If your son is receiving adequate relacement meds, he will be fine. Just make sure to keep up with regular bloodwork to monitor his levels and have the doctor adjust accordingly.
Hooray for the PKU test that caught it!
Thank you for your comment. When my pediatrician contacted us about the results of my baby's PKU he said it was critical that I have him at the doctor ASAP. He was born on a Monday, PKU was done on Tuesday and the doctor called us on Thursday and said I had to have him at an endocrinoligists on Monday. He said that the thyroid stimulates the pituitary gland which in turn causes the brain to develop in babies. He said in babies it is vital that they begin to receive synthetic hormone ASAP because their brain development depends on it. He used terms like cretism which is eventual deformity of the face, lack of growth, and severe retardation if left untreated. I was told that if a baby can begin receiving the synthetic hormone within a week of birth there is a great chance no brain damage has occurred, but any later than that the risk increases. At the hospital after my baby's birth I was amazed at how quiet he was and how he wouldn't wake to eat for 6 hours or more. Little did I know at the time what was actually causing it. He is healthy and happy now, but he will take medication for the rest of his life. My question or my concern was on rather I should be worried about his future development or health matters related to his thyroid.
You might be more interested in finding out about the human growth hormone. I don't believe the thyroid controls the growth factor. You might search the net for HGH instead. There might also be someone here that knows something about this, so keep checking the forum.