Proximal 18q deletion syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Proximal 18q deletion syndrome is a chromosomal condition that occurs when a piece of the long (q) arm of chromosome 18 is missing. The term "proximal" means that the missing piece occurs near the center of the chromosome. Individuals with proximal 18q deletion syndrome have a wide variety of signs and symptoms. Because only a small number of people are known to have this type of deletion, it can be difficult to determine which features should be considered characteristic of the disorder.

Most people with proximal 18q deletion syndrome have delayed development of skills such as sitting, crawling, walking, and speaking, and intellectual disability that can range from mild to severe. In particular, vocabulary and the production of speech (expressive language skills) may be delayed. Recurrent seizures (epilepsy) and weak muscle tone (hypotonia) often occur in this disorder. Affected individuals also frequently have neurodevelopmental disorders such as hyperactivity, aggression, and autism spectrum disorder that affect communication and social interaction.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Proximal 18q deletion syndrome is caused by a deletion of genetic material from one copy of chromosome 18. The deletion occurs near the middle of the q arm of the chromosome, typically in an area between regions called 18q11.2 and 18q21.2. The size of the deletion varies among affected individuals. The signs and symptoms of proximal 18q deletion syndrome are thought to be related to the loss of multiple genes from this part of chromosome 18. Researchers are working to determine how the loss of specific genes in this region contributes to the various features of this disorder.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Proximal 18q deletion syndrome is considered to be an autosomal dominant condition. This means that a deletion in one of the two copies of chromosome 18 in each cell is sufficient to cause the disorder's characteristic features.

Most cases of proximal 18q deletion syndrome are the result of a new (de novo) deletion and are not inherited from a parent. The deletion occurs most often as a random event during the formation of reproductive cells (eggs or sperm) or in early fetal development. Affected people typically have no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Deletions from the q arm of chromosome 18 occur in an estimated 1 in 55,000 newborns worldwide. However, only a small number of these individuals have deletions in the region associated with proximal 18q deletion syndrome. At least 15 people with proximal 18q deletion syndrome have been described in the medical literature.

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Intellectual disability

The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.

Hyperactivity

Hyperactivity is a condition characterized by constant and unusually high levels of activity, even in situations where it is deemed inappropriate.

Hypotonia

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Recurrent

Applies to a sign, symptom or manifestation that occurs multiple times separated by intervals in which the sign, symptom, or manifestation is not present.

Affected

This term applies to a family member who is diagnosed with the same condition as the individual who is the primary focus of investigation (the proband).

Which doctor should you see?

The suggested department for discussing Proximal 18q deletion syndrome 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 Proximal 18q deletion syndrome. 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.