The AMN gene helps the small intestine take in vitamin B12 from food and helps the kidneys reclaim certain proteins instead of losing them in urine. This gene plays an important role in keeping red blood cells and nerves healthy. If it does not work properly, people can develop inherited vitamin B12 malabsorption, often with anemia, tiredness, pale skin, poor growth, or numbness. Some also have protein in the urine.
What is a gene?
A gene is a stretch of DNA that carries instructions your cells use to make molecules or direct processes in the body. Some genes hold the instructions for producing proteins, the parts of cells that do much of the work. Other genes mainly control when certain processes happen, where they happen, and how strongly they take place. Together, genes affect how the body develops and works, and they can influence how you respond to food, stress, or medications. For a more detailed look at this topic, you can learn more in the LearnHub.
Overview
AMNGene function
What if the gene works
The AMN gene helps your gut absorb vitamin B12 from food. It also supports the kidneys as they reclaim certain proteins from urine.
Risk
What if the gene does not work
Variants in the AMN gene can cause poor vitamin B12 absorption, often leading to megaloblastic anemia and sometimes developmental or nerve problems. Milder and more severe variants can affect when symptoms appear and how much urine protein shows up.
Treatment
What does that mean for your treatment
For people with a pathogenic variant in the AMN gene, treatment usually centers on lifelong vitamin B12 replacement, most often with regular injections because gut uptake is impaired. This guides drug choice toward parenteral hydroxocobalamin or cyanocobalamin rather than standard oral replacement alone.
Conditions associated with AMN
Gene function
What if the gene works
Your body relies on the AMN gene to absorb vitamin B12 from food and to reclaim useful proteins in the kidneys. It helps form a receptor on certain cell surfaces, especially in the small intestine and kidney tubules. Understanding how the AMN gene helps absorb vitamin B12 makes its day to day role easier to picture.
In the last part of the small intestine, AMN helps cells take in vitamin B12 after it has linked to intrinsic factor, a stomach made helper protein. This step lets the body move vitamin B12 from food into the bloodstream.
In kidney tubules, this gene helps cells recapture small proteins and other useful molecules that have been filtered into urine. That return system helps your body hold on to nutrients instead of losing them.
AMN works with cubilin to form a cell surface catcher that binds certain nutrients and proteins. It also helps pull that cargo into the cell so it can be processed and reused.
What is a variant?
A genetic variant is a minor change in a gene's DNA sequence. These changes are common and help shape normal human diversity, including differences in appearance, metabolism, and the way the body responds to environmental influences. Many variants do not have any noticeable effect and simply reflect natural genetic variation. Sometimes, though, a variant changes how a gene works more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
AMN gene variants can change how the cell makes, folds, or places the AMN protein, so it may not join its partner properly at the cell surface. This helps explain how AMN gene variants affect vitamin B12 absorption, because the receptor then works less well or not at all. Some variants only reduce activity, while more severe variants can stop the protein from being made or reaching the right place. That range often influences how early and how strongly Imerslund-Gräsbeck syndrome appears.
How variants are linked to conditions
Pathogenic variants in the AMN gene cause Imerslund-Gräsbeck syndrome, a rare inherited condition affecting vitamin B12 absorption. People with AMN gene variants linked to this condition may develop low vitamin B12, megaloblastic anemia, tiredness, poor growth, and sometimes protein in the urine. A confirmed disease-causing variant in both copies of the AMN gene can establish the diagnosis.
A variant is not necessarily a diagnosis
Genetic variants are a usual part of human biology and are common throughout the general population. Most do not have a direct effect on health and simply contribute to natural human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a confirmed diagnosis, especially when several genes and environmental factors are involved. In some cases, though, a single well characterized variant in a specific gene can be enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For AMN, risk is mainly shaped by inheritance rather than lifestyle. A child is most likely to have an AMN-related condition when they inherit a nonworking copy of the gene from both parents, and this is more likely when both parents are carriers or are blood relatives. There is not enough evidence to say that diet, exercise, or other daily habits change this genetic risk.
Inheritance of AMN variants
AMN-related conditions are inherited in an autosomal recessive pattern. This means a person usually develops the condition only if they inherit two changed copies of the AMN gene, one from each parent. Parents who carry one changed copy are typically unaffected carriers. For families asking how AMN gene variants are inherited, each pregnancy between two carriers has a 25% chance of an affected child, a 50% chance of a carrier child, and a 25% chance of a child with two usual copies.
What does my AMN result mean for my family?
For families with an AMN-related condition, close relatives may also carry the changed gene, even if they feel well. Brothers and sisters may be affected or may be carriers, and parents are usually carriers. Family members may want to review the result with a genetics professional to understand what it could mean for them and for future children.
Genetic information
Genetic testing
How you find out about variants
Genetic testing for AMN gene variants is done with a blood or saliva sample. A lab reads the DNA in the AMN gene to look for changes, then compares the result with known benign variants and disease causing variants to help clarify whether an AMN variant is present.
When should I consider getting a genetic test?
Consider genetic testing for AMN if there is unexplained vitamin B12 deficiency starting in childhood, especially with tiredness, poor growth, nerve symptoms, or protein in the urine, or if this runs in the family. Testing can help confirm an inherited cause and clarify risks for relatives.
A genetic result is only one part of your health story
A genetic result can provide useful insight, but what it tells you varies with the condition and the kind of variant involved. Over time, many factors, including age, medical history, lifestyle, and environment, influence how the body functions. For some conditions, especially those shaped by many genes, genetic information offers context rather than certainty and is best understood alongside other parts of care. In other situations, a genetic result can give a clear answer. In areas like medication response, genetic results can also help put personal experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how your body responds to medicines. Small differences in genes can change how a drug is absorbed, broken down, moved through the body, or how strongly it acts on its target. This helps explain why the same medication may work well for one person, seem less helpful for another, or cause more side effects in someone else.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in genes can shape the way a person responds to medications. It studies relationships between genes and drugs to better understand why the same treatment can work differently from one person to another. For many medicines, genes can influence how strongly a drug works or how the body handles it. This information can help support more informed and individualized treatment decisions. More information about this topic is available in the LearnHub.
Drugs influenced by the AMN gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how medicines will work, so any concerns about treatment, side effects, or ongoing symptoms are best discussed with your doctor.
History
AMN entered medical genetics through work on a rare inherited cause of vitamin B12 malabsorption, long recognized clinically as Imerslund-Gräsbeck syndrome. Families and communities once noticed patterns that seemed to pass from parent to child. In the early 2000s, researchers identified variants in the AMN gene as one cause of this condition, alongside findings in the CUBN gene. This helped connect older clinical observations with a specific genetic explanation and clarified why some affected families had similar symptoms despite living in different countries. From these first observations, research expanded steadily, and AMN became part of the modern picture of inherited vitamin B12 absorption conditions.