triple X syndrome

The triple X syndrome occurs with an incidence of 1 in 1200
liveborn female infants and is often a coincidental finding. The
additional chromosome usually arises by a nondisjunction error
in maternal meiosis I. Apart from being taller than average,
affected girls are physically normal. Educational problems are
encountered more often in this group than in the other types
of sex chromosome abnormalities. Mild delay with early motor
and language development is fairly common and deficits in
both receptive and expressive language persist into adolescence
and adulthood.