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Multiple mitochondrial dysfunctions syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Multiple mitochondrial dysfunctions syndrome

Multiple mitochondrial dysfunctions syndrome (MMDS) is a group of severe, early-onset disorders caused by impaired mitochondrial function, typically resulting in life-threatening metabolic complications and early childhood mortality.

Overview

Multiple mitochondrial dysfunctions syndrome (MMDS) refers to a group of severe conditions that begin early in life. These disorders affect the mitochondria, the energy-producing centers of cells. Most individuals with these conditions do not survive past early childhood.

Common Symptoms

  • Severe brain dysfunction (encephalopathy)
  • Developmental delays and loss of acquired skills (developmental regression)
  • Failure to thrive (difficulty gaining weight)
  • Lactic acidosis (buildup of lactic acid in the body)
  • Elevated levels of glycine (hyperglycinemia) or sugar (hyperglycemia) in the blood

Causes

MMDS is caused by pathogenic variants in genes responsible for creating or attaching iron-sulfur (Fe-S) clusters to proteins. These clusters are essential for various cellular processes, including energy production via oxidative phosphorylation, DNA repair, and gene regulation. When these clusters are absent, proteins cannot function, leading to reduced energy production and the severe symptoms associated with the syndrome.

Types and Genetic Associations

  • Type 1: Caused by NFU1 variants; often includes pulmonary arterial hypertension and muscle twitches.
  • Type 2: Caused by BOLA3 variants; characterized by severe encephalopathy and heart muscle weakness (cardiomyopathy).
  • Type 3: Caused by IBA57 variants; involves progressive muscle stiffness (spasticity) and paralysis.
  • Type 4: Caused by ISCA2 variants; involves spasticity and vision problems.
  • Type 5: Caused by ISCA1 variants; characterized by involuntary eye movements (nystagmus) and spasticity.

Inheritance

All types of MMDS are inherited in an autosomal recessive pattern. Both copies of the gene in each cell must have a pathogenic variant for the disorder to manifest. Parents of an affected individual are typically asymptomatic carriers.

Frequently Asked Questions

Differentiation relies heavily on specific clinical presentations and genetic testing. For example, Type 1 (NFU1) is often associated with pulmonary arterial hypertension and myoclonus, while Type 2 (BOLA3) presents with severe cardiomyopathy. Type 3 (IBA57) and Type 4 (ISCA2) are characterized by progressive spasticity, with Type 4 also involving vision problems. Since symptoms can overlap, definitive diagnosis requires identifying the specific pathogenic variant in the relevant gene through molecular genetic testing, as clinical signs alone may not be sufficient to pinpoint the exact subtype.
Currently, there is no cure for MMDS, and treatment is primarily supportive and palliative. Management focuses on addressing specific symptoms, such as using anticonvulsants for seizures, providing nutritional support for failure to thrive, and managing respiratory or cardiac complications. While research into iron-sulfur cluster biology is ongoing, no therapies have yet been proven to reverse the underlying mitochondrial dysfunction or significantly alter the disease course in clinical settings.
Newborn screening and early metabolic panels often reveal elevated levels of glycine (hyperglycinemia) or glucose (hyperglycemia) in the blood. Additionally, lactic acidosis, which indicates the body is producing excess lactic acid due to inefficient energy production, is a hallmark sign. These metabolic abnormalities can sometimes be detected shortly after birth, providing a critical window for diagnosis even if the infant appears relatively normal initially, although rapid deterioration in neurological function usually follows.
For parents who are both carriers of a pathogenic variant in the same gene, there is a 25 percent chance with each subsequent pregnancy that the child will be affected by the syndrome. There is a 50 percent chance the child will be an asymptomatic carrier, and a 25 percent chance the child will not carry the variant. Because the condition is severe and often fatal in early childhood, genetic counseling and prenatal or preimplantation genetic testing are strongly recommended for families planning additional pregnancies.
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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