3q29 microdeletion syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

3q29 microdeletion syndrome (also known as 3q29 deletion syndrome) is a condition that results from the deletion of a small piece of chromosome 3 in each cell. The deletion occurs on the long (q) arm of the chromosome at a position designated q29.

The features associated with 3q29 microdeletion syndrome vary widely. Some individuals with this chromosomal change have very mild or no related signs and symptoms, and the deletion is discovered through genetic testing only after a family member is diagnosed. However, most people with a 3q29 microdeletion have delayed development (particularly speech delay) and mild or moderate intellectual disability. They also have an increased risk of neurodevelopmental or psychiatric disorders, including autism spectrum disorder (which affects social interaction and communication), anxiety, bipolar disorder, and schizophrenia.

Infants with 3q29 microdeletion syndrome often have feeding difficulties and do not grow and gain weight at the expected rate (faltering weight). Weak muscle tone (hypotonia), recurrent ear infections, an unusually small head (microcephaly), and yellowing of the skin and whites of the eyes (jaundice) can also occur. Some affected babies are born with a heart defect, most commonly an abnormal connection between two major arteries called patent ductus arteriosus (PDA).

Other possible features of 3q29 microdeletion syndrome include gastrointestinal disorders, such as a backflow of acidic stomach contents into the esophagus (gastroesophageal reflux), and abnormalities of the teeth. There may also be a subtle pattern of characteristic facial features, including a long, narrow face; a narrow space between the nose and upper lip (short philtrum); a high bridge of the nose; and large ears.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Most people with 3q29 microdeletion syndrome are missing about 1.6 million DNA building blocks (base pairs), also written as 1.6 megabases (Mb), at position q29 on chromosome 3. This deletion affects one of the two copies of chromosome 3 in each cell.

The segment that gets deleted is surrounded by short, repeated sequences of DNA that make it prone to rearrangement during cell division. The rearrangement can lead to missing or extra copies of DNA at 3q29. (An extra copy of this segment causes another condition called 3q29 microduplication syndrome.)

The chromosome segment most commonly deleted in people with 3q29 microdeletion syndrome contains about 20 genes. Some of these genes are thought to be involved in brain development. However, it is unknown which specific genes, when deleted, are related to the signs and symptoms of 3q29 microdeletion syndrome. It is also unclear why some people with a deletion at 3q29 have no associated health problems. It is possible that genetic changes outside the 3q29 region can influence the features of this condition.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition has an autosomal dominant pattern of inheritance, which means the deletion occurs on one copy of chromosome 3 in each cell.

Most cases of 3q29 microdeletion syndrome result from a new (de novo) chromosomal change and occur in people with no history of the deletion in their family. Less commonly, an affected person inherits the deletion from a parent. The parent may have no signs and symptoms related to the deletion, or the features may be mild.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

3q29 microdeletion syndrome appears to be very rare. Based on a study from Iceland, the condition has an estimated incidence of 1 in 30,000 to 40,000 people in that population. About 75 affected individuals have been described in the medical 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.

Global developmental delay · Very frequent (99-80%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Intellectual disability · Very frequent (99-80%)

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.

Delayed speech and language development · Frequent (79-30%)

A degree of language development that is significantly below the norm for a child of a specified age.

Everted lower lip vermilion · Frequent (79-30%)

An abnormal configuration of the lower lip such that it is turned outward i.e., everted, with the Inner aspect of the lower lip vermilion (normally opposing the teeth) being visible in a frontal view.

Low-set ears · Frequent (79-30%)

Upper insertion of the ear to the scalp below an imaginary horizontal line drawn between the inner canthi of the eye and extending posteriorly to the ear.

Macrotia · Frequent (79-30%)

Median longitudinal ear length greater than two standard deviations above the mean and median ear width greater than two standard deviations above the mean (objective); or, apparent increase in length and width of the pinna (subjective).

Microcephaly · Frequent (79-30%)

Head circumference below 2 standard deviations below the mean for age and gender.

Prominent nasal bridge · Frequent (79-30%)

Anterior positioning of the nasal root in comparison to the usual positioning for age.

Other findings in the same source

From: Orphanet

Additional reported features include Short philtrum (Frequent (79-30%)); Abnormality of skin pigmentation (Occasional (29-5%)); Abnormality of the dentition (Occasional (29-5%)); Aggressive behavior (Occasional (29-5%)); Anxiety (Occasional (29-5%)); Attention deficit hyperactivity disorder (Occasional (29-5%)); Autism (Occasional (29-5%)); Bipolar affective disorder (Occasional (29-5%)); Cataract (Occasional (29-5%)); Clinodactyly of the 5th finger (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing 3q29 microdeletion 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 3q29 microdeletion 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.