Duplication 20p identified via fluorescent in situ hybridization.

A 3-year-old girl is reported with dup (20p) resulting from 3:1 segregation of a de novo t(20;21). The proposita presented with minor anomalies, developmental delay, a clinical phenotype suggestive of 20p trisomy, and a karyotype with a 21p+ and an additional small marker chromosome. Conventional cytogenetic techniques were not informative for the identification of the origin of the extra material of chromosome 21p nor for the marker chromosome. The 21p+ and marker chromosomes were successfully characterized using fluorescent in situ hybridization (FISH).