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Autosomal recessive congenital methemoglobinemia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Autosomal recessive congenital methemoglobinemia

Autosomal recessive congenital methemoglobinemia is an inherited blood disorder that alters hemoglobin, leading to oxygen deprivation and a characteristic bluish skin appearance.

Overview & Types

Autosomal recessive congenital methemoglobinemia is an inherited condition that mainly affects the function of red blood cells. Specifically, it alters a molecule within these cells called hemoglobin. Hemoglobin carries oxygen to cells and tissues throughout the body. In people with autosomal recessive congenital methemoglobinemia, some of the normal hemoglobin is replaced by an abnormal form called methemoglobin, which is unable to deliver oxygen to the body's tissues. As a result, tissues in the body become oxygen deprived, leading to a bluish appearance of the skin, lips, and nails (cyanosis).

There are two forms of autosomal recessive congenital methemoglobinemia:

  • Type I: People with type I have cyanosis from birth and may experience weakness or shortness of breath related to the shortage of oxygen in their tissues. People with type I have a normal life expectancy.
  • Type II: People with type II have cyanosis as well as severe neurological problems. After a few months of apparently normal development, children with type II develop severe brain dysfunction (encephalopathy), uncontrolled muscle tensing (dystonia), and involuntary limb movements (choreoathetosis). Additionally, the size of their head remains small and does not grow in proportion with their body. People with type II have severe intellectual disability; they can recognize faces and usually babble but speak no words. They can sit unassisted and grip objects but have impaired motor skills that leave them unable to walk. Growth is often slowed, and abnormal facial muscle movements can interfere with swallowing, which can lead to feeding difficulties and further slow growth. People with type II often do not survive past early adulthood.

Frequency

The incidence of autosomal recessive congenital methemoglobinemia is unknown.

Causes

Autosomal recessive congenital methemoglobinemia is caused by mutations in the CYB5R3 gene. This gene provides instructions for making an enzyme called cytochrome b5 reductase 3. This enzyme is involved in transferring negatively charged particles called electrons from one molecule to another. Two versions

Frequently Asked Questions

For Type I, treatment often involves methylene blue, which helps convert methemoglobin back to normal hemoglobin, reducing cyanosis and improving oxygen delivery. Ascorbic acid (Vitamin C) may also be used as a milder reducing agent. For Type II, treatment is primarily supportive, focusing on managing neurological symptoms like seizures, dystonia, and developmental delays through therapies and medications, as methylene blue is not effective for the neurological aspects of this type.
Diagnosis typically involves a blood test to measure methemoglobin levels, which will be elevated. Further testing, such as an enzyme assay to check for cytochrome b5 reductase deficiency (the enzyme often responsible), and genetic testing to identify mutations in the CYB5R3 gene, can confirm the diagnosis and distinguish between Type I and Type II.
Daily management for Type I focuses on monitoring for cyanosis and administering methylene blue as needed, often leading to a normal life expectancy with good management. For Type II, daily management is much more intensive, involving comprehensive neurological care, physical and occupational therapy, speech therapy, and medications to manage seizures and movement disorders. The long-term outlook for Type II is significantly more challenging, with severe intellectual disability and a reduced life expectancy due to profound neurological impairment.
utosomal recessive means that a child must inherit two copies of the mutated gene (one from each parent) to develop the condition. If both parents are carriers (meaning they each have one normal and one mutated gene copy), there is a 25% chance with each pregnancy that their child will inherit two mutated copies and be affected, a 50% chance the child will be a carrier, and a 25% chance the child will inherit two normal copies and not be affected or a carrier.
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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