MDA5 deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

MDA5 deficiency is a disorder of the immune system (immunodeficiency) that leads to recurrent, severe infections of the lungs and airways (respiratory tract) beginning in infancy. These infections are most frequently caused by rhinovirus (the virus that causes the common cold). Respiratory syncytial virus (RSV) and the influenza (flu) virus may also cause recurrent infections in affected individuals. While infection by these viruses is common in all children, it usually causes mild symptoms and lasts only a short time before being cleared by a healthy immune system. In contrast, individuals with MDA5 deficiency frequently require hospitalization due to the severity of the symptoms caused by the infection. Repeated infections can contribute to chronic lung disease.

Infections usually become less frequent with age in people with MDA5 deficiency, as the body's immune system matures and develops other mechanisms for fighting viruses.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

MDA5 deficiency is caused by mutations in the IFIH1 gene, which provides instructions for making the MDA5 protein. These mutations lead to production of an altered MDA5 protein that cannot function, resulting in a shortage (deficiency) of MDA5 activity.

The MDA5 protein plays an important role in innate immunity, the body's early, nonspecific response to foreign invaders (pathogens) such as viruses and bacteria. In particular, the protein recognizes a molecule called double-stranded RNA (a chemical cousin of DNA), which certain viruses, including rhinovirus, RSV, and the flu virus, have as their genetic material or produce when they infect cells and copy (replicate) themselves. (Another subset of viruses has DNA as their genetic material.) When the MDA5 protein recognizes pieces of viral RNA inside the cell, it helps turn on the production of immune system proteins called interferons. Interferons stimulate the immune system to fight infections.

Deficiency of MDA5 protein activity reduces interferon production in response to RNA-containing viruses. A lack of the important early immune response stimulated by interferons leads to severe viral infections in infants with MDA5 deficiency.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

The inheritance pattern of MDA5 deficiency is unclear. In some cases, the condition seems to follow an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. In other cases, it appears that the condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

MDA5 deficiency is likely a rare disorder. Its prevalence is unknown.

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Chronic lung disease

According to the definitions of the American and British Thoracic Societies, including pulmonary functional tests, X-rays, and CT scans for items such as fibrosis, bronchiectasis, bullae, emphysema, nodular or lymphomatous abnormalities.

Immunodeficiency

Failure of the immune system to protect the body adequately from infection, due to the absence or insufficiency of some component process or substance.

Recurrent

Applies to a sign, symptom or manifestation that occurs multiple times separated by intervals in which the sign, symptom, or manifestation is not present.

Affected

This term applies to a family member who is diagnosed with the same condition as the individual who is the primary focus of investigation (the proband).

Healthy

No history of any serious disease, including the disease being investigated in the proband.

Which doctor should you see?

The suggested department for discussing MDA5 deficiency 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 MDA5 deficiency. 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.