15q11.2 microdeletion refers to a chromosome abnormality in which a tiny piece of genetic material on the long arm of chromosome 15 (at a location designated q11.2) is missing (deleted). The features of people with a 15q11.2 microdeletion vary widely. The most common features include developmental, motor, and language delays; behavior and emotional problems; attention deficit disorders; and autism spectrum disorder. Other features may include birth defects and seizures. However, some people have no apparent physical, learning, or behavior problems. A 15q11.2 microdeletion may occur randomly for the first time in an affected person, or it may be inherited from a parent. Treatment depends on the signs and symptoms in each person.

The signs and symptoms in people with a 15q11.2 microdeletion can vary widely. Some people with the microdeletion don't have any apparent features, while others are more severely affected. When not all people with a genetic abnormality are affected, the condition is said to have reduced penetrance. When signs and symptoms vary among affected people, the condition is said to have variable expressivity.

The most commonly reported features in people with a 15q11.2 microdeletion include:

• Neurological dysfunction
• Developmental delay
• Language delay
• Motor delay
• ADD/ADHD
• Autism spectrum disorder.

Other signs and symptoms that have been reported include seizures; abnormally shaped ears; abnormalities of the palate (roof of the mouth); memory problems; behavioral problems; and mental illness. While some babies with a 15q11.2 microdeletion are born with a minor or serious birth defect, many babies are born completely healthy.