Lysosomal exoglycosidases are responsible for processing endocytosed glycans from the non-reducing end to produce the corresponding monosaccharides. Genetic mutations in a particular lysosomal glycosidase may result in accumulation of its particular substrate, which may cause diverse lysosomal storage disorders. The identification of effective therapeutic modalities to treat these diseases is a major yet poorly realised objective in biomedicine. One common strategy comprises the identification of effective and selective competitive inhibitors that may serve to stabilize the proper folding of the mutated enzyme, either during maturation and trafficking to, or residence in, endo-lysosomal compartments. The discovery of such inhibitors is greatly aided by effective screening assays, the development of which is the focus of the here-presented work. We developed and applied fluorescent activity-based probes reporting on either human GH30 lysosomal glucosylceramidase (GBA1, a retaining β-glucosidase) or GH31 lysosomal retaining α-glucosidase (GAA). FluoPol-ABPP screening of our in-house 358-member iminosugar library yielded compound classes selective for either of these enzymes. In particular, we identified a class of N-alkyldeoxynojirimycins that inhibit GAA, but not GBA1, and that may form the starting point for the development of pharmacological chaperone therapeutics for the lysosomal glycogen storage disease that results from genetic deficiency in GAA: Pompe disease.

Danon disease (DD) is a rare X-chromosome-linked dominant lysosomal glycogen storage disease. Its features have seldom been reported by using cardiac MRI. This case series aimed to evaluate cardiac features of DD on the basis of MRI observations from five centers in China. From January 2010 to May 2019, 16 patients with DD (13 male patients [81%]; median age, 19 years; age range, 14-44 years) underwent MRI. The most frequent DD cardiomyopathy manifestation was symmetric hypertrophy cardiomyopathy (HCM) phenotype (nine of 16; 56%), followed by asymmetric HCM phenotype (six of 16; 38%) and dilated cardiomyopathy phenotype (one of 16; 6%). The characteristic late gadolinium enhancement features included midbasal septum sparing (14 of 16; 88%) and apex involvement (16 of 16; 100%) with a base-to-apex increasing tendency, free wall involvement (15 of 16; 94%), and extensive subendocardium involvement (14 of 16; 88%). Abnormal T2 signal (seven of 16; 44%) and resting perfusion defect (14 of 16; 88%) were not uncommon in patients with DD. Furthermore, the cardiac MRI features of DD cohort in this study were compared with those of DD in previous literature and with genetically confirmed sarcomeric HCM.

Pompe disease is an autosomal recessive, lysosomal glycogen storage disease caused by acid α-glucosidase deficiency. Infantile-onset Pompe disease (IOPD) is the most severe form and is characterized by cardiomyopathy, respiratory distress, hepatomegaly, and skeletal muscle weakness. Untreated, IOPD generally results in death within the first year of life. Enzyme replacement therapy (ERT) with recombinant human acid alpha glucosidase (rhGAA) has been shown to markedly improve the life expectancy of patients with IOPD. However, the efficacy of ERT in patients with IOPD is affected by the presence of symptoms and cross-reactive immunologic material (CRIM) status. We have treated two siblings with IOPD with ERT at different ages: the first was symptomatic and the second was asymptomatic. The female proband (Patient 1) was diagnosed with IOPD and initiated ERT at 4 months of age. Her younger sister (Patient 2) was diagnosed with IOPD at 10 days of age and initiated ERT at Day 12. Patient 1, now 6 years old, is alive but bedridden, and requires 24-hour invasive ventilation due to gradually progressive muscle weakness. In Patient 2, typical symptoms of IOPD, including cardiac failure, respiratory distress, progressive muscle weakness, hepatomegaly and myopathic facial features were largely absent during the first 12 months of ERT. Her cardiac function and mobility were well-maintained for the first 3 years, and she had normal motor development. However, she developed progressive hearing impairment and muscle weakness after 3 years of ERT. Both siblings have had low anti-rhGAA immunoglobulin G (IgG) antibody titers during ERT and have tolerated the treatment well. These results suggest that initiation of ERT during the pre-symptomatic period can prevent and/or attenuate the progression of IOPD, including cardiomyopathy, respiratory distress, and muscle weakness for first several years of ERT. However, to improve the long-term efficacy of ERT for IOPD, new strategies for ERT for IOPD, e.g. modifying the enzyme to enhance uptake into skeletal muscle and/or to cross the blood brain barrier (BBB), will be required.