Hartnup Disease: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats Hartnup Disease?
A geneticist, a doctor who treats inherited conditions, often guides care for Hartnup disease. A metabolic specialist, a doctor who treats how the body handles nutrients, may also help. Most people have no symptoms at all. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is Hartnup disease?
Hartnup disease is a condition in which the body cannot absorb certain amino acids from food. Amino acids are the building blocks of protein. The condition is also called Hartnup disorder.
Most people with Hartnup disease can get the vitamins they need from a well-balanced diet. It is estimated to affect 1 in 30,000 people. It affects males and females in equal numbers.
Symptoms
Most people with Hartnup disease have no symptoms. For most, the only sign is a high level of amino acids in the urine.
Some people have episodes with other signs. These can include:
- A red, scaly skin rash, usually where the skin is exposed to sunlight.
- Trouble coordinating movements, called cerebellar ataxia.
- Mood changes, depression, or other psychiatric symptoms.
- Diarrhea, sensitivity to light, and short stature.
These episodes are usually temporary. They are often triggered by illness, stress, a poor diet, or fever. The features tend to go away once the trigger is gone. The amino acids in the urine stay high.
Symptoms most often appear in childhood, between ages 3 and 9. In rare cases they first appear in adulthood.
Causes and who gets it
Hartnup disease is caused by changes in the SLC6A19 gene. This gene makes a protein that moves certain amino acids into cells in the intestines and kidneys. When the protein works poorly, the amino acids are lost in the urine. The body cannot use them.
One of these amino acids is tryptophan. The body needs it to make vitamin B3, also called niacin. Researchers believe a shortage of tryptophan and niacin causes many of the symptoms.
The condition is inherited in an autosomal recessive pattern. This means a child gets a changed gene from both parents. Each parent carries one changed gene. The parents typically do not have symptoms.
How doctors diagnose it
A doctor will order a urine test to look for high levels of neutral amino acids. Your doctor can also test for the gene that causes the condition. Gene testing can confirm the diagnosis in some people. It is usually not needed.
Treatment
People who have no symptoms usually do not need treatment. For others, treatment can include:
- Eating a high-protein diet.
- Avoiding too much sun by wearing protective clothing and using sunscreen.
- Taking supplements that contain nicotinamide, a form of vitamin B3. Niacin may also help prevent episodes.
- Avoiding certain drugs, such as sulphonamide drugs.
- Mental health treatment, such as antidepressants or mood stabilizers, if mood swings or other mental health problems occur.
Genetic counseling is recommended for affected families. Most people with this disorder can expect to live a normal life with no disability.
When to see a doctor
Contact your doctor if you have symptoms of this condition. This matters most if Hartnup disease runs in your family. If you plan a pregnancy and have a personal or family history, genetic counseling is recommended.
In rare cases, nervous system symptoms can be severe or life threatening. Call 911 or go to the emergency room if you or someone with this condition faints, has a sudden change in mental state, or has trouble breathing.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Either type of doctor can do an evaluation, order tests, and keep track of your health over time. They can also help you find a geneticist when needed.
Common questions
Is Hartnup disease serious?
No, not for most people. Most people with this disorder can expect to live a normal life with no disability. Rarely, there have been reports of severe nervous system disease and even deaths in families with this disorder.
Can Hartnup disease be prevented?
Some cases may be prevented. Genetic counseling before marriage and conception may help prevent some cases. Eating a high-protein diet may prevent the amino acid shortages that cause symptoms.
What triggers symptoms of Hartnup disease?
Illness, stress, a poor diet, and fever can trigger episodes. Exposure to sunlight and sulphonamide medicines can also bring on an episode. The shortage of tryptophan is most harmful during times of illness or stress.
Does everyone with Hartnup disease need treatment?
No. People who have no symptoms usually do not need treatment. Treatment is mainly for people who have episodes. It focuses on diet, sun protection, and nicotinamide or niacin.
Sources
- MedlinePlus - Hartnup disease (MedlinePlus Genetics)
- National Organization for Rare Disorders (NORD) - Hartnup Disease
- MedlinePlus - Hartnup disorder
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
