Hydroxykynureninuria, also known as xanthurenic aciduria, is related to vertebral, cardiac, renal, and limb defects syndrome 2 and pellagra. An important gene associated with Hydroxykynureninuria is KYNU (Kynureninase), and among its related pathways/superpathways are Regulation of expression of SLITs and ROBOs and superpathway of tryptophan utilization. Affiliated tissues include skin and kidney, and related phenotypes are encephalopathy and abnormal circulating tryptophan concentration