This gene helps your body turn part of the amino acid tryptophan into NAD, a molecule your cells use for energy and repair. The HAAO gene makes a protein that supports this step and helps keep certain chemical byproducts from building up. If the gene does not work well, NAD levels may drop and these byproducts may rise, which can affect brain development and movement. Pathogenic variants in the HAAO gene are linked to a very rare inherited neurologic condition.
What is a gene?
Genes are stretches of DNA that carry instructions your cells use to make molecules or manage processes throughout the body. Some provide the code for proteins, which do much of the cell’s work. Others are mainly involved in regulating when certain processes happen, where they happen, and how active they are. Taken together, genes affect how your body develops and functions, and they can also influence how you respond to food, stress, or medicines. For a deeper look at this topic, you can read more in the LearnHub.
Overview
HAAOGene function
What if the gene works
The HAAO gene helps your body break down tryptophan, a protein building block. Its protein supports a pathway that helps make NAD, a molecule cells use to release energy and stay healthy.
Risk
What if the gene does not work
Milder to more severe variants in the HAAO gene can cause a rare inherited condition affecting early development, often with brain, kidney, heart, or spine differences; severity and the age symptoms appear can vary.
Treatment
What does that mean for your treatment
No HAAO-specific treatment or drug-selection approach is currently established in clinical guidelines for people with pathogenic variants in the HAAO gene. The HAAO gene is part of the kynurenine pathway, which is being studied as a possible drug target and biomarker in neurologic disease, immune conditions, and some cancers.
Conditions associated with HAAO
Gene function
What if the gene works
Your cells use the HAAO gene during the normal breakdown of tryptophan, a building block from protein in food. Its protein helps move this pathway forward so cells can make NAD, a helper molecule needed for energy and many everyday reactions. This is part of what the HAAO gene does in the body each day.
The HAAO gene helps your cells process one of the small compounds made as tryptophan is broken down. This keeps the pathway moving in an orderly way.
Through this pathway, the HAAO gene contributes to making NAD, a molecule cells need to release energy from food and carry out routine chemical work. This supports day to day cell activity across the body.
Inside your cells, the HAAO gene turns one step in this chemical pathway into the next so later products can be formed. By doing so, it helps keep normal cell chemistry on track.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These changes are common and help shape normal human diversity, including differences in appearance, metabolism, and how the body responds to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some cases, though, a variant can change how a gene functions more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the HAAO gene can change the enzyme’s shape, stability, or amount, so cells break down 3-hydroxyanthranilic acid less effectively. Milder variants may leave some activity, while more severe variants can sharply reduce activity or stop the enzyme from being made. This range helps explain how HAAO gene variants affect enzyme activity, with buildup of pathway chemicals and less NAD (a molecule cells use for energy and repair).
How variants are linked to conditions
Among HAAO gene variants linked to congenital malformations, the clearest association is vertebral, cardiac, renal, and limb defects syndrome 3, a rare inherited condition. Pathogenic variants in both copies of the HAAO gene cause this condition and can confirm the diagnosis. Babies with this HAAO-related condition may be born with changes in the spine, heart, kidneys or urinary tract, and arms or legs.
A variant is not necessarily a diagnosis
Variants in genes are a normal feature of human biology and are common across 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 indicates a possible link rather than a definite diagnosis, especially when several genes and environmental factors are involved. In some situations, however, a single well-characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
There is not yet broadly confirmed evidence on specific factors that increase or reduce health risk related to the HAAO gene. For many living with an HAAO gene change, risk appears to depend mainly on the exact genetic variant rather than everyday habits, so personal guidance from a doctor or genetic counselor is the best next step.
Inheritance of HAAO variants
There is not yet a broadly confirmed disease inheritance pattern tied to the HAAO gene in routine clinical genetics, so answers about how HAAO gene variants are inherited remain cautious and may evolve as research grows. The HAAO gene is located on chromosome 2, which is an autosome. That means each person inherits two copies of the HAAO gene, one from their mother and one from their father.
What does my HAAO result mean for my family?
For HAAO, the best-known health condition linked to the gene follows a recessive pattern in families. This usually means parents can be healthy carriers, and brothers or sisters may also be affected or be carriers. Other close relatives, such as future children of siblings, may also want to know there could be a carrier chance in the family.
Genetic information
Genetic testing
How you find out about variants
HAAO genetic testing looks for variants in the HAAO gene from a blood sample, saliva sample, or cheek swab. A lab reads your DNA code and compares it with the usual sequence to see whether a variant is present, either through a single-gene test or as part of a broader gene panel.
When should I consider getting a genetic test?
There is not yet a broadly established HAAO-specific reason for routine genetic testing. Decisions about testing are usually based on your personal health history, symptoms, and family history, often with guidance from a doctor or genetic counselor.
A genetic result is only one part of your health story
Genetic results can provide meaningful insight, although how much they reveal depends on the condition and the kind of variant involved. How the body functions over time is also shaped by many factors, including lifestyle, environment, age, and medical history. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best considered alongside other parts of care. In other situations, a genetic result may offer a clear answer. In areas such as medication response, genetic results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Small differences in DNA can change how the body breaks down a drug, moves it through the bloodstream, or responds to it at its target. This helps explain why the same treatment works well for one person, has little effect for another, or causes more side effects in someone else. These differences are common and are one of several factors, along with age, kidney and liver function, and other medicines, that can shape medication response.
What is Pharmacogenetics?
Pharmacogenetics is the area of study focused on how genetic differences shape responses to medications. It examines connections between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medications, genes affect either how strongly a drug works or how the body handles it. This information can support treatment decisions that are more informed and more individualized. More detail on this topic is available in the LearnHub.
Drugs influenced by the HAAO gene
When should I seek medical advice?
There is no broadly confirmed role for this gene in predicting how medicines will work, so general questions about side effects, medicine choice, or other health concerns are best discussed with your doctor.