The PHEX gene helps control phosphate, a mineral your body needs to build strong bones and teeth. When this gene does not work properly, the kidneys let too much phosphate leave in urine, which can lead to soft bones, bowed legs, bone pain, short stature, and dental problems. In medicine, this gene is best known for its link to X-linked hypophosphatemia, an inherited condition that often begins in childhood.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes hold the information needed to produce proteins, the parts of cells that do the work. Other genes mainly guide when certain processes happen, where they occur, and how strongly they operate. Together, genes affect how the body develops and functions, and they can also influence how you respond to food, stress, or medications. For a more detailed look at this topic, you can read more in the LearnHub.
Overview
PHEXGene function
What if the gene works
The PHEX gene helps control phosphate levels in the body. This supports normal hardening of bones and teeth as children grow and adults maintain bone strength.
Risk
What if the gene does not work
Variants in the PHEX gene usually cause X-linked hypophosphatemia, where low phosphate leads to soft bones, bowed legs, short stature, and dental problems. Milder and more severe variants can influence how early features appear and how marked they are.
Treatment
What does that mean for your treatment
For people with a pathogenic or loss-of-function variant in the PHEX gene, treatment may include burosumab, a targeted medicine used in current guidelines. Some still use phosphate and active vitamin D, especially when burosumab is not suitable. Care also includes regular checks of phosphate levels, kidneys, and bone health.
Conditions associated with PHEX
Gene function
What if the gene works
The PHEX gene helps your body manage phosphate, a mineral needed to build and maintain strong bones and teeth. It is especially active in cells that make and maintain bone and tooth tissue. Understanding what the PHEX gene does in bones and teeth helps explain its steady role in everyday growth and mineral balance.
The PHEX gene helps control signals that regulate how your body handles phosphate. It helps keep FGF23, a hormone that tells the kidneys how much phosphate to save, in an appropriate range.
In bone, the PHEX gene supports the normal buildup of minerals into the bone structure. This helps bones develop and maintain the firm, supportive framework your body relies on every day.
The PHEX gene is active in cells that build dentin, the hard layer under tooth enamel. By supporting normal mineral use in teeth, it helps teeth form with the strength and structure they need.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These differences are common and help make up normal human diversity, such as variation in appearance, metabolism, or the way the body responds to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change a gene’s function more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the PHEX gene can change the protein’s shape, shorten it, or keep cells from placing it correctly on the cell surface, so it works less well or not at all. This overview of how PHEX gene variants affect protein function includes milder changes that partly reduce activity and more severe variants that lead to a missing or broken protein. In X-linked hypophosphatemia, these differences can help explain why symptoms may begin earlier or be more noticeable in some people.
How variants are linked to conditions
Pathogenic variants in the PHEX gene cause X-linked hypophosphatemia. PHEX gene variants linked to X-linked hypophosphatemia can confirm the diagnosis in a person with suggestive symptoms. Many children develop rickets, bowed legs, slow growth, or dental abscesses, while some adults have bone pain, osteomalacia, joint stiffness, or fractures.
A variant is not necessarily a diagnosis
Genetic variants are a routine part of human biology and are widespread in the general population. Most have no direct impact on health and simply reflect natural variation among people. For many genes, carrying a variant associated with a condition suggests a possible link rather than a certain diagnosis, especially when more than one gene and environmental factors play a role. In some situations, though, 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?
For PHEX, risk is mainly set by whether a disease-causing gene change is inherited, rather than by lifestyle. If a parent carries a PHEX change, each child has a 50% chance of inheriting it. How strongly it affects someone can vary, and early treatment and monitoring can help limit bone and dental problems.
Inheritance of PHEX variants
PHEX-related conditions are usually inherited in an X-linked dominant pattern, which is the main answer to how PHEX gene variants are inherited. If a mother carries a disease-causing variant in the PHEX gene, each child has a 50% chance of inheriting it. If a father carries the variant, all daughters and none of his sons inherit it. Some people with a PHEX gene variant are the first in their family to have it because the variant arose new and was not inherited from either parent.
What does my PHEX result mean for my family?
PHEX changes are most often linked to X-linked hypophosphatemia, so close relatives may also carry the same change. A parent with the result can pass it on to children, and brothers, sisters, and other relatives on the same side of the family may also want to learn whether they carry it. Some cases happen for the first time in one person, so a parent does not always have the same gene change.
Genetic information
Genetic testing
How you find out about variants
PHEX genetic testing for X-linked hypophosphatemia usually starts with a blood or saliva sample. A lab reads the PHEX gene to look for variants, and the result can help show whether you carry a pathogenic variant or whether a known family variant is present.
When should I consider getting a genetic test?
Consider PHEX testing if you or your child has ongoing low phosphate with bowed legs, bone pain, delayed growth, frequent dental abscesses, or a family history of X-linked hypophosphatemia. A confirmed PHEX change can help explain the cause and support care for related bone and tooth problems.
A genetic result is only one part of your health story
A genetic result can provide useful insight, but how much it explains varies with the condition and the kind of variant involved. Lifestyle, environment, age, and medical history, among other factors, shape how the body functions over time. In some conditions, especially those influenced by many genes, genetic information adds context rather than certainty and is best understood together with 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 perspective.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. This is one reason the same treatment may work well for one person but less well for another, or cause more side effects in some people. Small differences in genes can change how the body breaks down, moves, or responds to a drug, which can influence how effective it feels and how sensitive someone is to it.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in genes affect the way people respond to medicines. It studies links between genes and medications to help explain why the same treatment can work differently in different people. For many drugs, genes can influence how strongly a medicine works or how the body handles it. This information can support more informed and more personalized treatment decisions. More detail on this topic is available in the LearnHub.
Drugs influenced by the PHEX gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting medication response, so questions about medicines, side effects, or treatment changes are best discussed with your doctor.
History
Long before the gene was identified, doctors described families in which children developed bowed legs and poor growth from low phosphate levels, a pattern later recognized as X linked hypophosphatemia. Inheritance patterns were noticed long before the gene was identified. In the late 20th century, researchers mapped the cause to the X chromosome and, in 1995, identified the PHEX gene. That discovery gave families and clinicians a clearer explanation for a condition that had been recognized for decades but not fully understood. From these first observations, research expanded steadily. The PHEX gene became an important milestone in the study of inherited low phosphate conditions and helped shape modern genetic diagnosis for this group of conditions.