National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Hartnup disease



Hartnup disease is a metabolic disorder characterized by abnormal transport of certain amino acids in the kidney and gastrointestinal system. It is a type of aminoaciduria. The condition may be diagnosed based on the results of newborn screening tests. Most people with the condition have no symptoms (asymptomatic). For those who do show symptoms, the onset of the disease is usually between the ages of 3 and 9; occasionally the disease may present in adulthood. Mental development is usually normal, though a few cases with intellectual impairment have been reported. The signs and symptoms of Hartnup disease incude skin photosensitivity, neurologic findings, psychiatric symptoms, and ocular (eye) findings. Hartnup disease is caused by mutations in the SLC6A19 gene and is inherited in an autosomal recessive manner.[1][2] People with Hartnup disease may benefit from a high-protein diet, protection from sunlight, vitamin supplementation, and avoidance of certain drugs/medications. In some cases, treatment with nicotinamide supplements and tryptophan ethyl ester may be indicated. [1][2]
Last updated: 12/17/2015

The signs and symptoms of Hartnup disease may vary and include the following:

• Skin findings: sensitivity to sunlight
• Neurologic symptoms: ataxia, spasticity, headaches,and hypotonia
• Psychiatric symptoms: anxiety, emotional instability, mood changes
• Ocular findings: double vision, nystagmus, strabismus, photophobia

Symptoms may be triggered by sunlight exposure, fever, drugs, and emotional or physical stress. The episodes of skin and neurologic findings may last for 1-4 weeks before spontaneous remission occurs.[1][2]
Last updated: 12/17/2015

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Showing of 30 |
Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Abnormal urinary color
Abnormal urinary colour
Abnormal urine color
[ more ]
0012086
Anxiety
Excessive, persistent worry and fear
0000739
Ataxia 0001251
Cutaneous photosensitivity
Photosensitive skin
Photosensitive skin rashes
Photosensitivity
Sensitivity to sunlight
Skin photosensitivity
Sun sensitivity
[ more ]
0000992
EEG abnormality 0002353
Emotional lability
Emotional instability
0000712
Hallucinations
Hallucination
Sensory hallucination
[ more ]
0000738
Hyperreflexia
Increased reflexes
0001347
Migraine
Intermittent migraine headaches
Migraine headache
Migraine headaches
[ more ]
0002076
Muscular hypotonia
Low or weak muscle tone
0001252
Neutral hyperaminoaciduria 0008353
30%-79% of people have these symptoms
Malabsorption
Intestinal malabsorption
0002024
Nystagmus
Involuntary, rapid, rhythmic eye movements
0000639
Photophobia
Extreme sensitivity of the eyes to light
Light hypersensitivity
[ more ]
0000613
Skin rash 0000988
Strabismus
Cross-eyed
Squint
Squint eyes
[ more ]
0000486
5%-29% of people have these symptoms
Abnormal blistering of the skin
Blistering, generalized
Blisters
[ more ]
0008066
Encephalitis
Brain inflammation
0002383
Gingivitis
Inflamed gums
Red and swollen gums
[ more ]
0000230
Global developmental delay 0001263
Glossitis
Inflammation of the tongue
Smooth swollen tongue
[ more ]
0000206
Hypopigmented skin patches
Patchy loss of skin color
0001053
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ]
0001249
Irregular hyperpigmentation 0007400
Seizure 0001250
Short stature
Decreased body height
Small stature
[ more ]
0004322
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance 0000007
Episodic ataxia 0002131
Hypertonia 0001276
Psychosis 0000709
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Last updated: 7/1/2020

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources


Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.

Conditions with similar signs and symptoms from Orphanet
Pellagra is the main differential diagnosis. Blue diaper syndrome, ataxia-telangiectasia, hydroa vacciniforme, pityriasis alba, and xeroderma pigmentosum should be excluded.
Visit the Orphanet disease page for more information.

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease


These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

In-Depth Information

  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Hartnup disease. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.


  1. Sekulovic, Lidija Kandolf. Hartnup Disease. Medscape Reference. October 8, 2015; http://emedicine.medscape.com/article/1115549-overview. Accessed 12/17/2015.
  2. Wendel, Udo. Hartnup Disease. Orphanet. April, 2014; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=2116. Accessed 12/17/2015.