What is Hartnup disease?
Hartnup disease is also referred to as Hartnup disorder.
It’s a hereditary metabolic disorder. It makes it difficult for your body to
absorb certain amino acids from your intestine and reabsorb them from your kidneys.
Amino acids are essential building blocks for creating protein in your body.
Hartnup disease was named for the Hartnup family of England,
who were featured in a 1956 study of the condition. Four out of eight family
members were found to have excessive amounts of amino acids in their urine.
They also had skin rash and a lack of coordination of their voluntary muscle
movements, known as ataxia. These are the signs and symptoms characteristic of
Hartnup disease, which typically affects the skin and brain.
Organization for Rare Disorders reports that Hartnup disease is estimated
to affect about one in 30,000 people in the United States. Symptoms normally start
to appear in infancy or the first few years of life. Symptoms last for about
two weeks when there is an “attack.” The frequency of these attacks decreases with
What are the symptoms of Hartnup disease?
Your brain and skin remain healthy and function properly if
you get the required amount of vitamin B complex. If you have Hartnup disease,
you can’t absorb certain amino acids properly. This impedes your body’s ability
to produce protein and to make vitamin B complex. It can trigger specific
mental and physical symptoms, including:
wide-based gait, in which you walk with your legs farther apart than normal
in muscle tone, in which your muscles become tighter or lose tone
A skin rash called “pellagra” is a common symptom. It
usually results from exposure to sunlight. It’s an intermittent red and scaly
rash that typically appears over your face, neck, hands, and legs. It’s
initially red, but over time it can progress to an eczematous-like rash. With
prolonged sun exposure, the changes in your skin pigmentation can become
Sunlight, poor nutrition, sulfonamide drugs, or emotional or
physical stress may trigger symptoms.
Although symptoms usually begin to appear in infancy or
early childhood, they may also appear in early adulthood. Acute attacks of symptoms
generally become less frequent as you get older.
What causes Hartnup disease?
Hartnup disease is caused by a mutation of the gene that
controls your body’s amino acid absorption and reabsorption. It’s an autosomal
recessive trait. That means that people who are born with the condition have
inherited a mutated gene from both parents. Scientists aren’t sure why the
In most people, your body absorbs specific amino acids into your
intestines and then reabsorbs them in your kidneys. If you have Hartnup
disease, you can’t properly absorb certain amino acids from your small intestine.
You also can’t reabsorb them from your kidneys. As a result, an excessive
amount of amino acids exits your body through urination. This leaves your body
with an insufficient amount of these amino acids.
Among other amino acids, Hartnup disease affects your
ability to absorb tryptophan. This is an important building block for proteins
and vitamins. Without enough tryptophan, your body can’t produce enough niacin.
A niacin deficiency can cause you to develop a sun-sensitive rash. It can also
lead to dementia.
is Hartnup disease diagnosed?
If your doctor suspects you have Hartnup disease, they may
order a urinalysis test. They will collect a sample of your urine to send to a
laboratory to measure the amount of amino acids excreted through your urine. If
there are high levels of “neutral” amino acids in your urine, it may be a sign
of Hartnup disease.
This test alone isn’t enough to diagnose Hartnup disease.
Your doctor will also review your personal and family medical history. They
will ask you about your symptoms, how frequently you have them, and when they
first began. They may also order a blood test to check your levels of vitamin B
complex, including niacin.
How is Hartnup disease treated?
If you’re diagnosed with Hartnup disease, your doctor will likely
advise you to change your diet, avoid sunlight, and avoid sulfonamide drugs.
Since those with Hartnup disease can’t produce enough
niacin, consuming foods that contain niacin can significantly reduce your
symptoms. Good sources of niacin include:
Red meat, poultry, fish, and peanuts are also excellent
sources of protein. Choose lean cuts of red meat and skinless poultry. The fat
and skin of meat and poultry are rich sources of saturated fat. Eating too much
saturated fat can raise your risk of high cholesterol.
Your doctor may also suggest taking vitamin B complex or
niacin supplements, such as nicatonic acid. Your recommended supplement dosage
will depend on the severity of your niacin deficiency.
Your doctor may also advise you to avoid direct exposure to
the sun. For example, they may encourage you to wear sunscreen and protective
What is the long-term outlook
for Hartnup disease?
In most cases, people with Hartnup disease can live healthy
lives. Complications of the condition are rare. But it’s possible to undergo
changes in skin pigmentation, have trouble coordinating your physical
movements, or develop psychiatric problems as a result of this condition. In
rare cases, you may develop diseases of your nervous system.
Nervous system conditions can be life threatening, but in
most cases your doctor can treat them effectively. Ask your doctor for
strategies to manage your condition and lower your risk of complications.