The use of alanine, free carnitine and IGFBP-1 as potential biomarkers for glycogen storage disease type I

ABSTRACT

Background: Glycogen Storage Disease Ia (GSDIa) and Ib (GSDIb) are inborn errors of carbohydrate metabolism due to a deficiency of glucose-6-phosphatase (G6Pase) or glucose-6-phosphate translocase (G6PT), respectively. Consuming prescribed amounts of uncooked cornstarch (UCCS) to prevent hypoglycemia is the standard of care for GSDIa and GSDIb. Patients followed in our GSD Program are admitted to the hospital annually for evaluation of their metabolic control by measuring glucose and lactate levels and revising treatment regimens accordingly. Lack of bed space due to the COVID-19 pandemic has created a need for alternate markers of metabolic control as lactate measurements are unreliable in the outpatient setting. This research aims to identify alternative biomarkers to show degree of metabolic control in individuals with GSDI. Method(s) A retrospective chart review was conducted on 45 adults and children with GSDI using data from January 1, 2014 toMay 6, 2021. Plasma alanine and free carnitine levels were compared with laboratory reference ranges. Results from the three tests were not available on every subject. Plasma alanine was evaluated on 24 subjects (16-GSDIa, 8-GSDIb) and free carnitine was evaluated on 25 subjects (17-GSDIa, 8-GSDIb). Result(s) Alanine levels in subjects with GSDIa ranged from 378 to 786 umol/L, while alanine levels in subjects with GSDIb ranged from 254 to 506 umol/L (reference range = 103-528 umol/L). Free carnitine levels ranged from26 to 72 umol/L in subjects with GSDIa and from 44 to 90 umol/L in subjects with GSDIb (reference range = 19-55 umol/L). Conclusion(s) Our analysis showed that plasma alanine and free carnitine have potential to be used as biomarkers of metabolic control. For plasma alanine, there seemed to be differences between subjects with GSDIa and GSDIb, as the majority of subjects with GSDIa had elevations in plasma alanine, while subjects with GSDIb did not. Elevated plasma alanine levels indicate lactic acidosis. For GSDIb, we hypothesize that there may be some type of G6Pase enzyme activity that occurs outside of the endoplasmic reticulum. When looking at both groups, free carnitine levels were mostly elevated. This indicates that there could be inhibition of fatty acid oxidation.Copyright © 2022 Elsevier Inc. All rights reserved.