all showing an abnormal phenotype (Schinzel, 2001). There are several (19) published reports of chromosome-3-derived marker chromosomes (patients with complex karyotype, unpublished cases and tumor cell lines were excluded; http://www.med.uni-jena.de/fish/ sSMC/03.htm#unclear). Nine cases showed a normal phenotype; however, three of them were prenatal cases not evaluated after birth. An abnormal phenotype was reported in ten cases. We present the first documented case of an ‘incomplete’ trisomy 3 rescue, which resulted in an extra chromosome-3-derived marker chromosome in the fetus. Fluorescent in situ hybridization (FISH) and DNA studies were performed in order to characterize the marker chromosome and to elucidate the mechanism of formation, respectively. In order to assess a genotype–phenotype correlation, we compared our case with similar cases in the literature.