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What

Hartnup disease is a rare, inherited condition where the body cannot absorb certain amino acids, especially tryptophan. This defect is in the small intestine and in the kidneys. amino acids are the building blocks of proteins. The body needs tryptophan in order to make niacin (vitamin B3). Hartnup disease was first described in 1956 in the Hartnup family of London.

Who

Approximately one in 25,000 children have Hartnup disease. Girls and boys of all races and ethnicities are affected equally.

Signs and Symptoms

Eighty percent of children with Hartnup disease never develop symptoms. In the remaining 20%, symptoms typically begin between 3-9 years of age, but can occur as early as 10 days after birth. A skin rash develops before neurologic problems. Attacks usually start with diarrhea and occur in the spring or early summer. Attacks are triggered by a low protein diet, sunlight, fever, illness, poor nutrition, or emotional stress. A dry, red and scaly rash resembling eczema develops on the forehead and cheeks, around the mouth, on the backs of the hands, and on other sun-exposed areas. Weeping of the skin may occur. After the rash resolves, the skin may be lightened or darkened. Neurologic abnormalities include difficulty walking (ataxia), headache, fainting spells, muscle rigidity (or stiffness), double vision, jerky-eye movements, difficulty looking at light, and eye-crossing. Some patients may develop mild mental retardation. Psychiatric symptoms include anxiety, emotional instability, mood changes, confusion, and agitation. Other symptoms of niacin deficiency include gingivitis and oral and tongue ulcers. A few patients may have short stature.

Possible Causes

Hartnup disease is inherited in an autosomal recessive manner. This means that two mutated genes are necessary to have this disorder. The parents of the affected child are usually healthy, but each carries a copy of the mutated gene. When both parents are carriers, there is a 25% chance of each of their children developing this disease. There is a 67% chance that unaffected children will be carriers. Hartnup disease is not contagious or preventable. Hartnup disease is caused by a change in a gene called “Solute carrier Family 6” (SLC6A19), which is located on chromosome 5. This gene normally makes a protein found in the intestines and the kidneys. This protein is needed to absorb certain amino acids from foods in our diet, including tryptophan. When the body cannot absorb tryptophan, niacin deficiency develops. Also, since the body cannot absorb amino acids, the amino acids are lost in the urine and stool. Without this protein, amino acids also accumulate abnormally in the intestine. bacteria in the gut then change them to compounds that are toxic to the brain.

Diagnosis

A special urine test that detects amino acids can be used to diagnose Hartnup disease. Blood tests of amino acids are usually normal. A biopsy of the intestine and/or skin may be required to confirm the diagnosis in some patients. Prenatal testing is available.

Treatment

The symptoms of Hartnup disease are reversible with treatment. A high protein diet can supply the body with sufficient amounts of niacin. Daily niacin supplements reduce the number and severity of attacks. Sun exposure should be minimized. Sunscreen is highly recommended. Sulfa drugs should be avoided as these increase the skin’s sensitivity to sunlight. If severe neurologic or psychiatric conditions present, special medications may be necessary.

Prognosis

With treatment, prognosis is very good. Attacks become less frequent with age.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

CLIMB (Children Living with Inherited Metabolic Diseases)
National organization providing information, news, financial support and networking.

Worldwide Education and Awareness for Movement Disorders
National organization for those affected with ataxia providing education, information about research, and support.

e-medicine
A very comprehensive article with complex material.

Google Search for Hartnup Disease

References and Sources

The Arc (a national organization on mental retardation) www.thearc.org/ A national organization providing education, support and advocacy. www.emedicine.com/derm/topic713.htm