Supernumerary marker chromosomes characterized by fluorescence in situ hybridization [FISH]

Abstract

Until recently marker chromosomes have presented a difficult diagnostic problem for cytogeneticists as well as for clinicians. Introduction of FISH to cytogenetic analysis has enabled identification of their origin giving possibility to outline specific phenotypic effects of defined marker chromosomes. Nine marker chromosomes were analysed with FISH using centromeric probes, chromosome- specific libraries and unique DNA sequences probes for PWS/AS critical region. The origin from acrocentric chromosomes was established in 6 cases. One marker was a product of maternal 11;22 translocation and two others were pericentromeric regions of chromosome 2 and 4. Among 6 markers, derived from acrocentric chromosomes, 2 consisted of pericentromeric part of chromosome 15, one was identified as mar (21) and in 3 other cases the origin could not be differentiated between chromosomes 13 and 21 or 14 and 22. Clinical consequences of marker chromosomes including the risk for chromosomal nondisjunction and trisomy 21 as well as the risk for uniparental disomy (UPD) are discussed