GM1 gangliosidosis type II: Results of a 10-year prospective study.

Objective: 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 American College of Medical Genetics and Genomics criteria resulted in the upgrade of 6 and the submission of 4 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 magnetic resonance images demonstrated progressive brain atrophy, more pronounced in late infantile patients. Magnetic resonance 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 compared with juvenile onset disease.

Conclusions: 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.