<unk>  are a set of<unk>  characterized by the abnormal proliferation of lymphocytes into a monoclonal lymphocytosis. The two major types of lymphocytes are B cells and T cells, which are derived from pluripotent hematopoietic stem cells in the bone marrow. Individuals who have some sort of dysfunction with their immune system are susceptible to develop a<unk> because when any of the numerous control points of the immune system become dysfunctional, immunodeficiency or deregulation of lymphocytes is more likely to occur. There are several inherited gene mutations that have been identified to cause<unk> ; however, there are also acquired and iatrogenic causes. X-linked<unk> A mutation on the X chromosome is associated with a T cell and natural killer cell<unk>  Autoimmune<unk> Some children with autoimmune<unk>  are heterozygous for a mutation in the gene that codes for the Fas receptor, which is located on the long arm of chromosome 10 at position 24.1, denoted 10q24.1. This gene is member 6 of the TNF-receptor superfamily (TNFRSF6). The Fas receptor contains a death domain and has been shown to play a central role in the physiological regulation of programmed cell death. Normally, stimulation of recently activated T cells by antigen leads to coexpression of Fas and Fas receptor on the T cell surface. The engagement of Fas by Fas receptor results in apoptosis of the cell and is important for eliminating T cells that are repeatedly stimulated by antigens. As a result of the mutation in the Fas receptor gene, there is no recognition of Fas by Fas receptor, leading to a primitive population of T cells that proliferates in an uncontrolled manner. Other inherited causes Boys with X-linked immunodeficiency syndrome are at a higher risk of mortality associated with Epstein–Barr virus infections, and are predisposed to develop a<unk> or lymphoma. Children with common variable immunodeficiency (CVID) are also at a higher risk of developing a<unk>  Some<unk>  that predispose a person to<unk>  are severe combined immunodeficiency (SCID), Chédiak–Higashi syndrome, Wiskott–Aldrich syndrome (an X-linked recessive<unk> , and ataxia–telangiectasia. Even though ataxia telangiectasia is an autosomal recessive<unk>  people who are heterozygotes for this still have an increased risk of developing a<unk>  Acquired causes Viral infection is a very common cause of<unk> . In children, the most common is believed to be congenital HIV infection because it is highly associated with acquired immunodeficiency, which often leads to<unk> . Iatrogenic causes There are many<unk>  that are associated with organ transplantation and immunosuppressant therapies. In most reported cases, these cause B cell<unk> ; however, some T cell variations have been described. The T cell variations are usually caused by the prolonged use of T cell suppressant drugs, such as sirolimus, tacrolimus, or ciclosporin. The Epstein-Barr virus, which infects >90% of the world population, is also a common cause of these<unk> , being responsible for a wide range of non-malignant, pre-malignant, and malignant Epstein-Barr virus-associated<unk>  diseases.
Lymphoproliferative disorders
Myeloproliferative neoplasm
Tumors of the hematopoietic and lymphoid tissues
Childhood leukemia
B-cell leukemia
Autoimmune neutropenia
Immunoproliferative disorder
Non-Hodgkin lymphoma