What causes intellectual and developmental disabilities (IDDs)?

IDDs have a variety of causes. Some possible causes include (but are not limited to):^1,2,3

• Genetic mutations, additions, or deletions: for example, most cases of Rett syndrome are caused by a change in the Methly-CpG-binding Protein 2 (MECP2) gene
• Chromosome abnormalities, such as an extra chromosome or a missing chromosome: for example, Down syndrome results from having an extra copy or part of a copy of chromosome 21
• Exposure to certain substances while in the womb: for example, exposure to alcohol while in the womb can result in fetal alcohol spectrum disorder
• Infections during pregnancy: for example, infants whose mothers had cytomegalovirus during pregnancy may have hearing, vision, and neurological problems
• Problems during childbirth: for example, an umbilical cord that gets wrapped around a baby’s neck during delivery could cut off the supply of blood and oxygen to the brain resulting in IDDs
• Traumatic Brain Injury (TBI)
• Preterm birth