copyright: Unique 2014
Approximately one boy in 1000 has XYY chromosomes. In the cells of their body, instead of 46 chromosomes including one X and one Y chromosome, they have one X and two Y chromosomes, making 47 in all. The impact of the extra Y chromosome is extremely variable. The great majority of boys and men with an extra Y chromosome are never aware of it, because they do not have symptoms that lead to a diagnosis. Only a small fraction of boys and men with XYY are ever diagnosed: recent estimates suggest 2.5% in the United Kingdom and 20% in Denmark.
- Normal appearance, typically tall stature
- Intelligence usually in the normal range, but an increased need for educational support especially with reading and writing
- Increased vulnerability to ADHD (attention deficit hyperactivity disorder)
- Increased vulnerability to autistic spectrum disorders
- Perhaps increased risk of asthma and epilepsy
Sources Recently more than 700 published studies of the outcomes of having an extra sex chromosome were identified (Leggett 2010). This guide draws chiefly on recent key studies, but also on some of the early screening studies. They are as follows: Screening studies: Walzer 1990; Götz 1999; Ratcliffe 1999 Follow-up studies of babies identified in pregnancy: Linden 2002; Lalatta 2012 Follow-up studies of babies, boys and men diagnosed because of something unusual: Schiavi 1984; Theilgaard 1984 In recent publications, babies identified in pregnancy are studied as well as boys and men identified because of a problem. These studies help to characterize the possible problems in XYY, but can give a misleading impression of how common these problems are: Geerts 2003; Ross 2009; Stochholm 2010; Bishop 2011; Bryant 2012; Cordeiro 2012; Ross 2012; Stochholm 2012; Tartaglia 2012; Bardsley 2013; Lepage 2014. The boys reported in Bishop 2011 formed a cohort for a study known as Diesc. Outcomes of this study were reported to Unique members, and are referred to here as Diesc 2010. Additional information comes from Unique families. When this guide was written, Unique had 290 XYY members. In 2003, 43 members completed a survey, and in 2014, 46 families or young men with XYY completed a survey.
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