GM1 Gangliosidosis Type II: Results of a 10-Year Prospective Study

Purpose GM1 gangliosidosis (GM1) a lysosomal disorder caused by pathogenic variants in GLB1, is characterized by relentless neurodegeneration. There are no approved treatments. Methods Forty-one individuals with type II (late-infantile and juvenile) GM1 participated in a single-site prospective observational study. Results Classification of 37 distinct variants using ACMG criteria resulted in the upgrade of six and the submission of four new variants. In contrast to type I infantile disease, children with type II had normal or near normal hearing and did not have cherry red maculae or hepatosplenomegaly. Some older children with juvenile onset disease developed thickened aortic and/or mitral valves. Serial MRIs demonstrated progressive brain atrophy, more pronounced in late infantile patients. MR spectroscopy showed worsening elevation of myo-inositol and deficit of N-acetyl aspartate that were strongly correlated with scores on the Vineland Adaptive Behavior Scale, progressing more rapidly in late infantile than juvenile onset disease. Conclusion Serial phenotyping of type II GM1 patients expands the understanding of disease progression and clarifies common misconceptions about type II patients; these are pivotal steps toward more timely diagnosis and better supportive care. The data amassed through this 10-year effort will serve as a robust comparator for ongoing and future therapeutic trials.