This directed case study connects the physiological symptoms and genetic mutations associated with mucolipidosis II, a lysosomal storage disorder (LSD), to the mislocalization of certain lysosomal hydrolases caused by the lack of an important post-translational modification on these enzymes. Students follow the story of “Ana Sophia” through the perspective of Ana’s pediatrician. At Ana’s six-month well visit, Ana presents with symptoms consistent with an LSD including reduced mobility. Students follow the pediatrician’s process of confirming that a lysosomal storage disorder is the cause of Ana’s symptoms and identify her specific disorder. The case is designed for undergraduate students who have completed introductory biology courses and have foundational knowledge of protein structure, enzyme function, post-translational modifications, the endomembrane system, and the structure and function of the lysosome. Students review important concepts in cellular biology and then apply those concepts using critical and divergent thinking to explain disease symptomatology, generate hypotheses, interpret test results, conduct thought experiments, and synthesize newly acquired knowledge with additional research in a final written homework assignment.