The KRT9 gene gives instructions for a keratin protein that strengthens the outer skin on the palms of the hands and soles of the feet. This gene helps your body handle daily pressure from walking, gripping, and friction. If you carry a disease-causing variant in the KRT9 gene, the skin in these areas may become unusually thick, hard, and prone to painful cracks, a condition called epidermolytic palmoplantar keratoderma.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate activities in the body. Some genes provide the directions for producing proteins, which do much of the work inside cells. Others mainly control when certain processes take place, where they occur, and how strongly they run. Together, genes affect how the body develops and works, and they can also influence how you respond to food, stress, and medications. For a deeper look at this topic, you can find more in the LearnHub.
Overview
KRT9Gene function
What if the gene works
The KRT9 gene helps make a keratin protein that strengthens the outer skin on the palms and soles. It supports skin cells as they handle pressure, rubbing, and daily wear.
Risk
What if the gene does not work
Variants in the KRT9 gene most often cause epidermolytic palmoplantar keratoderma, with thickened skin on the palms and soles. Milder to more severe variants can affect when it starts and how marked the skin changes are.
Treatment
What does that mean for your treatment
No KRT9-specific treatment or management approach is currently established. Care usually focuses on symptom relief rather than changing treatment based on a variant in the KRT9 gene, while research is exploring allele-specific RNA therapies that aim to reduce the effect of certain KRT9 variants.
Conditions associated with KRT9
Gene function
What if the gene works
Your palms and soles face constant pressure every day. In these areas, the KRT9 gene helps skin cells build sturdy inner support fibers so the thick skin on the palms of the hands and soles of the feet stays resilient. This supports everyday tasks like walking, standing, gripping, and handling objects.
The KRT9 gene gives palm and sole skin cells instructions for making keratin 9, a sturdy support protein. Keratin 9 joins with partner keratins to form support fibers inside the cell, helping it keep its shape during daily use.
In the thick outer skin of the hands and feet, these support fibers act like an internal mesh. They help cells stay connected and better withstand rubbing, gripping, and repeated pressure from walking or standing.
As skin cells move upward and mature, the KRT9 gene helps the palmoplantar epidermis (the thick skin of palms and soles) stay organized and strong. This supports a tough, protective surface used for touch, balance, and movement.
What is a variant?
A genetic variant is a small change in the DNA sequence of a gene. These changes are common and are part of normal human diversity, including differences in appearance, metabolism, and how the body responds to environmental influences. Many variants have no noticeable effect and simply represent natural genetic variation. In some cases, however, 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 KRT9 gene can make keratin 9 less stable, so skin cells in the palms and soles form a weaker internal support network. This helps explain how KRT9 gene variants influence protein function: many alter a single building block and disrupt how keratin fibers assemble, while more disruptive changes can interfere more strongly with the protein’s shape and interactions. Milder variants may cause less functional disturbance, while stronger ones can be linked to earlier or more noticeable palm and sole skin thickening.
How variants are linked to conditions
Pathogenic variants in the KRT9 gene cause epidermolytic palmoplantar keratoderma, an inherited condition that leads to thickened skin on the palms and soles, often from early childhood. This is the main well-established diagnosis linked to the KRT9 gene, and finding a disease-causing variant can confirm it.
A variant is not necessarily a diagnosis
Genetic variants are common across the general population and are a normal feature of human biology. Most do not directly affect health and simply reflect natural variation among people. For many genes, having a variant associated with a condition indicates a possible link rather than a certain diagnosis, particularly when several genes and environmental influences play a role. In contrast, some diagnoses can be confirmed by a single well-established variant in a particular gene.
Are there things that can increase or change my risk?
For KRT9, the chance of having this palm-and-sole skin condition is mostly set by the gene change itself, which often runs in families. Friction, pressure, heat, and sweating can make thickened skin and discomfort worse, but they do not change whether the gene variant is present. Regular skin care and reducing rubbing can help limit symptoms and complications.
Inheritance of KRT9 variants
For families looking into how variants of the KRT9 gene are inherited, the well-established pattern is autosomal dominant. This means a person with a disease-causing variant in one copy of the KRT9 gene can pass it to a child, whether the child is a son or a daughter. Each child has a 50% chance of inheriting that variant. In most affected families, the variant is passed down from an affected parent.
What does my KRT9 result mean for my family?
For KRT9, a disease-causing result usually means close relatives may also carry the same gene change, especially a parent, brother, sister, or child. In families with a KRT9-related skin condition, each child of an affected parent has a 1 in 2 chance of inheriting it. Family members who have thick, painful skin on the palms and soles may want to discuss whether the same result could apply to them.
Genetic information
Genetic testing
How you find out about variants
KRT9 genetic testing uses a blood sample or cheek swab to read the KRT9 gene and look for variants linked to inherited thick skin on the palms. This test usually works by sequencing, which checks the gene’s letter by letter code, and the result may help confirm whether a KRT9 variant is present.
When should I consider getting a genetic test?
Genetic testing for the KRT9 gene can be helpful if thick, painful skin on the palms and soles starts in childhood, especially when other family members have similar skin changes. A confirmed change in KRT9 can explain the condition and help clarify the chance of it running in the family.
A genetic result is only one part of your health story
A genetic result can provide useful insight, but how much it explains 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 affected by many genes, genetic information offers context rather than certainty and is best understood together with other parts of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic results can also help put personal experiences into perspective.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Two people can take the same treatment and have different results because their bodies may absorb, break down, or respond to the drug in different ways. These inherited differences are common and can influence how well a medicine works or how sensitive someone is to side effects. Medication response also depends on other factors, including age, liver and kidney function, and other medicines being taken.
What is Pharmacogenetics?
Pharmacogenetics looks at how genetic differences can shape a person’s response to medications. It studies the relationship between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medicines, genes can affect how strongly a drug works or how the body processes it. This information can support more informed, more personalized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the KRT9 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding how medicines are chosen or used, so questions about symptoms, side effects, or treatment are best discussed with your doctor.
History
KRT9 entered medical genetics through studies of families with thickened skin on the palms and soles, a pattern doctors had documented long before the gene itself was identified. In the 1990s, researchers connected this inherited skin condition to variants in the KRT9 gene, helping show that specific keratin genes could be tied to distinct skin conditions. From these first observations, research expanded steadily, and KRT9 became a clear example of how changes in structural skin genes can run in families. These findings also helped refine the classification of palm and sole keratin conditions that had previously been grouped mainly by appearance. Over time, KRT9 became part of the broader story of how gene discovery transformed dermatology from description alone to precise genetic diagnosis.