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TCN2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

TCN2 gene

The TCN2 gene provides instructions for making the protein transcobalamin, which is essential for transporting vitamin B12 from the bloodstream into cells throughout the body.

Normal Function

The TCN2 gene provides instructions for making a protein called transcobalamin (formerly known as transcobalamin II). This protein transports cobalamin (also known as vitamin B12) from the bloodstream to cells throughout the body. Cobalamin is obtained from the diet; this vitamin is found in animal products such as meat, eggs, and shellfish.

During digestion, cobalamin is transported through intestinal cells into the bloodstream. Transcobalamin attaches (binds) to cobalamin when it is released into the bloodstream and transports the vitamin to cells. The transcobalamin-cobalamin complex binds to a receptor on the cell surface, which allows the complex to enter the cell. Transcobalamin releases cobalamin when the complex enters the cell and transcobalamin is broken down.

Within cells, cobalamin helps certain enzymes carry out chemical reactions. Cobalamin plays a role in the processes that produce the building blocks of DNA (nucleotides) and break down various compounds such as fatty acids; these processes are needed for cell growth and division (proliferation) and cellular energy production. Cobalamin's role in these processes is particularly important in the formation of new blood cells and in the nervous system.

Health Conditions Related to Genetic Changes

Transcobalamin deficiency

More than 20 mutations in the TCN2 gene have been found to cause transcobalamin deficiency. This condition impairs the transport of cobalamin from the bloodstream to cells throughout the body. Affected individuals have difficulty gaining weight and growing at the expected rate (failure to thrive), vomiting, diarrhea, a shortage of all types of blood cells, and neurological problems. Many TCN2 gene mutations lead to a complete or near-complete lack (deficiency) of transcobalamin. Other TCN2 gene mutations result in a transcobalamin protein that cannot bind to cobalamin or a protein that cannot bind to the receptor at the surface of cells. The resulting lack of cobalamin within cells interferes with the functioning of certain enzymes, which impacts many cell activities.

Other Names for This Gene

  • D22S676
  • D22S750
  • TC
  • TC II
  • TC-2
  • TC2
  • TCII
  • transcobalamin II
  • transcobalamin-2

Frequently Asked Questions

In infants and children, early signs of transcobalamin deficiency often include difficulty gaining weight and growing at the expected rate (failure to thrive), frequent vomiting, and diarrhea. As the condition progresses, a shortage of all types of blood cells can lead to symptoms like unusual paleness, fatigue, or frequent infections. Neurological problems may also develop, presenting as developmental delays or unusual movements. You should be concerned and seek medical attention promptly if your child exhibits any of these symptoms, especially if they are not thriving or show signs of anemia or neurological issues.
The standard treatment for transcobalamin deficiency involves lifelong vitamin B12 (cobalamin) supplementation, typically administered through injections. This bypasses the dysfunctional transcobalamin transport system, ensuring cells receive the necessary vitamin. With early diagnosis and consistent, appropriate treatment, many affected individuals can achieve normal growth and development, and live a relatively normal life. Regular monitoring of B12 levels and overall health is essential to adjust treatment as needed and manage any potential complications.
Transcobalamin deficiency is typically diagnosed through a combination of blood tests. These tests measure levels of vitamin B12 (cobalamin), homocysteine, and methylmalonic acid, which are often abnormal in this condition. Specifically, low levels of transcobalamin protein in the blood can be measured. Genetic testing of the TCN2 gene can confirm the diagnosis by identifying specific mutations. Early diagnosis is crucial for prompt treatment and to prevent long-term complications.
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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