<prompt> All are true regarding subacute combined immunodeficiency except:Due to deficiency of adenosine deaminaseToxicity of leucocytes due to accumulation of cAMPBoth cellular and humoral immunity affectedBone marrow transplantation is the treatment  <response>: Ans: B Toxicity of leucocytes due to accumulation of cAMP Ref: Net sons Textbook of Pediatries. 19th Edition, Page:Explanation:Marked accumulations of adenosine, 22 - deoxyadenosine, and 22 -O-methyladenosine lead directly or indirectly to T-cell apoptosis, which causes the immunodeficiency Ref: Net sonSevere Combined Immunodeficiency SODBoth cellular and humoral immunity affectedMC type is X-linked SCID X-SCD due to mutation in Common Cytokine Receptor g Chain gCSecond most common form of SCID is absence of the enzyme adenosine deaminase ADA 15 patientsAll patients with SCID have very small thymuses 1 gThymus fail to descend from the neck, contain no thymocytes, and lack corticomedullary distinction or Hassall corpuscles.The thymic epithelium appears histologically normal.Both the follicular and paraeortical areas of the spleen are depleted of lymphocytes.Lymph nodes, tonsils, adenoids, and Peyer patches are absent or extremely underdevelopedClinical ManifestationsAffected infants present within the 1st few months of life with- Recurrent or persistent diarrhea- Pneumonia- Otitis media- Sepsis- Cutaneous infections- Growth failurePersistent infections with opportunistic organisms including lead to deathCandida albicansPneumocystis jiroveciParainfluenza 3 virusAdenovirusRespiratory syncytial virusRotavirus vaccine virusCytomegalovirus CM VEpstein- Barr virus EB V Varicella-zoster virusMeasles virusMMR-V vaccine virusBacillus Calmette-Guerin BCGAffected infants also lack the ability to reject foreign tissue and are therefore at risk for severe or fatal graft versus host disease GVHD from T lymphocytes in nonirradiated blood products or in allogeneic stem cell transplants or less severe GVHD from maternal immunocompetent T cells that crossed the placenta while the infant was in utero.These infants also have an absence of lymphocyte proliferative responses to mitogens, antigens, and allogeneic cells in vitro.Patients with adenosine deaminase ADA deficiency have the lowest absolute lymphocyte counts, usually 500mm3.Serum immunoglobulin concentrations are low or absentNo antibodies are formed after immunizations.T cells are extremely low or absentTreatmentSCID is a true pediatric emergency.Unless immunologic reconstitution is achieved through stem cell transplantation, death usually occurs during the 1 st yr of life and almost invariably before 2 yr of age. 