3p deletion syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

3p deletion syndrome is a condition that results from a chromosomal change in which a small piece of chromosome 3 is deleted in each cell. The deletion occurs at the end of the short (p) arm of the chromosome. This chromosomal change often leads to intellectual disability, developmental delay, and abnormal physical features.

Individuals with 3p deletion syndrome typically have severe to profound intellectual disability. Most have delayed development of language skills as well as motor skills such as crawling and walking. While affected individuals learn to walk in childhood, their language ability usually remains limited. Some individuals with 3p deletion syndrome have obsessive-compulsive disorder (OCD) or features of autism spectrum disorders, which are conditions characterized by impaired communication and social interaction.

The physical signs and symptoms of 3p deletion syndrome vary greatly. Many affected individuals have slow growth, an abnormally small head (microcephaly), a small jaw (micrognathia), droopy eyelids (ptosis), malformed ears or nose, and widely spaced eyes (hypertelorism). Other frequent features include skin folds covering the inner corner of the eyes (epicanthal folds), extra fingers or toes (polydactyly), and an opening in the roof of the mouth (cleft palate). Additionally, individuals with 3p deletion syndrome may have seizures, weak muscle tone (hypotonia), intestinal abnormalities, or congenital heart defects.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

3p deletion syndrome is caused by deletion of the end of the small (p) arm of chromosome 3. The size of the deletion varies among affected individuals, ranging from approximately 150,000 DNA building blocks (150 kilobases or 150 kb) to 11 million DNA building blocks (11 megabases or 11 Mb). The deletion can include between 4 and 71 known genes. In some individuals, the deletion involves material near the end of the chromosome but does not include the tip (the telomere).

The signs and symptoms related to 3p deletion syndrome result from the loss of genes in the 3p region. It is difficult to determine which genes may be responsible for which specific features of 3p deletion syndrome because of the variability in both the size of the deletion and in the signs and symptoms of the condition among affected individuals. Multiple genes at the end of chromosome 3 appear to play a role in neurological development, but because not all people with 3p deletion syndrome are missing the same genes, it is difficult to pinpoint which ones influence the cognitive symptoms. It is likely that the loss of multiple genes contribute to the different physical abnormalities.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Most cases of 3p deletion syndrome are not inherited. The deletion occurs in one chromosome, most often as a random event during the formation of reproductive cells (eggs or sperm) or in early fetal development. In these cases, affected people have no history of the disorder in their family.

In rare cases, 3p deletion syndrome is inherited, usually from a mildly affected parent. The deletion can also be inherited from an unaffected parent who carries a chromosomal rearrangement between chromosome 3 and another chromosome. This rearrangement is called a balanced translocation. No genetic material is gained or lost in a balanced translocation, so these chromosomal changes usually do not cause any health problems. However, translocations can become unbalanced as they are passed to the next generation. Children who inherit an unbalanced translocation have a chromosomal rearrangement with extra or missing genetic material. Individuals with 3p deletion syndrome associated with an unbalanced translocation are missing genetic material from the short arm of chromosome 3, which results in the signs and symptoms of this disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

3p deletion syndrome is likely a rare disorder; at least 30 cases have been described in the scientific literature.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Cognitive impairment · Very frequent (99-80%)

Abnormal cognition is characterized by deficits in thinking, reasoning, or remembering.

Hypertelorism · Very frequent (99-80%)

Interpupillary distance more than 2 SD above the mean (alternatively, the appearance of an increased interpupillary distance or widely spaced eyes).

Long philtrum · Very frequent (99-80%)

Distance between nasal base and midline upper lip vermilion border more than 2 SD above the mean. Alternatively, an apparently increased distance between nasal base and midline upper lip vermilion border.

Micrognathia · Very frequent (99-80%)

Developmental hypoplasia of the mandible.

Ptosis · Very frequent (99-80%)

The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective).

Short stature · Very frequent (99-80%)

A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms).

Telecanthus · Very frequent (99-80%)

Distance between the inner canthi more than two standard deviations above the mean (objective); or, apparently increased distance between the inner canthi.

Atrioventricular canal defect · Frequent (79-30%)

A defect of the atrioventricular septum of the heart.

Other findings in the same source

From: Orphanet

Additional reported features include Brachycephaly (Frequent (79-30%)); Cleft palate (Frequent (79-30%)); Cryptorchidism (Frequent (79-30%)); Downturned corners of mouth (Frequent (79-30%)); Epicanthus (Frequent (79-30%)); Hearing impairment (Frequent (79-30%)); High palate (Frequent (79-30%)); Hypotonia (Frequent (79-30%)); Intrauterine growth retardation (Frequent (79-30%)); Microcephaly (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing 3p 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 3p 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.