XYY syndrome

The XYY syndrome occurs in about 1 per 1000 liveborn male
infants, due to nondisjunction at paternal meiosis II. Fetal loss
rate is very low. The majority of males with this karyotype have
no evidence of clinical abnormality and remain undiagnosed.
Accelerated growth in early childhood is common, leading to
tall stature, but there are no other physical manifestations of
the condition apart from the occasional reports of severe acne.
Intelligence is usually within the normal range but may be
about 10 points lower than in siblings and learning difficulties
may require additional input at school. Behavioural problems
can include hyperactivity, distractability and impulsiveness.
Although initially found to be more prevalent among inmates
of high security institutions, the syndrome is much less strongly
associated with aggressive behaviour than previously thought
although there is an increase in the risk of social
maladjustment.