Down syndrome.

Down syndrome (DS; Trisomy 21) is the most common chromosomal disorder in humans. It has numerous associated neurologic phenotypes including intellectual disability, sleep apnea, seizures, behavioral problems, and dementia. With improved access to medical care, people with DS are living longer than ever before. As more individuals with DS reach old age, the necessity for further life span research is essential and cannot be overstated. There is currently a scarcity of information on common medical conditions encountered as individuals with DS progress into adulthood and old age. Conflicting information and uncertainty about the relative risk of dementia for adults with DS is a source of distress for the DS community that creates a major obstacle to proper evaluation and treatment. In this chapter, we discuss the salient neurologic phenotypes of DS, including Alzheimer's disease (AD), and current understanding of their biologic bases and management.