NIH

Zebra of the Week: Tryptophan malabsorption syndrome

March 16, 2026

Tryptophan malabsorption syndrome (blue diaper syndrome) is a rare inherited metabolic disorder marked by defective intestinal absorption of tryptophan, leading to indicanuria and characteristic blue‑stained diapers. Affected infants, typically presenting in the newborn- or early-infant period, may develop gastrointestinal symptoms, fever, irritability, failure to thrive, visual abnormalities, and hypercalcemia, which can progress to nephrocalcinosis and potential renal impairment. The biochemical defect remains incompletely defined, but current evidence points to impaired tryptophan absorption and transport, with possible involvement of LAT2 and TAT1 variants.

The condition is classified as an inherited metabolic and genetic disease, and reported inheritance patterns include autosomal recessive and X‑linked recessive.

Source:

(Accessed 2026, March 13). NIH Genetic and Rare Diseases Information Center (GARD).. Tryptophan malabsorption syndrome. https://rarediseases.info.nih.gov/diseases/5939/tryptophan-malabsorption-syndrome