Adopted son with unexplained MR

Our 10 year old adopted son has mild MR.  He also has some ear pits and a simian crease on his hand.  His MRI showed than the corpus callosum was underdeveloped (but within the range of normal).  He has an irregular and strong heart beat but once again (within the range of normal).  He has very long toes but otherwise is small (height and weights for his age - less than 5%).  He has a significant speech delay although he is able to communicate and be understood.  He has had a history of behavior problems since his adoption ranging from rages for 2-3 hours and more (when adopted - 3 years old) which have now improved to be more like aggitation/moodiness/impulsive and obsessive-compulsive (although much of the time he seems perfectly "normal" and happy).  In addition, he had significant coordination and balance issues but now plays sports (basketball and football).  He is having difficulty learning to read although he can read at about a 1st grade level.  He has never been officially diagnosed with anything other than ADHD and Mild MR.  Should we pursue having him go through genetic testing?  Any information you could provide would be appreciated.  By the way, we don't know much about his biological mother but we do know that she had very short stature (4'1") and although never tested was thought to be retarded.