Cytogenetic and molecular identification of a de novo direct duplication of the long arm of chromosome 4(q21.3-->q31.3).

We report on a 3-year-old boy with moderate developmental retardation, microcephaly, and malformations of ears, lids, mouth, and thumbs. Cytogenetic analysis demonstrated a direct duplication of chromosome subregion 4(q21.3-->q31.3). Confirmation of this specific rearrangement was performed by fluorescent in situ hybridization (FISH) with a chromosome painting probe and by means of quantitative Southern hybridization with DNA probes localized within the chromosome 4 region presumed to be duplicated.