Klinefelter (47XXY)

• Frequency 1 in 1000, but presentation is later
• 10% mosaic
• XXXy and XXyy males are similar but with greater mental retardation

Characteristics

• Mental retardation
• intention tremor
• behavioral problems
• tall stature
• hypogonadism; small firm testes; usually sterile; penis may be normal in size; often begin puberty at normal age, but do not progress normally (in ddx of delayed puberty)
• gynecomastia in 50% (occasional breast cancer)
• Adults have female distribution of body fat
• facial hair is sparse and body hair scanty

Recurrence risk is 1-2% but does increase with advanced maternal age

CHLA board review course 2005
Baraitser and Winter, 1996. Color Atlas of Congenital Malformation Syndromes