Transcobalamin Deficiency: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Transcobalamin Deficiency?
A primary care doctor, such as a pediatrician, is often the first to notice the signs and order early tests. A hematologist or medical geneticist often helps guide testing and long-term treatment. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What it is
Transcobalamin deficiency is a rare inherited condition. Transcobalamin is a protein that carries vitamin B12 through the blood to the cells that need it. Without enough of it, the body cannot use B12 from food, affecting the blood and nervous system.
Symptoms
Most babies show signs within the first few months of life. A common sign is anemia, which can make a baby look pale, weak, and feed poorly. Some develop diarrhea, frequent infections, or a swollen belly, and low B12 can delay development or cause movement problems.
Causes and who gets it
The condition is inherited when a child gets a changed TCN2 gene from both parents, who usually have no symptoms themselves. Because both parents must carry the changed gene, it is called autosomal recessive. It is very rare and affects boys and girls equally.
How doctors diagnose it
Doctors often start with blood tests, which can show anemia and unusually large red blood cells. A regular blood B12 test may look normal, because the problem is moving B12 into cells, not a lack of B12 in the blood. Genetic testing can confirm the diagnosis.
Treatment
Treatment focuses on getting usable vitamin B12 into the body, usually by injection, since shots bypass the transport problem better than pills. Treatment continues for life. With regular treatment, many children improve, though those treated late may have lasting effects on development.
When to see a doctor
See a doctor if a baby or young child is pale, weak, feeding poorly, or not growing as expected. Frequent infections or delays in sitting, crawling, or talking also deserve a checkup.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Either can be a steady partner for a rare condition, with longer visits, easier access, and help coordinating B12 injections and referrals.
Common questions
Is transcobalamin deficiency the same as a vitamin B12 deficiency?
They are related but not the same. In this condition, the body may have plenty of B12 in the blood but cannot move it into cells where it is needed. That is why standard B12 blood tests can be misleading.
Can adults get transcobalamin deficiency?
Symptoms almost always start in infancy, so it is usually found in babies and young children. Because it is inherited, adults who had it were very likely affected as infants too. Some milder cases may be found later in life, though this is uncommon.
Will my child need treatment forever?
Treatment is usually lifelong, since the body cannot fix the missing transport protein. The good news is that treatment is generally well tolerated. Doctors adjust the plan over time based on how the child is doing.
Can this condition be prevented?
There is no way to prevent an inherited gene change. Families with a history of the condition can talk to a genetic counselor, who explains how conditions are inherited and what testing options exist. Prenatal testing is possible for families who already have an affected child.
Sources
- NIH Genetic and Rare Diseases Information Center - Transcobalamin II deficiency
- MedlinePlus Genetics - Transcobalamin deficiency
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
