Not sure what you mean exactly when you say your son's leg "spasms." I'm assuming that you mean the myoclonic jerking of the leg. Unfortunately, segmental or spinal myoclonus is one of the few movement disorders to persist in sleep. Not only that, but it is known to persist indefinitely throughout life. Glad all of the tests were okay as this can be caused by things like tumor and trauma or mistaken for seizures. Medications that have been successful for patients in the past include tetrabenezine, tegretol, and of course klonopin which is the first line drug. If all of this has been tried and his life is greatly affected by it, then consider a second opinion at a movement disorders center at a major clinical/academic hospital. Columbia Presbyterian in NY is one of the world's best. Good luck.