The chromosomal disorder 47,XYY occurs in one in every thousand male births. Its incidence does not increase with increasing maternal age.
Clinically, individuals tend to be asymptomatic, although intelligence is typically 10-15 points below comparable siblings. 47,XYY patients also tend to be tall, although normal body proportions are otherwise maintained.
47,XYY is produced by two means. After fertilisation, there may be non-disjunction of the Y chromosome. Alternatively, a YY sperm may be produced at the second paternal meiotic division.
The recurrence rate is not increased for parents with one existing 47,XYY child.
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