Q. A 2-year-old boy is brought to the clinic by his parents. They are concerned about their son's development, noting he has not been reaching typical developmental milestones. In addition, they report he has been experiencing recurrent seizures. During the physical examination, the physician notices that the child has a small head , hypopigmented skin, and a rash consistent with eczema. Moreover, a distinctive musty body odor is detectable. Based on these findings, which of the following is the most likely diagnosis?