15q13.3 microdeletion is a chromosomal change in which a small piece of chromosome 15 is deleted in each cell. The deletion occurs on the long (q) arm of the chromosome at a position designated q13.3. This chromosomal change increases the risk of intellectual disability, seizures, behavioral problems, and psychiatric disorders. However, some people with a 15q13.3 microdeletion do not appear to have any associated features.
15q13.3 microdeletion likely occurs in about 1 in 40,000 people in the general population. It appears to be more common in people with intellectual disability, epilepsy, schizophrenia, or autism spectrum disorders.
Most people with a 15q13.3 microdeletion are missing a sequence of about 2 million DNA building blocks (base pairs), also written as 2 megabases (Mb), at position q13.3 on chromosome 15. The exact size of the deleted region varies, but it typically contains at least six genes. This deletion usually affects one of the two copies of chromosome 15 in each cell.
The signs and symptoms that can result from a 15q13.3 microdeletion are probably related to the loss of one or more genes in this region. However, it is unclear which missing genes contribute to the specific features of the disorder. Because some people with a 15q13.3 microdeletion have no obvious signs or symptoms, researchers believe that other genetic or environmental factors may also be involved.
15q13.3 microdeletion is inherited in an autosomal dominant pattern, which means one copy of the deleted region on chromosome 15 in each cell is sufficient to increase the risk of intellectual disability and other characteristic features.
In about 75 percent of cases, individuals with 15q13.3 microdeletion inherit the chromosomal change from a parent. In the remaining cases, 15q13.3 microdeletion occurs in people whose parents do not carry the chromosomal change. In these individuals, the deletion occurs most often as a random event during the formation of reproductive cells (eggs and sperm) or in early fetal development.
This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/condition/15q133-microdeletion