Our Son Has Aspergers Syndrome. He Is 12. He Also

Our son has aspergers syndrome. He is 12. He also has very low muscle tone, flexible joints, muscle weakness. He does exercises that an occupational therapist gave us. He did not walk until he was 2.5 years old. My question is: He gets purple hands & feet especially in the winter and they cold very fast (quicker than his friends) in the winter. He has really warm boots, mitts & is dressed for the weather. He also gets sharp pain around his heart area and I just discovered he gets almost not noticeable tremors in his legs and arm. I only noticed it when his legs were resting on my lap while I was trimming his nails. I asked him if he had it before. Apparently, he has these tremors on and off for some time. Could there a heart/cardio/circulatory issue? I did ask his doc about & he thought it was part in parcel of Aspergers & his heart sounded normal. My gut is to go back and blood work done.