The HPD gene helps your body break down tyrosine, an amino acid from food that is used to build proteins. If this gene does not work properly, tyrosine and related substances can build up in the body. Pathogenic variants in the HPD gene can cause a rare condition called tyrosinemia type III, which may be linked to developmental delay, seizures, or problems with balance and coordination. Some people with HPD gene changes have only mild symptoms.
What is a gene?
Genes are sections of DNA that store instructions your cells use to make molecules or to regulate what happens in the body. Some carry the code for proteins, the parts of cells that do much of the work. Others mainly direct when specific processes take place, where they occur, and how strongly they operate. In combination, genes affect how the body develops and functions, and they can shape how you respond to food, stress, or medications. To explore this subject more closely, you can learn more in the LearnHub.
Overview
HPDGene function
What if the gene works
The HPD gene helps your body break down tyrosine, an amino acid from food. Its protein works mainly in the liver to turn tyrosine into substances your cells can use or clear.
Risk
What if the gene does not work
Changes in the HPD gene can cause tyrosinemia type III, which may involve seizures, balance problems, or learning difficulties. Other HPD variants can cause hawkinsinuria, and effects can range from mild to more noticeable.
Treatment
What does that mean for your treatment
For harmful variants in the HPD gene, treatment is usually dietary rather than drug based. A diet low in tyrosine and phenylalanine can help lower tyrosine levels and may reduce symptoms, and no HPD-specific medicine is currently established.
Conditions associated with HPD
Gene function
What if the gene works
Your liver uses the HPD gene to help process tyrosine, an amino acid that comes from protein in food. Its protein carries out an early step in turning tyrosine into smaller substances your body can use or clear. Understanding how the HPD gene helps break down tyrosine makes its role in everyday amino acid balance easier to see.
The HPD gene helps your body break down tyrosine, an amino acid from food and normal protein turnover. This is an early, routine step in how cells handle leftover amino acids.
Its protein converts one tyrosine byproduct into the next one so the breakdown pathway can keep moving. This handoff lets later steps finish processing the material.
By supporting tyrosine handling, the HPD gene helps maintain a steady balance of amino acids and their byproducts, mainly in the liver. That supports normal day to day processing of protein after you eat.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These changes are common and help explain normal human diversity, such as differences in appearance, metabolism, or the way the body responds to environmental influences. Many have no noticeable effect and are simply part of natural genetic variation. In some cases, however, 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
HPD gene variants often change the enzyme’s shape or stability, so it breaks down tyrosine less effectively. Some variants leave partial activity, while more disruptive variants can greatly reduce or nearly stop the enzyme’s action. This functional effect of HPD gene variants may help explain why tyrosinemia type III can vary, with lower activity often linked to earlier or more marked features. A few variants can also alter the enzyme’s chemistry rather than simply lowering it.
How variants are linked to conditions
Pathogenic variants in the HPD gene can cause tyrosinemia type III, a rare inherited condition linked to high tyrosine levels and sometimes seizures, balance problems, or learning difficulties. Certain HPD gene variants also cause hawkinsinuria, another rare inherited condition usually identified in infancy. These are rare diagnoses, and a confirmed pathogenic variant in the HPD gene can help establish the diagnosis.
A variant is not necessarily a diagnosis
Genetic variants are a usual part of human biology and are widespread in the general population. Most do not directly affect health and instead reflect natural human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a definite diagnosis, especially when multiple genes and environmental factors also play a role. In some situations, though, a single well-characterized variant in a particular gene can be enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For HPD, risk is mainly shaped by inheritance rather than lifestyle. A child’s chance of having an HPD-related condition is higher when both parents carry a harmful HPD variant, and this can be more likely in families with a known history or where parents are related by blood. There is not enough evidence to say that diet, exercise, or other everyday habits change the chance of inheriting it.
Inheritance of HPD variants
The inheritance of HPD gene variants depends on the specific HPD-related condition. Some HPD gene variants follow an autosomal recessive pattern, which means a child inherits one altered copy from each parent, while others are inherited in an autosomal dominant pattern, where one altered copy from one parent can be enough to cause the condition. This mixed pattern is the key point in how HPD gene variants are inherited within families. A parent with a dominant HPD-related condition can pass it to a son or daughter, and parents who each carry a recessive variant can have children who are affected.
What does my HPD result mean for my family?
For HPD, what this means for relatives depends on which HPD-related condition is tied to the result. Some HPD changes are linked to a condition that can run in families in a dominant way, so close relatives may also carry the same change, while other HPD changes cause a recessive condition, where parents may be healthy carriers and siblings could also be affected or be carriers. Family implications are different for these two situations.
Genetic information
Genetic testing
How you find out about variants
To look for changes in the HPD gene, a lab usually uses a blood sample or saliva sample for genetic testing for HPD variants. The lab reads the gene’s DNA code, and some tests also check for missing or extra pieces. Results may show no variant, a benign variant, or a variant linked to disease.
When should I consider getting a genetic test?
Genetic testing for the HPD gene may be considered if a child has signs of a rare condition that affects how the body breaks down part of protein, such as seizures, trouble with balance, or learning problems, especially with high tyrosine on blood or urine tests. It can also help when this condition runs in the family.
A genetic result is only one part of your health story
A genetic finding can provide useful insight, but how much it explains varies based on the condition and the type of variant identified. Many factors, including lifestyle, environment, age, and medical history, also shape how the body works over time. In some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is most helpful when viewed alongside other parts of care. In other situations, a genetic result can offer a clear answer. In areas like 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. Some people break down a drug faster or more slowly, while others may be more or less sensitive to its effects. This helps explain why the same treatment can work well for one person but less well for another, or why side effects differ from person to person. These differences are common and are one part of how the body handles medication.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in a person’s genes can affect the way they respond to medicines. It studies links between genes and medications to clarify why the same treatment may work differently in different people. For many drugs, genes help shape both how strongly a medicine works and how the body handles it. This information can support treatment choices that are more informed and more personalized. To learn more about this subject, visit the LearnHub.
Drugs influenced by the HPD gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medication choice or dosing, so general questions about medicines, side effects, or your health are best discussed with your doctor.
History
Inherited patterns in tyrosine breakdown were noticed long before the HPD gene was identified. Early clinicians described rare family cases of tyrosinemia and later recognized that not all forms had the same cause. From these first observations, research expanded steadily. In the late 20th century, scientists linked variants in the HPD gene to tyrosinemia type III and to hawkinsinuria, helping separate these conditions from other causes of high tyrosine levels. This clarified diagnosis for families and improved the way related metabolic conditions were classified. Over time, descriptions became more precise as genetic testing connected older clinical reports with changes in the HPD gene.