Can ya help me with this Step 1 question?

A 5-year-old boy is brought to the physician by his parents because of an 8-month history of difficulty walking. His parents say that he limps when he walks and has a waddling gait; he also has difficulty standing. When getting up from a sitting position, he uses his hands to walk up his thighs and push his body into a standing position. His mother is an only child but she has an uncle who became bedridden as a child and died of respiratory arrest. Physical examination of the boy shows... Can ya help me with this Step 1 question?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums