Metabolism USMLE Step 1 Practice Question

A 28-year-old female with a history of progressive hepatosplenomegaly and epistaxis was admitted to the hospital with severe pain in her right thigh of 3 days' duration. A similar episode occurred 5 months earlier. There is no family history of these symptoms, and her 2 siblings are unaffected. A CT scan reveals flaring of the right distal femur. Results of a neurologic examination are normal. A bone marrow biopsy demonstrates the cells characteristic of her disease (shown below - macrophages with crinkled paper appearance). What is the material accumulating abnormally in these cells?