Key points
- Kallmann syndrome is a genetic condition where the body does not make enough sex hormones.
- If left untreated, your child will not start puberty and will not be able to have children.
- Kallmann syndrome also affects the sense of smell.
- People with Kallmann syndrome need long-term treatment with hormone medicines so they can grow and develop normally, and to enable them to have children in the future.
What is Kallmann syndrome?
Kallmann syndrome is a condition where the body does not make enough of a hormone called gonadotropin-releasing hormone (GnRH). The role of GnRH is to stimulate the testicles in males and the ovaries in females, to make sex hormones. If not enough of these hormones are made, the child will not enter puberty and will not be able to have children of their own without special treatment.
People with Kallmann syndrome need long-term treatment with hormone replacement medicines. It is generally effective.
Kallmann syndrome is also known as hypothalamic hypogonadism, familial hypogonadism with anosmia, or hypogonadotropic hypogonadism.
What causes Kallmann syndrome?
Kallmann syndrome is a genetic condition. It can be passed from parents to their children in a variety of ways – the most common being linked to the X chromosome. Less commonly, the syndrome can be passed in either an autosomal dominant (one copy of the faulty gene) or recessive (two copies of the faulty gene) manner. Rarely, the gene change that causes Kallmann syndrome can happen for the first time in the affected person without any prior family history.
Signs and symptoms of Kallmann syndrome
Children with Kallman syndrome will often have a very poor or no sense of smell from birth. This cannot be treated.
- Boys can have a small penis and experience delayed puberty
- Girls have a delay in breast and pubic hair development, and no menstruation (monthly period)
- If not treated, both boys and girls will be infertile (not able to have children).
Sometimes, Kallmann syndrome can also affect the kidneys, ears, heart, eyes and parts of the brain. Some children with Kallmann syndrome will have a cleft palate, obesity, problems with sight or hearing, or an intellectual disability. However, not everyone with Kallmann syndrome has any or all of these extra problems.
When to see a doctor
If your child has not started showing signs of puberty around the same time as their peers and you are worried, speak with their doctor. This is especially important if your child also has a history of reduced or absent smell or taste. The smell of food is part of how we taste, so not being able to smell properly means some children may find unusual food combinations appetising.
Testing for Kallmann syndrome
Your child may be referred to a paediatrician (doctor who specialises in medicine for children under 18) or a paediatric endocrinologist (doctor who specialises in hormones for children under 18). Kallmann syndrome is usually diagnosed after several tests that explore why the growth spurt that usually comes with puberty is late.
It is normal for sex hormones to be low in children, so your child may need to have something called a ‘stimulation test.’ This is where a health professional injects your child with the GnRH hormone and then measures their levels of sex hormones. If the sex hormone levels stay low, this is a sign of Kallmann syndrome.
Treatment for Kallmann syndrome
Hormone replacement is given to both boys and girls with Kallmann syndrome. Boys need a hormone called testosterone, which lets them grow and develop during puberty. Girls need the female sex hormones, oestrogen and progesterone. If they wish to have children, both boys and girls also need other hormones so their bodies can make sperm and eggs.
Hormone replacement is a long-term treatment. The type of hormone and how it is given depend on what works best for your child at different ages. Sometimes, the hormones are given as tablets; other times, they are given as injections.
As well as helping with development during puberty, these hormones are essential for your child's body to lay a good foundation for bone strength and to reduce the risk of osteoporosis (weak bones) in later life.
There is no treatment for the lack of a sense of smell.
Ongoing care
After receiving a Kallmann syndrome diagnosis, your child should have regular appointments with an endocrinologist and continue these appointments as an adult. If other parts of their body are affected, such as their kidneys or heart, then they will need care from other health professionals, too.
Common questions about Kallman syndrome
Is there any cure for Kallmann syndrome?
There is not yet a cure for Kallman syndrome. Finding cures for genetic (inherited) disorders is very difficult, and research into life-threatening conditions is generally prioritised. Treatment is usually very effective for Kallmann syndrome, with few side effects.
What should I do if my child has no sense of smell?
Unfortunately, there is no way to treat a lack of sense of smell. Not being able to smell properly or at all can be dangerous, as your child will not be able to smell smoke or know when food has gone off. It is important to teach them other ways to stay safe in these areas. For example, learning other ways to assess the freshness of food and visual signs that it may not be safe to eat. You should also make sure to check smoke detectors and change batteries regularly.
Developed by The Royal Children's Hospital Endocrinology department. We acknowledge the input of RCH consumers and carers.
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Reviewed November 2025
Please always seek the most recent advice from a registered and practising clinician.