Children and adults with various chromosome abnormalities may be eligible for this study, including, for example, people with developmental delay or mental retardation, abnormal growth features or growth retardation, and certain behavioral disorders. Participants will be evaluated in the clinic over a 1- to 3-day period, depending on their symptoms. All participants will be examined by a genetics specialist and will have a physical examination and possibly X-rays, computerized tomography (CT) scans, magnetic resonance imaging (MRI), ultrasound studies and medical photography. Blood will be drawn for chromosome testing-about 3 tablespoons from adults and 1 to 3 teaspoons from children.