SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) is a rare disorder of bone growth characterized by skeletal, brain, and skin abnormalities.~All people with this condition have extremely short stature with particularly short arms and legs. Other features include unusual bowing of the leg bones; a small chest with short ribs and curved collar bones; short, broad fingers; and folds of extra skin on the arms and legs. Structural abnormalities of the brain cause seizures, profound developmental delay, and intellectual disability. Several affected individuals also have had episodes in which their breathing slows or stops for short periods (apnea). Acanthosis nigricans, a progressive skin disorder characterized by thick, dark, velvety skin, is another characteristic feature of SADDAN that develops in infancy or early childhood.