Hartnup Disease Workup

Updated: Nov 12, 2021
  • Author: Lidija Kandolf Sekulovic, MD, PhD; Chief Editor: William D James, MD  more...
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Laboratory Studies

With urine chromatography, [3, 22, 23, 26, 29] increased levels of neutral amino acids (eg, glutamine, valine, phenylalanine, leucine, asparagine, citrulline, isoleucine, threonine, alanine, serine, histidine, tyrosine, tryptophan) and indican are found in the urine. Urinary indoxyl derivatives (ie, 5-hydroxyindoleacetic acid) may be demonstrated following an oral tryptophan load. Urine excretion of proline, hydroxyproline, and arginine remains normal, which differentiates Hartnup disease from other causes of gross aminoaciduria. Perform urine chromatography to exclude nutritional pellagra.

Plasma concentrations of amino acids are usually normal. [3, 22, 23, 26, 29]



Jejunal biopsy may be required in selected patients (transport defect may be identified in vitro). Skin biopsy may be required in selected patients. [23, 25, 26, 27]


Histologic Findings

Changes in the skin are similar to those seen in pellagra. Findings are not diagnostic and include hyperkeratosis, parakeratosis, epidermal atrophy, hyperpigmentation of the basal layer, and a mild superficial dermal lymphocytic infiltrate. Bullae may be either intraepidermal or subepidermal. Hyperplasia of the sebaceous glands with follicular dilatation and plugging may occur. [25, 26, 27]