Hartnup Disease: Symptoms, Causes, Diagnosis & Treatment

Written by Medicover Team and Medically Reviewed by Dr Marwa Rafique Deshmukh , Dermatologists

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1. Causes 2. Find a Doctor 3. Diagnosis 4. Treatment 5. FAQs

Hartnup disease is a rare inherited metabolic disorder caused by impaired absorption of certain amino acids, particularly tryptophan, in the intestines and kidneys. It may lead to skin rashes, neurological symptoms, mood changes, and growth problems, especially during illness or poor nutrition. Early diagnosis and appropriate treatment, including dietary management and vitamin supplementation, help prevent complications and improve quality of life.

What Are the Common Symptoms of Hartnup Disease?

The symptoms of Hartnup disease can vary widely among individuals, with some experiencing mild symptoms and others facing more severe complications. The most common symptoms include:

Dermatological Symptoms

Photosensitivity: Patients often develop a red, scaly rash after exposure to sunlight, particularly on areas of the skin that are not usually covered by clothing.
Erythema: This refers to the reddening of the skin, which can be temporary or persistent, often exacerbated by sun exposure.

Neurological Symptoms

Ataxia: This is a lack of voluntary coordination of muscle movements, which can affect gait and balance.
Tremors and Unsteady Gait: Some patients may experience tremors or an unsteady walk, often attributed to the central nervous system's involvement.

Gastrointestinal Symptoms

Diarrhoea: Due to amino acid malabsorption, gastrointestinal disease disturbances like diarrhoea can occur.

Psychiatric Symptoms

Mood Swings and Anxiety: Changes in mood and increased anxiety levels are noted in some patients, likely due to serotonin syndrome and niacin deficiencies.

Hartnup Disease and Amino Acids

The inability to properly transport and absorb neutral amino acids, such as tryptophan, leads to their increased excretion in urine. Since tryptophan is a precursor for the synthesis of nicotinamide (a form of niacin), its deficiency can mimic symptoms of pellagra, a condition caused by niacin deficiency.

What Are the Causes of Hartnup Disease?

Hartnup disease is caused by inherited genetic mutations that impair the transport of neutral amino acids, leading to reduced absorption and increased urinary loss.

Mutations in the SLC6A19 gene
Autosomal recessive inheritance
Defective transport of neutral amino acids
Tryptophan deficiency leading to reduced niacin production
Symptoms triggered by poor nutrition, illness, stress, or excessive sun exposure

When to See a Doctor for Hartnup Disease?

Consult a metabolic specialist, dermatologists, or pediatrician if you or your child develops recurrent sun-sensitive rashes, coordination problems, unexplained neurological symptoms, or has a family history of Hartnup disease. Early diagnosis and treatment can help prevent long-term complications.

You should see a doctor if you have:

Recurring skin rash after sun exposure
Poor coordination or balance problems
Persistent diarrhea with nutritional concerns
Behavioral or mood changes with unexplained neurological symptoms

Get medical help immediately if:

Severe confusion or altered consciousness
Seizures
Severe dehydration due to persistent diarrhea
Sudden worsening of neurological symptoms

These could indicate serious complications requiring urgent medical care.

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How is Hartnup Disease Diagnosed?

Diagnosing Hartnup disease involves a combination of clinical evaluation, family history, and laboratory tests. The hallmark diagnostic feature is the presence of elevated levels of neutral amino acids in the urine, detected through a urine amino acid chromatography test.

Genetic Testing

Genetic testing can confirm the diagnosis by identifying mutations in the SLC6A19 gene. This is particularly useful for family planning and understanding the genetic implications for future offspring.

What are the Treatment Options for Hartnup Disease?

Treatment for Hartnup disease is generally symptomatic and supportive. The primary goals are to manage symptoms and prevent complications.

Dietary Management

High-Protein Diet: Since amino acids are the building blocks of proteins, a high-protein diet can help mitigate the effects of amino acid malabsorption.
Niacin or Nicotinamide Supplements: Supplementation helps to prevent pellagra-like symptoms by compensating for the reduced synthesis of niacin from tryptophan.

Sun Protection

Use of Sunscreen: Regular application of broad-spectrum sunscreen can help prevent skin rashes and other photosensitivity-related issues.
Protective Clothing: Wearing long sleeves and hats can further reduce sun exposure and to avoid skin manifestations.

Symptomatic Treatment

Anticonvulsants and Psychiatric Medications: In cases of severe neurological or psychiatric symptoms, medications may be prescribed to manage these conditions effectively.

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