CASE 1: Ms. Amara Diallo, a 27-year-old woman, has sickle cell disease (HbSS). She takes hydroxyurea 1000 mg daily and folic acid, has had several painful crises, and was admitted to hospital last year with acute chest syndrome. Her hematologist has told her that her spleen 'no longer works'. Her oral mucosa is pale, her sclerae are slightly yellow, and she has generalized 4-5 mm pockets with bleeding. Her radiographs show enlarged marrow spaces between the premolar roots, crossed by thick horizontal trabeculae in a 'stepladder' pattern. The lamina dura is intact and she has no symptoms in the area. What is the MOST likely explanation?