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A chromosomal deletion (U.S. National Library of Medicine).
Why a person with a 15q13.3 microdeletion has symptoms, or none at all, is unknown. In this chromosomal change, a small piece of chromosome 15, on the long (q) arm at a position called q13.3, is missing in each cell. It raises the risk of intellectual disability, seizures, behavioral problems and psychiatric disorders, yet some carriers show no associated features. MedlinePlus Genetics, from the National Library of Medicine, summarizes what is known.
What it can look like
| Feature | What is known |
|---|---|
| Learning and intellectual disability | About half of people with the deletion have learning difficulties or intellectual disability, usually mild or moderate. Many have delayed speech and language |
| Seizures | A major risk factor for recurrent seizures (epilepsy); about one-third of people with the deletion have epilepsy |
| Behavior | Short attention span, aggression, impulsive behavior and hyperactivity |
| Other conditions | Some people are diagnosed with autism spectrum disorders; the deletion may raise the risk of psychiatric disorders, particularly schizophrenia |
| Physical signs | Can include heart defects, minor differences in the hands and arms, and subtle differences in facial features |
Some people have none of these features. In them the deletion is often discovered through genetic testing because a relative is affected. Why it causes cognitive and behavioral problems in some people and few or no health problems in others is unknown.
How common
The deletion likely occurs in about 1 in 40,000 people in the general population, and it appears to be more common among people with intellectual disability, epilepsy, schizophrenia or autism spectrum disorders.
The cause
Most people with the deletion lack about 2 million DNA base pairs (2 megabases) at q13.3. The size varies, but the region typically holds at least six genes. Usually one of the two copies of chromosome 15 in each cell is affected. The symptoms probably come from the loss of one or more of those genes, but it is not clear which genes explain which features. Because some carriers have no symptoms, researchers believe other genetic or environmental factors may play a part.
Inheritance
It is inherited in an autosomal dominant pattern: one copy of the deleted region is enough to raise the risk. In about 75 percent of cases the person inherits it from a parent. In the rest the parents do not carry it, and the deletion most often arises as a random event while eggs or sperm form, or in early fetal development.
Autosomal dominant inheritance (U.S. National Library of Medicine).
Autosomal dominant inheritance with a new (de novo) mutation (U.S. National Library of Medicine).
Other names are 15q13.3 microdeletion syndrome and chromosome 15q13.3 deletion syndrome.
Sources
- MedlinePlus Genetics, U.S. National Library of Medicine, "15q13.3 microdeletion," https://medlineplus.gov/genetics/condition/15q133-microdeletion/; rewritten in hubnx's own words.
Licencia: CC0 1.0 (dominio público) · Adaptado de medlineplus.gov
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