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MDA5 deficiency
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

MDA5 deficiency

MDA5 deficiency is a rare immune system disorder that causes severe, recurrent respiratory infections in infants due to an impaired innate immune response to certain viruses.

Overview

MDA5 deficiency is an immunodeficiency that leads to recurrent, severe infections of the lungs and airways beginning in infancy. These infections are most frequently caused by rhinovirus, though respiratory syncytial virus (RSV) and the influenza (flu) virus can also cause recurrent illness. While these viruses typically cause mild, short-lived symptoms in healthy children, individuals with MDA5 deficiency often require hospitalization. Repeated infections can contribute to chronic lung disease. As the immune system matures with age, these infections typically become less frequent.

Causes

The condition is caused by mutations in the IFIH1 gene, which provides instructions for the MDA5 protein. This protein is essential for innate immunity, the body's early, nonspecific response to pathogens.

  • Viral Recognition: The MDA5 protein recognizes double-stranded RNA, which is the genetic material of viruses like rhinovirus, RSV, and the flu.
  • Interferon Production: When MDA5 detects viral RNA, it triggers the production of interferons, which are immune system proteins that stimulate the body to fight infections.

A deficiency in MDA5 activity reduces interferon production, leaving infants without a critical early immune response and resulting in severe viral infections.

Inheritance

The inheritance pattern of MDA5 deficiency is unclear. In some cases, it appears to follow an autosomal recessive pattern, where both copies of the gene are mutated. In other instances, it appears to be autosomal dominant, where one copy of the altered gene is sufficient to cause the disorder.

Frequently Asked Questions

MDA5 is a protein that detects viral double‑stranded RNA and triggers interferon production, a key early defense. In MDA5 deficiency, this detection is impaired, so the body fails to mount a rapid antiviral response, allowing viruses like rhinovirus or RSV to replicate unchecked and cause severe disease.
Repeated severe infections can lead to chronic lung disease, such as bronchiectasis or reduced lung function. Regular pulmonary function tests and imaging (e.g., chest X‑ray or CT) every 1–2 years can help detect early changes and guide interventions.===
Early antiviral therapy (e.g., ribavirin for RSV) and supportive care are standard. Some clinicians use interferon‑beta or other immunomodulators to boost antiviral defenses, but these are still experimental and require specialist oversight.
Keep the child away from crowds during peak viral seasons, use hand sanitizers, avoid sharing utensils or drinks, and ensure that household members are vaccinated against influenza. Promptly seek medical care if the child develops fever or breathing difficulty.
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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