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.
The National 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 age.
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:
- skin rash
- rapid mood swings
- intention tremor
- speech difficulties
- unsteady wide-based gait, in which you walk with your legs farther apart than normal
- abnormalities in muscle tone, in which your muscles become tighter or lose tone
- short stature
- sensitivity to light
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 permanent.
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.
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 mutation occurs.
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.
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.
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
- peanut butter
- fortified grains
- whole grains
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 clothing.
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.