The parents of a 17-year-old boy with Down syndrome seek counseling because they are concerned that their son may develop a life-threatening disorder known to be associated with his chromosomal abnormality. The physician should be prepared to discuss which of the following disorders in terms of its association with Down syndrome?

Patients with Down syndrome are at increased risk of lymphoblastic leukemia. In addition, there is common occurrence of congenital hea disease, especially defects of the endocardial cushion (atrioventricular valve malformations and atrial and ventricular septal defects), and increased susceptibility to infection. Many patients with Down syndrome who are > 35 years of age show signs, symptoms of Alzheimer-type dementia