Biochemical characterization of aspartylglucosaminidase missense variants of unclear significance reveals different degrees of functional impairment.

Prediction of the molecular consequences of missense variants in genetic diseases places a challenge, often resulting in ambiguous classifications by different algorithms. Thus, such variants of unclear significance (VUS) require a thorough molecular characterization to judge if they are pathogenic or not. Pathogenic variants in the AGA gene encoding for aspartylglucosaminidase (AGA) result in aspartylglucosaminuria (AGU), a lysosomal storage disorder. For a correct diagnosis, it is important to understand the effect of VUS found in AGU patients on the structure and function of the AGA enzyme. In this study, several AGA missense variants found in AGU patients were characterized by biochemical and bioinformatics methods. The pathogenicity of most of these variants was verified, but some of them exhibited only a minor pathogenic effect on AGA function. Especially the Leu126Val variant showed a high residual AGA activity, and a homozygous patient with this variant has a mild AGU phenotype with atypical symptoms. In the era of personalized medicine, our data stress the importance of molecular characterization of unclear genetic variants for the choice of best treatment options.