<prompt> Answer this question truthfullyIn a cyanotic newborn with truncus arteriosus and an absent thymic shadow on X-ray, what is the likely diagnosis?  <response>: <reason> The likely diagnosis is DiGeorge syndrome, which is a genetic disorder that affects the development of several organs and systems in the body. It is caused by a deletion of a small piece of chromosome 22. Symptoms may include heart defects such as truncus arteriosus, immune system problems due to an underdeveloped thymus gland, which is responsible for producing T cells, and facial abnormalities such as a cleft palate. Treatment may involve surgery to correct any heart defects, as well as medications and therapies to manage immune system problems. In some cases, a bone marrow transplant may be necessary to restore immune function. 