Arginine to ornithine ratio as a diagnostic marker in patients with positive newborn screening for hyperargininemia

• Type of Material: Article
• Authors: Yue Huang, University of California Los Angeles; Rajesh Sharma, Quest Diagnostics Nichols Institute; Annette Feigenbaum, University of California San Diego; Chung Lee, Stanford University; Inderneel Sahai, University of Massachusetts; Rossana Sanchez Russo, Emory University; Juanita Neira, Emory University; Susan Sklower Brooks, Rutgers State University; Kelly E. Jackson, University of Louisville; Derek Wong, University of California Los Angeles; Stephen Cederbaum, University of California Los Angeles; Felicitas L. Lacbawan, Quest Diagnostics Nichols Institute; Charles M. Rowland, Quest Diagnostics Nichols Institute; Pranoot Tanpaiboon, Quest Diagnostics Nichols Institute; Denise Salazar, Quest Diagnostics Nichols Institute
• Language: English
• Date: 2021-03-04
• Publisher: Elsevier
• Publication Version: Final Published Version
• Copyright Statement: © 2021 Published by Elsevier Inc.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.ymgmr.2021.100735
• Title of Journal or Parent Work: Molecular Genetics and Metabolism Reports
• Volume: 27
• Grant/Funding Information: None.
• Keywords: Newborn screening; Arg/Orn ratio; Ornithine; NBS; Arginase deficiency; Arginine
• Research Categories: Health Sciences, Human Development; Biology, Genetics

Abstract

Arginase deficiency is a rare inborn error of metabolism that interrupts the final step of the urea cycle. Untreated individuals often present with episodic hyperammonemia, developmental delay, cognitive impairment, and spasticity in early childhood. The newborn screening (NBS) algorithms for arginase deficiency vary between individual states in the US but often include hyperargininemia and elevated arginine to ornithine (Arg/Orn) ratio. Here, we report 14 arginase deficiency cases, including two patients with positive NBS for hyperargininemia in whom the diagnosis of arginase deficiency was delayed owing to normal or near normal plasma arginine levels on follow-up testing. To improve the detection capability for arginase deficiency, we evaluated plasma Arg/Orn ratio as a secondary diagnostic marker in positive NBS cases for hyperargininemia. We found that plasma Arg/Orn ratio combined with plasma arginine was a better marker than plasma arginine alone to differentiate patients with arginase deficiency from unaffected newborns. In fact, elevated plasma arginine in combination with an Arg/Orn ratio of ≥1.4 identified all 14 arginase deficiency cases. In addition, we examined the impact of age on plasma arginine and ornithine levels. Plasma arginine increased 0.94 μmol/L/day while ornithine was essentially unchanged in the first 31 days of life, which resulted in a similar increasing trend for the Arg/Orn ratio (0.01/day). This study demonstrated that plasma Arg/Orn ratio as a secondary diagnostic marker improved the detection capability for arginase deficiency in newborns with hyperargininemia, which will allow timely detection of arginase deficiency and hence initiation of treatment before developing symptoms.