MSRA-1049

A 3-year-old boy is brought into accident and emergency by one of the staff at the nursery that he attends. He suddenly developed facial grimacing and carpopedal spasm that morning, after a minor viral gastrointestinal infection over the past few days. On examination he also has abnormal ears, a shortened philtrum, hypertelorism, micrognathia and a heart murmur.
Which of the following is the most likely diagnosis?