- Hartnup disease (also known as "pellagra-like dermatosis")
- Autosomal recessive metabolic disorder affecting the absorption of nonpolar amino acids (particularly tryptophan that can be, in turn, converted into serotonin, melatonin, and niacin).
- Niacin is a precursor to nicotinamide, a necessary component of NAD+.
- Inherited as an autosomal recessive trait.
- Heterozygotes are normal.
- Consanguinity is common. .
- Causative gene, SLC6A19
SIGNS & SYMPTOMS:
- Hartnup disease manifests during infancy with variable clinical presentation:
- Failure to thrive,
- Intermittent ataxia,
- Nystagmus, and tremor.
- Increased amounts of amino acids in the urine.
- A rash develops on parts of the body exposed to the sun.
- Mental retardation, short stature, headaches, unsteady gait, and collapsing or fainting are common.
- Psychiatric problems (such as anxiety, rapid mood changes, delusions, and hallucinations) may also result
- Symptoms may be triggered by:
- Drugs, or
- Emotional or physical stress.
- Poor nutrition
- Deficiency of niacinamide.
- In Hartnup disease, urinary excretion of proline, hydroxyproline, and arginine remains unchanged, differentiating it from other causes of generalized aminoaciduria, such as Fanconi syndrome.
- With urine chromatography, increased levels of neutral amino acids (e.g., glutamine, valine, phenylalanine, leucine, asparagine, citrulline, isoleucine, threonine, alanine, serine, histidine, tyrosine, tryptophan) and indican are found in the urine.
- Increased urinary Indican can be tested by Obermayer test.
- High-protein diet
- Physical and chemical protection from sunlight
- Patients also should avoid other aggravating factors, such as photosensitizing drugs, as much as possible.
- In patients with niacin deficiency and symptomatic disease, daily supplementation with nicotinic acid or nicotinamide
- Neurologic and psychiatric treatment is needed in patients with severe central nervous system involvement.