What is Hartnup Disease?

Hartnup disease is an autosomal recessive (AR) disease, which is characterized by skin lesions similar to pellagra (characteristic skin manifestations due to deficiency of niacin, a B-complex vitamin), variable neurological manifestations, and neutral and aromatic aminoaciduria (excretion of amino acids in urine). In Hartnup disease excretion of several amino acids (alanine, asparagines, serine, threonine, leucine, isoleucine, glutamine, histidine, phenylalanine, tryptophan, tyrosine, and valine) is 5-10 times more than normal individuals. The amino acids are excreted due to defect in neutral amino acid transporter, due to defect in the SLC6A19 gene on chromosome 5p15. Intestinal transport and renal tubular reabsorption of these amino acids are defective.

How common is Hartnup disease?

The global incidence/prevalence of Hartnup disease is 1 in 24,000 people.

What are the symptoms of Hartnup disease?

The clinical manifestations (symptoms) of Hartnup disease include pellagra like skin problems, neurologic and psychiatric manifestations range from attacks of cerebellar ataxia to mild emotional lability to frank delirium. The symptoms are usually having exacerbations of the erythematous, eczematoid skin rash. The symptoms may relapse due to fever, sunlight, stress, and sulfonamide therapy.

The symptoms (pellagra like skin problems, neurologic and psychiatric manifestations etc.) are due to deficiency of essential amino acid tryptophan, which is due to defect in renal reabsorption and defect in intestinal transport. Due to deficiency of tryptophan, niacin deficiency develops, which is partly synthesized from tryptophan (1 mg of niacin is synthesized from 60 mg of tryptophan).

Diagnosis of Hartnup disease:

Diagnosis of Hartnup disease should be suspected if any patient presents with pellagra like symptoms without any history of dietary niacin deficiency. The diagnosis is based on detection of the neutral amino acids in urine, which is not seen in case of niacin deficiency and pellagra.

Treatment of Hartnup disease:

Treatment of Hrtnup disease is supplementation of niacin (to correct niacin deficiency and prevent symptoms due to niacin deficiency) and intake of high protein diet, with supplementation of 50-250 mg nicotinamide per day.

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