An 8 year old boy is clinically obese. As a baby he was floppy and difficult to feed. He now has learning difficulties and is constantly eating despite measures by his parents to hide food out of reach. What is the most probable diagnosis?

The key is C. Prader Willi syndrome. [Prader Willi syndrome rare congenital disorder characterized by learning difficulties, growth abnormalities, and obsessive eating, caused especially by the absence of certain genes normally present on the copy of chromosome 15 inherited from the father].