Primary Amyloidosis: This condition is characterized by the deposition of amyloid proteins in various tissues, leading to organ dysfunction. The combination of osteopenia (due to amyloid deposition in bone), splenomegaly (enlarged spleen), and hypoglobulinemia (low levels of globulins, which are a type of protein) can be seen in primary amyloidosis, particularly the AL type, which affects multiple systems and can lead to these manifestations.

Chronic Lymphocytic Leukemia (CLL): CLL can cause hypoglobulinemia due to the suppression of normal antibody production by the malignant lymphocytes. Splenomegaly is common in CLL due to the accumulation of these cells. Osteopenia might be less directly related but can occur due to the chronic nature of the disease or associated treatments.
Multiple Myeloma: Although more commonly associated with hyperglobulinemia (high levels of globulins), some forms of myeloma can present with hypoglobulinemia. Osteopenia or osteolytic lesions are characteristic due to the proliferation of malignant plasma cells in the bone marrow. Splenomegaly can occur but is less common.
Autoimmune Lymphoproliferative Syndrome (ALPS): This rare condition is characterized by an accumulation of lymphocytes, leading to lymphadenopathy and splenomegaly. Hypoglobulinemia can occur, and while osteopenia is not a primary feature, it might be seen in the context of chronic disease or associated autoimmune phenomena.

HIV Infection: HIV can cause a range of immune dysfunctions, including hypoglobulinemia, and is associated with various opportunistic infections and conditions that might lead to splenomegaly. Osteopenia can occur due to the chronic infection, antiretroviral therapy, or associated conditions like osteonecrosis.
Sickle Cell Disease: While primarily known for causing anemia and painful crises, sickle cell disease can lead to splenomegaly early in life due to the sequestration of red blood cells. Over time, autosplenectomy (functional asplenia) might occur, but before this, there can be a phase of splenomegaly. Osteopenia can result from chronic hemolysis and hypogonadism, and hypoglobulinemia might be seen due to splenic dysfunction.

Gaucher's Disease: A genetic disorder leading to the accumulation of glucocerebroside in cells, causing splenomegaly, bone marrow infiltration (which can lead to osteopenia), and occasionally hypoglobulinemia due to immune dysfunction.
Niemann-Pick Disease: Another genetic disorder that affects lipid metabolism, leading to the accumulation of sphingomyelin in cells. It can cause splenomegaly, and in some types, there might be associated osteopenia and immune system dysfunction leading to hypoglobulinemia.
Lysosomal Storage Diseases: A group of disorders that can lead to the accumulation of toxic substances within cells, affecting multiple organ systems, including the spleen and bone, potentially causing the triad of osteopenia, splenomegaly, and hypoglobulinemia.