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PubMed This is a summary of 24 peer-reviewed journal articles Updated
Genetics

Understanding Hartnup Disease

At a Glance

Hartnup disease is a rare genetic condition affecting amino acid absorption, which can cause niacin deficiency. Symptoms like sun-sensitive rashes and unsteadiness are effectively treated with a high-protein diet, sun protection, and niacin supplements.

Receiving a diagnosis of Hartnup disease can feel overwhelming, but it is important to know that for many people, this condition is manageable and often does not interfere with a full, healthy life [1][2]. While it is a lifelong genetic condition, understanding how it works is the first step toward taking control of your or your child’s health.

What is Hartnup Disease?

Hartnup disease is a rare autosomal recessive metabolic disorder, meaning a person must inherit two copies of a specific mutated gene (one from each parent) to have the condition [3][4]. It is caused by mutations in the SLC6A19 gene, which provides instructions for a “transporter” protein in the kidneys and intestines [3][5].

In a healthy body, this transporter helps absorb neutral amino acids—the building blocks of protein—from food and prevents them from being lost in the urine [5][6]. In Hartnup disease, this transporter does not work correctly. One of the most important building blocks affected is tryptophan, which the body normally uses to create niacin (Vitamin B3) [2][7]. Without enough tryptophan absorption, a person can develop a niacin deficiency [2].

For a deeper dive into the science, read about The Biology and Genetics of Hartnup Disease.

Three Stabilizing Facts

  1. Many people have no symptoms: Many individuals with the genetic markers for Hartnup disease lead completely normal lives and are only diagnosed through routine screening or testing for other issues [8][1].
  2. It is highly treatable: Most symptoms can be prevented or quickly reversed with simple nutritional changes, specifically a high-protein diet and niacin supplements [9][10].
  3. It is not a “progressive” disease: Unlike some genetic conditions that get worse over time regardless of care, Hartnup symptoms are usually triggered by specific events like poor nutrition, illness, or sun exposure, and can be stabilized with proper management [2][9].

The Patient Journey: From Diagnosis to Daily Life

The path to diagnosis often begins when a doctor notices a photosensitive rash (a red, scaly rash that appears on skin exposed to the sun) or neurological symptoms like ataxia (unsteadiness or lack of coordination) [2][7]. Learn more about Symptoms and Triggers.

01

How Hartnup Disease is Diagnosed

Learn how Hartnup disease is diagnosed through urine amino acid analysis and genetic testing. Understand the HAA/OAA ratio and what lab results mean.

02

Treating and Living with Hartnup Disease

Learn how to manage Hartnup disease with nicotinamide supplements, a high-protein diet, and sun protection. Discover strategies for preventing flare-ups.

Outlook and Quality of Life

The vast majority of patients with Hartnup disease have an excellent prognosis [1]. While severe or untreated cases can lead to neurological challenges, most children reach their developmental milestones and live normal adult lives with simple dietary adjustments [9][8].

Common questions in this guide

What are the first signs of Hartnup disease?
The most common initial signs include a red, scaly rash that appears on skin exposed to the sun. Some individuals may also develop neurological symptoms like unsteadiness, poor coordination, or mood swings.
How is Hartnup disease diagnosed?
Doctors typically diagnose this condition by analyzing a urine sample. They look for abnormally high levels of specific amino acids, a medical finding known as neutral aminoaciduria.
Can Hartnup disease be cured?
While it is a lifelong genetic disorder that cannot be cured, it is highly treatable. Most symptoms can be completely prevented or reversed through simple lifestyle changes, such as a high-protein diet and specific vitamin supplements.
Does everyone with Hartnup disease experience symptoms?
No, many people who carry the genetic markers for Hartnup disease never develop symptoms. These individuals often lead completely normal, healthy lives and may only learn they have the condition during routine screening.
Why do people with Hartnup disease need to take niacin supplements?
Hartnup disease limits the body's ability to properly absorb tryptophan, an amino acid normally used to produce niacin (Vitamin B3). Taking niacin or nicotinamide supplements helps prevent a deficiency and resolves many associated symptoms.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.How do you determine if my child is asymptomatic or needs immediate treatment?
  2. 2.What target dose of nicotinamide is appropriate for my child's weight?
  3. 3.Can you refer us to a pediatric metabolic dietitian who has experience with protein management?
  4. 4.How often should we repeat the urine amino acid tests to monitor the condition?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (10)
  1. 1

    Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency.

