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MECP2 duplication syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

MECP2 duplication syndrome

MECP2 duplication syndrome is a rare genetic condition occurring primarily in males, characterized by intellectual disability, developmental delays, and recurrent respiratory infections.

Overview

MECP2 duplication syndrome is a condition that occurs almost exclusively in males. It is characterized by moderate to severe intellectual disability. Most affected individuals experience weak muscle tone in infancy, feeding difficulties, poor or absent speech, and muscle stiffness (rigidity).

Symptoms

  • Developmental Delays: Delayed motor skills such as sitting and walking.
  • Seizures: About half of individuals experience seizures, often of the tonic-clonic type, which may not respond to medication.
  • Developmental Regression: Some individuals experience the loss of previously acquired skills.
  • Mobility: Approximately half of individuals learn to walk, while about one-third require assistance.
  • Respiratory Health: Many individuals have recurrent respiratory tract infections, which are a major cause of death.

Causes

The syndrome is caused by an extra copy of the MECP2 gene in each cell, resulting from a duplication on the long (q) arm of the X chromosome. The MECP2 gene provides instructions for making the MeCP2 protein, which is critical for normal brain function and gene regulation.

An extra copy of the gene leads to an excess of MeCP2 protein. This disrupts normal gene regulation and protein production in the brain, leading to abnormal neuronal function and the signs and symptoms of the syndrome.

Inheritance

This condition is inherited in an X-linked pattern. Because males have only one X chromosome, a duplication of the MECP2 gene is sufficient to cause the condition. In females, who have two X chromosomes, a duplication typically does not cause the disorder due to a process called X-inactivation, where one X chromosome is turned off in each cell. Females with the duplication may be unaffected or experience milder neurodevelopmental issues, such as anxiety or autism spectrum features, often due to skewed X-inactivation.

Frequently Asked Questions

Key early clues include hypotonia (floppy infant), feeding difficulties requiring tube support, poor eye contact, delayed motor milestones (e.g., sitting after 9‑12 months), and a family history of unexplained intellectual disability or early male deaths from respiratory infections. Early genetic testing (chromosomal microarray or targeted MECP2 duplication assay) is advised when these features cluster.
Preventive strategies focus on airway clearance and infection control: regular chest physiotherapy, prompt treatment of upper‑respiratory symptoms, vaccination against influenza and pneumococcus, prophylactic antibiotics during high‑risk seasons (often macrolides), and early referral to pulmonology for possible bronchoscopy or bronchodilator therapy. Maintaining optimal nutrition and avoiding exposure to sick contacts also help.
Seizures are often refractory, but many patients respond to broad‑spectrum agents such as levetiracetam, valproic acid, or clobazam. Some clinicians add a second drug (e.g., topiramate) if monotherapy fails. Because seizures can be triggered by infections or fever, aggressive fever control and early antipyretics are important adjuncts.
carrier mother has a 50 % chance of passing the duplicated X chromosome to each child. Sons who inherit the duplication will be affected; daughters who inherit it are usually asymptomatic carriers because of X‑inactivation, though rare cases of mild symptoms have been reported. Prenatal options include chorionic villus sampling or amniocentesis for targeted testing, and pre‑implantation genetic diagnosis is available for families using IVF.
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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