Hello, my son, 18 months was dx in utero with xyy syndrome. His cord was a marginl insertion, so he was tiny at almost full term. He has not made it on the growth charts yet...even with extra calories and feedings. He is -5 in weights and 3 percent in height. We had blood work done, both 1 and 2 growth hormones were low. Not in the range. We have an enodo appt on tuesday. How will this be affected by the xyy?... Usually very tall boys