Brief report: a case study of an adolescent male with XXXXY Klinefelter's syndrome.

The developmental history of a 14-year-old male with Klinefelter's syndrome (XXXXY) is described. A review of the XXXXY literature focuses on the physical complications and the mental deficiency associated with this syndrome. This case study describes an individual whose physical development is consistent with many patterns described in the XXXXY literature, although his retardation is not as severe as generally described. His personality and learning style are more similar to descriptions of XXY Klinefelter individuals. A detailed analysis of more XXXXY cases is essential to clarify developmental patterns and learning capacity in individuals with XXXXY syndrome. Severe retardation may no longer need to be the anticipated developmental outcome.