16p12.2 microdeletion

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

16p12.2 microdeletion is a chromosomal change in which a small amount of genetic material on chromosome 16 is deleted. The deletion occurs on the short (p) arm of the chromosome at a location designated p12.2. Common characteristics that have been described in people with a 16p12.2 microdeletion include developmental delay, delayed speech, intellectual disability that ranges from mild to profound, weak muscle tone (hypotonia), slow growth resulting in short stature, an unusually small head (microcephaly), malformations of the heart, recurrent seizures (epilepsy), and psychiatric and behavioral problems.

Less common features that can occur in people with a 16p12.2 microdeletion can include hearing loss, an opening in the lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate), dental abnormalities, malformed kidneys, and genital abnormalities in males. However, there is no particular pattern of physical abnormalities that characterizes individuals with a 16p12.2 microdeletion. Signs and symptoms related to the chromosomal change vary even among affected members of the same family, and some people with the deletion have no identified physical or behavioral abnormalities.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

People with a 16p12.2 microdeletion are missing a sequence of about 520,000 DNA building blocks (base pairs), also written as 520 kb, at position p12.2 on chromosome 16. The deleted region contains seven genes and affects one of the two copies of chromosome 16 in each cell.

The signs and symptoms that can result from a 16p12.2 microdeletion are generally related to the loss of one or more genes in this region. However, it is unclear which missing genes contribute to specific features that can occur in the disorder. Because some people with a 16p12.2 microdeletion have no obvious signs or symptoms, researchers believe that other genetic or environmental factors may also be involved. In particular, studies indicate that individuals with a 16p12.2 microdeletion who have neurological or behavioral problems often have an additional, larger chromosomal deletion or duplication on another chromosome. Small duplications of genetic material that occur near the 16p12.2 microdeletion may also contribute to the features associated with this condition.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

16p12.2 microdeletion is inherited in an autosomal dominant pattern, which means one copy of the deleted region on chromosome 16 in each cell is sufficient to increase the risk of physical or developmental abnormalities.

In almost all known cases, individuals with a 16p12.2 microdeletion have inherited the chromosomal change from a parent, who may or may not have any related signs or symptoms. The condition is said to have incomplete penetrance because not everyone who has the altered chromosome develops related features.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Researchers estimate that about 1 in 2,000 newborns have a 16p12.2 microdeletion and show signs and symptoms of the condition. However, the actual number may be higher because many people with the microdeletion are likely never diagnosed. Some never come to medical attention because they have no related health or behavioral problems or have only mild signs and symptoms. Others have nonspecific features for which there can be many causes.

Which doctor should you see?

The suggested department for discussing 16p12.2 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 16p12.2 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.