The parents of an 18 month old boy bring their son into your office. They are concerned because while their son will take a step now and then, he really isn't "walking" and he really seems uneasy on his feet. After speaking with the parents for a little while, you learn that the patient rarely stands up from the floor but rather pushes himself up with his arms. The parents say they are also concerned because their son doesn't "babble" as much as their friend's baby and he seems to sleep more often. Upon physical examination, you notice there to be an hypertrophy of the gastrocnemius and soleus muscles bilaterally. What diagnosis would you consider for this patient and how would you confirm your diagnosis?