Peptide tyrosine tyrosine levels are increased in patients with urea cycle disorders.

Nutritional management is essential for patients with inborn errors of metabolism, such as urea cycle disorders (UCDs). Lack of appetite is common in these patients and can lead to underconsumption of calories, catabolism, and subsequently loss of metabolic control. The etiology of anorexia in these patients is largely unexplored. The neuroendocrine hormone peptide tyrosine tyrosine (PYY), secreted postprandially from endocrine cells of the ileum and colon, induces feelings of satiety and decreases food intake. While plasma PYY levels have been characterized in a number of populations, they have not been examined in UCD patients. In a retrospective study, plasma PYY concentrations were measured in UCD (n=42) patients and controls (n=28) via an ELISA to determine if levels of this anorexigenic hormone are altered in this patient population. Median PYY levels were significantly higher in UCD patients compared to controls (p=3.5×10(-5)). Body mass index was significantly associated with increased PYY levels in controls (p=0.02), while UCD diagnosis subtype was associated with PYY levels (p=1×10(-3)) in cases. Median PYY levels were significantly lower in ornithine carbamoyltransferase deficient patients compared with all other UCD subtypes (p=9×10(-3)), but significantly higher compared to controls (p=1.6×10(-3)). Overall, this study demonstrates that UCD cases have increased PYY levels compared to controls, suggesting that regulation of PYY may be altered in these patients. These observations may lead to a better understanding of the development of anorexia in UCD patients.