    Belanger AJ, Gefteas E, Przybylska M, et al.

    Journal of inherited metabolic disease 2023; (46(1)):55-65 doi:10.1002/jimd.12568.

    PMID: 36220785
  2. 2

    New aspects for the brain in Hartnup disease based on mining of high-resolution cellular mRNA expression data for SLC6A19.

    Kravetz Z, Schmidt-Kastner R

    IBRO neuroscience reports 2023; (14()):393-397 doi:10.1016/j.ibneur.2023.03.010.

    PMID: 37101820
  3. 3

    Accurate discrimination of Hartnup disorder from other aminoacidurias using a diagnostic ratio.

    Haijes HA, Prinsen HCMT, de Sain-van der Velden MGM, et al.

    Molecular genetics and metabolism reports 2020; (22()):100551 doi:10.1016/j.ymgmr.2019.100551.

    PMID: 31908951
  4. 4

    Hartnup disease-causing SLC6A19 mutations lead to B0AT1 aberrant trafficking and ACE2 mis-localisation implicating the endoplasmic reticulum protein quality control.

    Alkhofash NF, Ali BR

    Frontiers in cell and developmental biology 2025; (13()):1589534 doi:10.3389/fcell.2025.1589534.

    PMID: 40852587
  5. 5

    Study of Seizure-Manifested Hartnup Disorder Case Induced By Novel Mutations in SLC6A19.

    Zhu Y, Chen L, He J, et al.

    Open life sciences 2018; (13()):22-27 doi:10.1515/biol-2018-0003.

    PMID: 33817063
  6. 6

    In vivo antidiabetic activity of nimesulide due to inhibition of amino acid transport.

    Joharapurkar A, Kshirsagar S, Patel V, et al.

    Basic & clinical pharmacology & toxicology 2022; (130(1)):35-43 doi:10.1111/bcpt.13670.

    PMID: 34634192
  7. 7

    ACE2 and gut amino acid transport.

    Camargo SMR, Vuille-Dit-Bille RN, Meier CF, Verrey F

    Clinical science (London, England : 1979) 2020; (134(21)):2823-2833 doi:10.1042/CS20200477.

    PMID: 33140827
  8. 8

    Hartnup disease presenting as hereditary spastic paraplegia and severe peripheral neuropathy.

    Wang X, Li XY, Piao Y, et al.

    American journal of medical genetics. Part A 2022; (188(1)):237-242 doi:10.1002/ajmg.a.62475.

    PMID: 34459558
  9. 9

    Adult Neuropsychiatric Manifestation of Hartnup Disease With a Novel SLCA6A19 Variant: A Case Report.

    Bachmann T, Faust H, Abou Jamra R, et al.

    Neurology. Genetics 2024; (10(6)):e200195 doi:10.1212/NXG.0000000000200195.

    PMID: 39611136
  10. 10

    Loss of CLTRN function produces a neuropsychiatric disorder and a biochemical phenotype that mimics Hartnup disease.

    Pillai NR, Yubero D, Shayota BJ, et al.

    American journal of medical genetics. Part A 2019; (179(12)):2459-2468 doi:10.1002/ajmg.a.61357.

    PMID: 31520464

This page is for informational purposes only and does not replace professional medical advice. Always consult a healthcare provider or pediatric metabolic dietitian regarding the management of Hartnup disease for you or your child.

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