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3q29 microdeletion syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

3q29 microdeletion syndrome

3q29 microdeletion syndrome is a rare condition caused by the loss of a small segment of chromosome 3, leading to developmental delays and an increased risk of psychiatric disorders.

Overview

3q29 microdeletion syndrome results from the deletion of a small piece of the long (q) arm of chromosome 3 at position q29. Features vary widely; some individuals have very mild or no symptoms, while others experience significant developmental and health challenges.

Common Symptoms

  • Delayed development, particularly speech delay.
  • Mild or moderate intellectual disability.
  • Increased risk of neurodevelopmental or psychiatric disorders, including autism spectrum disorder, anxiety, bipolar disorder, and schizophrenia.
  • Feeding difficulties and failure to thrive in infancy.
  • Weak muscle tone (hypotonia).
  • Recurrent ear infections.
  • Microcephaly (unusually small head).
  • Jaundice in newborns.
  • Heart defects, most commonly patent ductus arteriosus (PDA).
  • Gastrointestinal issues, such as gastroesophageal reflux.
  • Characteristic facial features, including a long, narrow face, short philtrum, high nasal bridge, and large ears.

Frequency

The condition is very rare, with an estimated incidence of 1 in 30,000 to 40,000 people. Approximately 75 affected individuals have been described in medical literature.

Causes

Most affected individuals are missing about 1.6 million DNA base pairs at position 3q29. This region is prone to rearrangement during cell division due to short, repeated DNA sequences. The deleted segment contains approximately 20 genes, some of which are thought to be involved in brain development, though the exact relationship between specific genes and the syndrome's symptoms remains unknown.

Inheritance

This condition follows an autosomal dominant pattern of inheritance. Most cases result from a de novo (new) mutation in the affected individual with no family history. Less commonly, the deletion is inherited from a parent who may have mild or no symptoms. An extra copy of this same chromosomal segment causes a separate condition known as 3q29 microduplication syndrome.

Frequently Asked Questions

Testing is recommended if a child shows unexplained speech delay, moderate intellectual disability, recurrent ear infections, or congenital heart defects; a chromosomal microarray performed on blood or saliva can detect the ~1.6 Mb deletion.
Individuals have a markedly increased risk (up to 40 % for schizophrenia or bipolar disorder and 20–30 % for autism spectrum disorder); regular mental‑health screening by a pediatric psychiatrist or psychologist beginning in late childhood, with attention to mood changes, social withdrawal, or psychotic symptoms, is essential.
Multidisciplinary therapy—speech and language therapy, occupational therapy for hypotonia, and early childhood special education focusing on social‑communication skills—started before age three has been shown to enhance language acquisition and adaptive functioning.
Baseline cardiac evaluation (echocardiogram) to detect PDA or other defects, ophthalmologic exam for refractive errors, and periodic audiology testing for ear infections are recommended; follow‑up imaging is guided by any clinical findings.===
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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