What is wrong with my grand son.

Here are the facts:
He is a twin of two years of four children. They are in Germany because son-in-law is in the Army.

At birth he was the second born but larger than his twin sister.

His problem is he has limited range of motion. His muscles seem very tight as if he was a body builder. Attempting to give him stretching physical therapy hurts him.

You can see in his face the frustration of not being able to do things his four year old brother and twin sister can do.

The doctors have just gotten to the point of aggressively searching for a diagnosis. My daughter seems OK with that. She is not one for over treating and twins often are a little behind the pitch in the early years. Mental development seems fine for both twins. Maybe the one of concern is a little ahead on problem solving like puzzles. My guess is that is due to his increased focus because of his movement issues.

Please don't pull ant punches with me.

The net is frustrating because my searches just turn up political BS about every subject.

Thanks for any help.