"De Novo" trisomy 20p with macroorchidism in a prepuberal boy.

A 9-year-old prepuberal boy with trisomy 20p syndrome and previously undescribed macroorchidism is presented. This is the second report of trisomy 20p originated "de novo" supporting a frequency rate of about the 10% for this etiological mechanism. Reviewing the most common clinical findings of all 19 previous patients, a typical phenotype with a recognizable face can be carried out in several cases. If prepuberal macroorchidism is confirmed in further patients, trisomy 20p could be taken into account in the differential diagnosis with the sex-linked syndromes with mental retardation and abnormal testicular increase.