The PHYH gene helps your body break down phytanic acid, a type of fat that comes from foods such as dairy products, beef, lamb, and some fish. If this gene does not work properly, phytanic acid can build up and affect tissues, especially the nerves, eyes, skin, and heart. People with harmful variants in the PHYH gene can develop adult Refsum disease, which may lead to night blindness, balance problems, numbness, hearing loss, and dry, scaly skin.
What is a gene?
Genes are stretches of DNA that carry instructions your cells use to make molecules or guide processes in the body. Some genes provide the directions for making proteins, the parts of cells that do the work. Others mainly regulate when certain processes happen, where they take place, and how strongly they operate. Together, genes affect how the body develops and works, and they can influence how you respond to food, stress, and medications. For a closer look at this topic, you can learn more in the LearnHub.
Overview
PHYHGene function
What if the gene works
The PHYH gene helps your cells break down phytanic acid, a type of fat that comes from foods such as dairy, beef, and some fish. This helps prevent buildup and supports healthy nerves, eyes, and other tissues.
Risk
What if the gene does not work
Disease-causing variants in the PHYH gene can lead to adult Refsum disease, which often affects vision, smell, hearing, balance, skin, and the nerves. Milder and more severe variants can influence when signs begin and which features are most noticeable.
Treatment
What does that mean for your treatment
Pathogenic variants in the PHYH gene support lifelong treatment aimed at lowering phytanic acid, mainly a strict low phytanic acid diet and avoiding fasting or rapid weight loss. During sudden worsening, plasma exchange or lipid apheresis can help lower phytanic acid levels. No PHYH-specific drug therapy is established.
Conditions associated with PHYH
Gene function
What if the gene works
Your cells use the PHYH gene to process a specific dietary fat called phytanic acid. This fat comes mainly from foods such as dairy, beef, lamb, and some fish. When the PHYH gene is working properly, it helps your body handle this fat through a controlled step inside the cell.
The PHYH gene helps your cells start breaking down phytanic acid, a fat found mainly in dairy, beef, lamb, and some fish. This first step makes the fat easier for the body to process further.
Inside small cell compartments called peroxisomes, the PHYH gene provides instructions for a protein that carries out phytanic acid breakdown in peroxisomes. This keeps the process organized and in the right part of the cell.
Some fats cannot go through the body’s usual fat processing pathway right away. The PHYH gene supports a backup route called alpha oxidation, which trims phytanic acid so other enzymes can continue the job.
What is a variant?
A genetic variant is a minor change in a gene’s DNA sequence. These changes are common and are part of normal human diversity, including differences in appearance, metabolism, or the way the body responds to environmental influences. Many have no noticeable effect and simply represent natural genetic variation. In some cases, though, a variant changes how a gene works more substantially and can contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the PHYH gene can alter the enzyme’s shape, stability, or ability to work inside peroxisomes, the small cell compartments that handle certain fats. In simple terms, how variants in the PHYH gene affect protein function can range from a partial drop in activity to almost none. Milder variants may leave some activity, while more severe variants often lead to greater phytanic acid buildup and can be linked to earlier or more noticeable Refsum disease features.
How variants are linked to conditions
Pathogenic variants in the PHYH gene cause adult Refsum disease, a rare inherited condition. This condition often affects vision and can also involve hearing, balance, nerves, skin, and heart rhythm. PHYH gene variants and adult Refsum disease are the main well-established clinical link for this gene. When two disease-causing variants are found in the right clinical setting, they can confirm the diagnosis.
A variant is not necessarily a diagnosis
Across the general population, genetic variants are common and form a normal part of human biology. Most have no direct impact on health and simply represent natural human diversity. For many genes, carrying a variant associated with a condition suggests a possible link rather than a certain diagnosis, especially when several genes and environmental factors also play a role. In some cases, though, one well-characterized variant in a specific gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For PHYH-related Refsum disease, risk is mainly set by whether someone inherits two nonworking copies of the PHYH gene. Diet does not change whether you have the condition, but eating foods high in phytanic acid can raise blood levels and make problems more likely or harder to control. Care often focuses on avoiding those triggers and watching for complications early.
Inheritance of PHYH variants
PHYH-related Refsum disease is inherited in an autosomal recessive pattern. This means a person usually needs to inherit two disease-causing variants in the PHYH gene, one from each parent, to have the condition. Parents who each carry one PHYH gene variant are typically unaffected carriers, and with each pregnancy they have a 25% chance of having an affected child, a 50% chance of having a child who is a carrier, and a 25% chance of having a child with neither variant. When people look into how PHYH variants are inherited, this carrier pattern is the key point.
What does my PHYH result mean for my family?
For families of someone with a disease-causing PHYH result, the pattern is usually recessive, which means parents are often healthy carriers. Brothers and sisters may also be carriers, and in some families a sibling could also have the condition. More distant relatives on either side of the family may carry the same change too, especially if there is a family history of similar symptoms.
Genetic information
Genetic testing
How you find out about variants
PHYH genetic testing uses a blood or saliva sample to read your DNA and look for variants linked with adult Refsum disease. To find out about variants in the PHYH gene, a lab checks whether you carry one changed copy or two variants that can confirm the diagnosis. Results are read alongside your symptoms and family history.
When should I consider getting a genetic test?
Consider PHYH genetic testing if you or a family member has signs of Refsum disease, such as night blindness, balance problems, numbness, hearing loss, or high levels of a fatty substance called phytanic acid on blood tests. It can also help relatives understand their chance of having or carrying a change in the PHYH gene.
A genetic result is only one part of your health story
A genetic finding can provide useful insight, but how much it can clarify varies with the condition and the kind of variant involved. Factors such as lifestyle, environment, age, and medical history also influence how the body functions over time. For some conditions, especially those shaped by many genes, genetic information offers context rather than certainty and is best understood together with other aspects of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic information can help put individual experiences into perspective.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. This helps explain why the same medication works well for one person, seems less effective for another, or causes more side effects in someone else. Part of the reason is that the body can absorb, break down, transport, or respond to a drug differently based on inherited differences in genes, and these differences are common.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic differences affect a person’s response to medications. By looking at connections between genes and drugs, it helps explain why the same treatment can work differently from one person to another. For many medicines, genes influence how strongly a drug works or how the body processes it. This information can support treatment decisions that are more informed and more individualized. You can learn more about this topic in the LearnHub.
Drugs influenced by the PHYH gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how people respond to medicines, so questions about side effects, new symptoms, or treatment choices are best discussed with your doctor.
History
Refsum disease was first described in the 1940s by the Norwegian neurologist Sigvald Refsum, long before its genetic cause was known. For many years, researchers linked the condition to a buildup of phytanic acid in the body, which helped narrow the search for the responsible gene. Building on this early work, scientists identified the PHYH gene in the late 1990s as a key cause of the classic adult form of Refsum disease. Early papers often referred to it as PAHX, and that older name still appears in some medical literature. This discovery gave families a clearer explanation for an inherited condition that had once been recognized only by its pattern of symptoms.