A 4-year-old child with a small penis and small firm testes was found to have XXY/XXXY/XXXXY mosaicism. His growth and development were normal except for delayed speech. Intelligence quotient at 4 years of age was normal. Since Klinefelter's syndrome is usually not diagnosed before puberty, the finding of a small penis and small firm testes in an otherwise normal prepubescent boy should alert the physician to the possibility of this diagnosis.
Kardon NB, Beratis NG, Hsu LYF, Moloshok RE, Hirschhorn K. 47,XXY/48,XXXY/49,XXXXY Mosaicism in a 4-Year-Old Child. Am J Dis Child. 1971;122(2):160-162. doi:10.1001/archpedi.1971.02110020094014