Partial trisomy for short arm of chromosome 5.

We present two unrelated cases of partial trisomy for the short arm of chromosome 5, the first such cases reported in Japan. The features are characterized by hypertelorism, low set ears, arachnodactyly, laryngostenosis, hypotonia and some cerebral malformation. The characteristic facial expression and arachnodactyly are the key features used to diagnose this disorder. A high-resolution chromosome banding technique showed that the karyotype of the first patient was 46,XX,inv dup(5) (p13.1-->p15.3) de novo and that of the second patient was 46,XX,dir dup(5) (p13.3-->p15.2) de novo. The similar symptoms in the two cases, despite the difference in karyotypes, were caused by duplication of 5p including segment 5p13. This would be a key site for this disorder.