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Abstract With the expansion of newborn screening efforts for MPS disorders, the number of identified variants of uncertain significance in IDUA continues to increase. To better define functional consequences of identified IDUA variants, we developed a HEK293-based expression platform that can be used to determine the relative specific activity of variant α-iduronidases by combining a fluorescence-based activity assay and semi-quantitative western blotting. We employed the current platform to characterize over thirty different IDUA variants, including known benign and pathogenic variants, as well as multiple variants of uncertain significance identified through newborn screening. This analysis allowed the stratification of variant enzymes based on their relative specific activity, and uncovered distinct effects of the different variants on enzyme folding, processing, and stability. While relative specific activity serves as a useful first-level test for enzyme function, our observations reinforce the need for secondary analyses of enzyme function to fully assess variant pathogenicity.

Summary: The classic view of the lysosome as a static recycling center has been replaced with one of a dynamic and mobile hub of metabolic regulation. This revised view raises new questions about how dysfunction of this organelle causes pathology in inherited lysosomal disorders. Here we provide evidence for increased lysosomal exocytosis in the developing cartilage of three lysosomal disease zebrafish models with distinct etiologies. Dysregulated exocytosis was linked to altered cartilage development, increased activity of multiple cathepsin proteases, and cathepsin- and TGFβ-mediated pathogenesis in these models. Moreover, inhibition of cathepsin activity or direct blockade of exocytosis with small molecule modulators improved the cartilage phenotypes, reinforcing a connection between excessive extracellular protease activity and cartilage pathogenesis. This study highlights the pathogenic consequences in early cartilage development arising from uncontrolled release of lysosomal enzymes via exocytosis, and suggests that pharmacological enhancement of this process could be detrimental during tissue development.

Purpose: The specialty of Laboratory Genetics and Genomics (LGG) was created in 2017 in an effort to reflect the increasing convergence in technologies and approaches between clinical molecular genetics and clinical cytogenetics. However, there has not yet been any formal evaluation of the merging of these disciplines and the challenges faced by Program Directors (PDs) tasked with ensuring the successful training of laboratory geneticists under the new model. Methods: An electronic multi-question Qualtrics survey was created and was sent to the PD for each of the Accreditation Council for Graduate Medical Education–accredited LGG fellowship programs at the time. The data were collected, and the responses were aggregated for each question. Results: All of the responding PDs had started training at least 1 LGG fellow. PDs noted challenges with funding, staff shortages, molecular/cytogenetics content integration, limited total training time, increased remote work, increased sendout testing, and a lack of prior cytogenetics knowledge among incoming fellows. Conclusion: This survey attempted to assess the challenges that LGG PDs have been facing in offering and integrating clinical molecular genetics and clinical cytogenetics fellowship training. Common challenges between programs were noted, and a set of 6 concluding comments are provided to facilitate future discussion.