The IGSF1 gene helps the pituitary gland send hormone signals that support thyroid function, growth, puberty, and milk production after childbirth. If it does not work properly, the brain may send weaker signals to the thyroid, leading to low thyroid activity, tiredness, slow growth, weight gain, or feeling unusually cold. Some boys and men with variants in the IGSF1 gene also have larger testes, a later rise in testosterone, or low prolactin. Because this gene is on the X chromosome, its effects are often more noticeable in males.
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 provide the directions for making proteins, the parts of cells that do much of the work. Other genes mostly control when certain processes happen, where they happen, and how strongly they occur. Together, genes influence how the body develops and functions, and they can affect how you respond to food, stress, or medications. To explore this topic in more detail, you can learn more in the LearnHub.
Overview
IGSF1Gene function
What if the gene works
The IGSF1 gene helps the pituitary gland release signals that support normal thyroid hormone control, growth, and puberty. It is most active in the brain areas that coordinate hormone production.
Risk
What if the gene does not work
Variants in the IGSF1 gene can cause central hypothyroidism, often with delayed puberty and enlarged testes, and some people also have low prolactin or growth hormone. Milder and severe variants can influence which features appear and how noticeable they are.
Treatment
What does that mean for your treatment
No IGSF1-specific treatment or drug choice is currently established. Care is guided by the hormone changes a person has, with standard endocrine treatment such as thyroid hormone replacement when central hypothyroidism is present.
Conditions associated with IGSF1
Gene function
What if the gene works
In the pituitary gland, a small gland at the base of the brain, the IGSF1 gene supports normal hormone control. It makes a protein that sits on the surface of certain pituitary cells and helps them handle hormone signals in an organized way. This supports the normal production of hormones linked to thyroid function, growth, and prolactin.
Its protein sits on the surface of certain pituitary cells. There, it helps those cells receive and process hormone messages from the brain.
By supporting these messages, the pituitary can make thyroid stimulating hormone, which tells the thyroid when to release thyroid hormone. This is part of how the IGSF1 gene helps the pituitary control thyroid hormone levels.
The IGSF1 gene is also active in pituitary cells involved in growth hormone and prolactin release. When it works properly, these cells can keep hormone production and release well coordinated.
What is a variant?
A genetic variant is a small alteration in the DNA sequence within a gene. These changes are common and help shape normal human diversity, such as differences in appearance, metabolism, or how the body responds to environmental influences. Many variants do not cause any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change how a gene functions more significantly and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the IGSF1 gene often reduce how much IGSF1 protein a cell makes or keep it from folding correctly and reaching the cell surface. Some changes allow partial activity, while more disruptive variants leave little or no working protein. That range helps explain how IGSF1 gene variants affect central hypothyroidism, with some people showing earlier or more noticeable features than others.
How variants are linked to conditions
Pathogenic variants in the IGSF1 gene cause IGSF1 deficiency syndrome, an X-linked condition best known for central hypothyroidism. In many affected boys and men, IGSF1 gene variants linked to central hypothyroidism can also lead to larger than average testes, a delayed rise in testosterone during puberty, and sometimes low prolactin or growth hormone deficiency. Some people also have higher body weight.
A variant is not necessarily a diagnosis
Variants in genes are a routine part of human biology and are widely seen in the general population. Most do not have a direct effect on health and simply 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 several genes and environmental factors are involved. In some situations, though, 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 IGSF1, risk is mostly set by whether a disease-causing variant is inherited, and males are more likely to have clear symptoms while females often have milder changes or none at all. There is not enough evidence to say that lifestyle or environmental factors meaningfully change the chance of developing the condition.
Inheritance of IGSF1 variants
When people look into how IGSF1 gene variants are inherited, the usual pattern is X linked inheritance. Because the IGSF1 gene sits on the X chromosome, a mother carrying a variant can pass it to both sons and daughters. Sons who inherit the variant are more likely to have clear features, while daughters may have milder effects or none. A father with an IGSF1 variant passes it to all daughters and to none of his sons.
What does my IGSF1 result mean for my family?
A result in the IGSF1 gene can matter for close relatives because this condition follows an X-linked pattern. Male relatives on the mother’s side may be more likely to have related hormone problems, while female relatives may carry the gene change and sometimes have milder thyroid changes themselves. Because of this, siblings, children, and other maternal relatives may want to review the result with their care team or a genetic counselor.
Genetic information
Genetic testing
How you find out about variants
IGSF1 genetic testing can show whether you carry a variant linked to IGSF1 deficiency. A lab reads the IGSF1 gene from a blood or saliva sample and may also check whether part of the gene is missing or extra. Results may help clarify an inherited diagnosis and family risk.
When should I consider getting a genetic test?
Genetic testing for the IGSF1 gene can be worth considering when someone, especially a boy or man, has a form of low thyroid hormone caused by weak brain signals (central hypothyroidism), delayed puberty, larger-than-expected testicles, or a family history of these findings. It can help tie these features together.
A genetic result is only one part of your health story
Genetic results can be informative, but how much they can tell you varies based on the condition and the kind of variant involved. Over time, factors such as lifestyle, environment, age, and medical history also affect how the body functions. For some conditions, especially those shaped by many genes, genetic information offers context rather than certainty and is most useful when viewed alongside other parts of care. In other situations, a genetic result may give a clear answer. For medication response, these 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. This happens because inherited differences can change how the body breaks down a drug, moves it through the body, or responds to it at its target. As a result, the same medication may work better for some people, have less effect in others, or cause side effects more easily.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic differences shape the way people respond to medicines. It studies gene and drug patterns to understand why the same treatment can affect one person differently than another. For many drugs, genes influence both how strongly a medicine works and how the body handles it. This information can support more informed and more personalized treatment decisions. More detailed information on this topic is available in the LearnHub.
Drugs influenced by the IGSF1 gene
When should I seek medical advice?
At this time, there is no broadly confirmed role for this gene in guiding how medicines are chosen or used. If you have concerns about side effects, treatment response, or your overall health, discuss them with your doctor, who can look at the full picture.
History
The IGSF1 gene entered medical genetics relatively recently, after doctors noticed families in which boys and men shared a similar pattern of central hypothyroidism and delayed testosterone rise in puberty. In 2012, researchers identified pathogenic variants in the IGSF1 gene as the cause of this X linked condition, now called IGSF1 deficiency syndrome. Initially understood only through visible traits, later recognized as tied to a specific gene, the condition became easier to define and study. From these first observations, research expanded steadily. This work helped connect scattered clinical reports into one clearer diagnosis and improved recognition of affected families.