MECP2 duplication syndrome is an inherited disorder that occurs almost exclusively in males. Symptoms of this syndrome include moderate to severe intellectual disability, weak muscle tone, feeding difficulties, poor or absent speech, seizures, muscle stiffness, and recurrent respiratory tract infections. Children with MECP2 duplication syndrome have slow development of motor skills such as sitting and walking, or loss of previously acquired skills. About half of affected males die before the age of 25 years, mostly from complications of recurrent respiratory infections and/or neurologic deterioration. There is no specific treatment available but medical surveillance and care may help to improve some symptoms and overall condition of life. MECP2 duplication syndrome is caused by the duplication of genetic material on a specific region on the X chromosome that includes a gene named MECP2.