Hartnup disease is characterized by inability of body to absorb certain amino acids. The lack of these amino acids leads to decrease in the production of vitamins and proteins. Individuals with Hartnup disease have aminoaciduria. Other signs and symptoms include skin rashes, ataxia, psychosis, and depression. Reference: https://medlineplus.gov/genetics/condition/hartnup-disease/#synonyms Image via: https://healthjade.net/hartnup-disease/