An extremely rare condition in males in which they have two Y chromosomes instead of one. They grow faster than normal, and their final height is approximately 7cm above average. Many experience severe acne during adolescence.
XYY syndrome is a tail-stature syndrome in males with an extra Y chromosome and is characterized by behavioral disorders that manifest in puberty. The main distinguishing characteristics of the syndrome are that the boys have tall stature (> 180 cm), behavior disorders in over 50% of cases, and delayed speech. This syndrome may be differentially diagnosed with Marfan syndrome, and there are no masculine or feminine characteristics specifically associated with this genotype.