Hartnup Disease

INTRODUCTION:
  • 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+.
ETIOLOGY:
  • 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: 
  1. Failure to thrive, 
  2. Photosensitivity, 
  3. Intermittent ataxia, 
  4. 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
RISK FACTORS:
  • Symptoms may be triggered by:
  1. Sunlight, 
  2. Fever, 
  3. Drugs, or 
  4. Emotional or physical stress. 
  5. Poor nutrition  
  6. Deficiency of niacinamide. 
 DIAGNOSIS:
  • 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.
TREATMENT:
  • 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.
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