This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
A 5-year-old boy with normal motor skills has severe language delay, shows no interest in interacting with other children or with adults, and spends a lot of time spinning around. The most likely diagnosis for this child is 
Select and explain. 
A. Attention deficit hyperactivity disorder (ADHD), B. Rett syndrome, C. Conduct disorder, D. Infantile autism
D: Infantile autism
Answer: D: Infantile autism 
Explanation: The most likely diagnosis for this 5-year-old boy with normal motor skills, severe language delay, and stereo typical spinning movements who shows no interest in interacting with others is infantile autism, a pervasive developmental disorder of childhood. In contrast, children with attention deficit hyperactivity disorder (ADHD) show problems paying attention or with excessive activity but not language delay. Children with conduct disorder show behaviors like stealing, truancy, and setting fires. Mentally retarded children may have language delay but interact with others in a relatively normal fashion. Rett syndrome, which involves some behavioral features of infantile autism such as stereotypical movements, is seen only in girls.