Hi...my Nephew Is A Healthy 1.5 Yrs Boy Child.and He

Hi...my nephew is a healthy 1.5 yrs boy child.and he suffers from involuntary body jerks while he was in sleep.it was so severeve that he could able to speak any words too.ouw family members did hav this type of problm earlier and the child is a healty one too..but suddenly what happen to him.plz help