15q13.3 microdeletion

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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.

About half of all people with a 15q13.3 microdeletion have learning difficulties or intellectual disability, which is usually mild or moderate. Many of these individuals have delayed speech and language skills. 15q13.3 microdeletion also appears to be a major risk factor for recurrent seizures (epilepsy); about one-third of people with this chromosomal change have epilepsy.

15q13.3 microdeletion has also been associated with behavioral problems, including a short attention span, aggression, impulsive behavior, and hyperactivity. Some people with a 15q13.3 microdeletion have been diagnosed with developmental disorders that affect communication and social interaction (autism spectrum disorders). This chromosomal change may also be associated with an increased risk of psychiatric disorders, particularly schizophrenia. Other signs and symptoms of 15q13.3 microdeletion can include heart defects, minor abnormalities involving the hands and arms, and subtle differences in facial features.

Some people with a 15q13.3 microdeletion do not have any of the intellectual, behavioral, or physical features described above. In these individuals, the microdeletion is often detected when they undergo genetic testing because they have an affected relative. It is unknown why a 15q13.3 microdeletion causes cognitive and behavioral problems in some individuals but few or no health problems in others.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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.

Which doctor should you see?

The suggested department for discussing 15q13.3 microdeletion is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for 15q13.3 microdeletion. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.