Abstract
A nine-year-old male with developmental abnormalities was found to be mosaic for an extra No. 9 chromosome (46,XY/47,XY,+9). The clinical findings included severe mental retardation, peculiar facies, short stature, hypotonia, dextroposition with a ventricular septal defect, and patent ductus arteriosus, as well as significant abnormalities of the brain.