Turner syndrome is caused by complete or partial absence of the 2^nd X chromosome and affects about 1/2500 females. To localize the region of the X chromosome responsible for congenital heart defects (CHD) in the syndrome, this study compared the prevalence of CHD in groups missing the entire 2^nd X to those missing only the X chromosome short arm(Xp) or long arm(Xq). They showed that CHD are found in ~30% of girls missing the entire 2^nd X and in 27% of those missing only the X short arm, but in none of those missing only the X long arm, proving that a gene involved in cardiac development is located on the X chromosome short arm. (By Dr Carolyn Bondy, http://jmg.bmj.com/content/early/2013/07/02/jmedgenet-2013-101720 )