The PYGL gene helps the liver break down stored glycogen into glucose, especially between meals and overnight. If it is not working well, the liver may struggle to release enough sugar, which can lead to low blood sugar, ketones, an enlarged liver, and slower growth in childhood. This gene plays an important role in keeping energy supply steadier when food is not coming in. Pathogenic variants in the PYGL gene cause glycogen storage disease type VI, also called Hers disease.
What is a gene?
Genes are sections of DNA that give your cells instructions for making molecules or managing processes in the body. Some genes hold the information needed to make proteins, the parts of cells that do the work. Others mainly guide when certain processes happen, where they take place, and how active they are. Together, genes affect how the body develops and works, and they can also shape how you respond to food, stress, and medications. More detail on this topic is available in the LearnHub.
Overview
PYGLGene function
What if the gene works
The PYGL gene helps the liver break down stored glycogen into glucose. This supports a steady blood sugar level between meals and during fasting.
Risk
What if the gene does not work
Certain variants in the PYGL gene can cause glycogen storage disease type VI, often with an enlarged liver, low blood sugar, and poor growth in childhood. Milder or severe variants can affect when features appear and how marked they are.
Treatment
What does that mean for your treatment
A pathogenic or loss-of-function variant in the PYGL gene usually points to supportive metabolic treatment rather than a gene-directed drug. Care often centers on avoiding long fasts, using regular meals, and, for some people, adding uncooked cornstarch or extra protein to help keep blood sugar steadier. No PYGL-specific medicine is currently established in routine guidelines.
Conditions associated with PYGL
Gene function
What if the gene works
In your liver, the PYGL gene helps manage the sugar your body has stored for later use. It gives cells instructions for a protein that breaks down glycogen, the liver’s packed away form of sugar, when your body needs a steady supply between meals. This is part of what the PYGL gene does in the liver every day.
The PYGL gene helps liver cells break down glycogen, the stored form of sugar. This turns a large sugar reserve into smaller units that can be processed and used when your body needs fuel.
By helping the liver draw on its sugar stores, this gene supports a steadier blood sugar level between meals and during overnight fasting. That ongoing supply helps tissues such as the brain keep getting fuel.
Its protein becomes more active when the body signals that extra fuel is needed, such as during fasting or physical activity. This lets the liver respond in a controlled way rather than releasing stored sugar all at once.
What is a variant?
A genetic variant is a minor difference in the DNA sequence of a gene. Variants are common and are one reason people differ in normal ways, such as appearance, metabolism, or how the body reacts to environmental influences. Many have no noticeable effect at all and are simply part of natural genetic variation. At times, though, a variant can change a gene’s function more strongly and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the PYGL gene can change the shape, stability, or amount of liver glycogen phosphorylase, so liver cells break down stored glycogen less effectively. Some PYGL gene variants leave partial enzyme activity, while more disruptive changes can nearly abolish it. This range helps explain why glycogen storage disease type VI may be milder in some people and more noticeable or earlier in others.
How variants are linked to conditions
Pathogenic variants in the PYGL gene cause glycogen storage disease type VI, also called Hers disease. This inherited liver condition is linked to low blood sugar, an enlarged liver, slow growth in childhood, and sometimes mild delays in puberty. Many people with PYGL gene changes have a relatively mild course, though symptoms and test results can vary from person to person. A confirmed PYGL gene diagnosis helps explain these findings.
A variant is not necessarily a diagnosis
Across the general population, genetic variants are common and are a normal part of human biology. Most do not have a direct effect on health and instead reflect natural human diversity. For many genes, carrying a variant associated with a condition indicates a possible link rather than a definite diagnosis, particularly when several genes and environmental factors play a role. Still, in some situations, a single well-characterized variant in a specific gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For PYGL-related glycogen storage disease, risk is mainly set by whether a child inherits a changed copy of the PYGL gene from both parents. Family history can make the chance higher within a family. There is not broadly confirmed evidence that lifestyle or everyday exposures meaningfully change the chance of having this condition.
Inheritance of PYGL variants
PYGL-related glycogen storage disease type VI is inherited in an autosomal recessive pattern. This means a child usually needs to inherit one PYGL gene variant from each parent to have the condition, while parents with one variant are typically carriers. When both parents are carriers, each pregnancy has a 25% chance of an affected child, a 50% chance of a carrier child, and a 25% chance of a child with no inherited variant. In practical terms, how PYGL gene variants are inherited depends on both parents passing on the changed copy.
What does my PYGL result mean for my family?
PYGL-related disease usually runs in families in a recessive way, which means parents can carry the gene change without having symptoms themselves. Brothers and sisters of someone with a PYGL-related condition may also be affected or may be healthy carriers. Other relatives, such as future children and extended family members, may also want to learn whether the change runs in the family.
Genetic information
Genetic testing
How you find out about variants
To find out whether you carry a variant in the PYGL gene, doctors use PYGL genetic testing, usually on a blood or saliva sample. The lab reads the DNA code in this gene and compares it with the usual sequence to identify variants that may help confirm glycogen storage disease type VI.
When should I consider getting a genetic test?
Genetic testing for the PYGL gene may be worth considering if someone has signs of a rare liver glycogen storage condition, such as an enlarged liver, low blood sugar between meals, slow growth, or ongoing high liver blood tests. It can also help when this condition runs in the family or when a child may be a carrier.
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 type of variant involved. Over time, many factors, including lifestyle, environment, age, and medical history, influence how the body works. For some conditions, especially those affected by many genes, genetic information adds context rather than certainty and is best understood along with other parts of care. In other situations, a genetic result may offer a clear answer. In areas like 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 because it can change how the body takes in, breaks down, moves, or responds to a drug. This helps explain why the same treatment may work well for one person, seem less effective for another, or cause more side effects in someone else. These differences are common and can influence both how well a medicine works and how sensitive a person is to it.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in a person’s genes can affect their response to medications. By studying the relationship between genes and drugs, it helps explain why the same treatment may work differently from one person to another. For many medicines, genes influence both how strongly a drug works and how the body processes it. This information can help support more informed, more individualized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the PYGL gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medicine choice or dose, so general questions about symptoms, treatment, or side effects are best discussed with your doctor or pharmacist.
History
PYGL entered medical history through studies of a rare inherited condition now called glycogen storage disease type VI, or Hers disease. In 1959, Henri-Gery Hers linked this condition to a lack of liver glycogen phosphorylase activity, giving doctors one of the earliest clear examples of an inborn problem in glycogen breakdown. Initially understood only through visible traits, later recognized as tied to a specific gene, this work helped connect biochemistry with inherited liver conditions. From these first observations, research expanded steadily. As gene mapping and DNA testing improved in the late 20th century, scientists identified the PYGL gene as the cause in affected families. That step made diagnosis more precise and clarified that people with similar symptoms could have different genetic causes.