Eight patients are reported with a de nov extra inverted duplicated chromosome 15. The abnormal chromosome was considered to be the same in all cases, but its precise delineation remained uncertain and was defined as either 15qter→15q12::15q12→15pter or 15pter→15q11::15q13→15pter. Analysis with various techniques of the satellite regions of the bisatellited chromosomes demonstrated maternal derivation in six and paternal derivation in one of the seven families. A nonsister chromatid exchange between the two homologous chromosomes 15 is considered a likely origin of the inv dup(15) in the cases with maternal derivation; in the only case of paternal derivation, however, the abnormal chromosome originated from one single chromosome 15. The clinical findings confirm that patients with inv dup(15) have mental and developmental retardation and are frequently affected by seizures, while severe physical malformations are absent.
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