Arginine does not rescue p.Q188R mutation deleterious effect in classic galactosemia

Abstract

BackgroundClassic galactosemia is a rare genetic metabolic disease with an unmet treatment need. Current standard of care fails to prevent chronically-debilitating brain and gonadal complications.Many mutations in the GALT gene responsible for classic galactosemia have been described to give rise to variants with conformational abnormalities. This pathogenic mechanism is highly amenable to a therapeutic strategy based on chemical/pharmacological chaperones. Arginine, a chemical chaperone, has shown beneficial effect in other inherited metabolic disorders, as well as in a prokaryotic model of classic galactosemia.The p.Q188R mutation presents a high prevalence in the Caucasian population, making it a very clinically relevant mutation. This mutation gives rise to a protein with lower conformational stability and lower catalytic activity. The aim of this study is to assess the potential therapeutic role of arginine for this mutation.MethodsArginine aspartate administration to four patients with the p.Q188R/p.Q188R mutation, in vitro studies with three fibroblast cell lines derived from classic galactosemia patients as well as recombinant protein experiments were used to evaluate the effect of arginine in galactose metabolism. This study has been registered at https://clinicaltrials.gov (NCT03580122) on 09 July 2018. Retrospectively registered.ResultsFollowing a month of arginine administration, patients did not show a significant improvement of whole-body galactose oxidative capacity (p = 0.22), erythrocyte GALT activity (p = 0.87), urinary galactose (p = 0.52) and urinary galactitol levels (p = 0.41). Patients’ fibroblasts exposed to arginine did not show changes in GALT activity. Thermal shift analysis of recombinant p.Q188R GALT protein in the presence of arginine did not exhibit a positive effect.ConclusionsThis short pilot study in four patients homozygous for the p.Q188R/p.Q188R mutation reveals that arginine has no potential therapeutic role for galactosemia patients homozygous for the p.Q188R mutation.Electronic supplementary materialThe online version of this article (10.1186/s13023-018-0954-8) contains supplementary material, which is available to authorized users.

PI3K inhibitors: review and new strategies

“…As such they have been dubbed “natural gene therapy” and “nature's proof of principle that you can fix those mutations” in the case of Wiskott–Aldrich syndrome (WAS). 97 Additional examples include the p.Q188R mutation in classic galactosemia 98 that gives rise to a protein with lower conformational stability and lower catalytic activity 99 and p53. 100 Drugs mimicking the allosteric effects of these mutants may rescue function.…”

Current and Future Treatments for Classic Galactosemia

“…Arginine supplementation, known for its effect as an aggregation inhibitor [ 82 ] has been studied as a potential therapeutic approach for classic galactosemia. Despite promising results of this chemical chaperone in a bacterial model [ 83 ], in a pilot study with 4 patients carrying the NM_000155.4: c.563A>G (p.Gln188Arg) mutation, arginine did not lead to improved GALT stability nor GALT activity levels as there was no improvement in galactose oxidation capacity [ 4 , 84 ].…”

Galactosemia: Towards Pharmacological Chaperones

“…Initial studies suggested that non-specific binding of the amino acid arginine stabilises GALT [ 100 ]. Unfortunately, further work demonstrated that this is not the case [ 101 ]. In contrast, PCs bind to specific sites.…”