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Updated: Mar 31 2019

Severe Combined Immunodeficiency Disorder (SCID)

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  • Snapshot
    • A 2-month-old baby boy is brought in for an urgent visit to the pediatrician. He has had several ear infections in his short lifetime and now seems to be struggling with a cold. On physical exam, his tongue is noted to be coated with white film. His scalp and face are covered with a flaky dandruff-like substance. Immediately concerned, his pediatrician orders a chest radiograph, which shows absence of thymic shadow. Flow cytometry is ordered.
  • Introduction
    • Combined B- and T-cell disorder causing immunodeficiency
    • Life-threatening disease of recurrent infections
    • Pathogenesis
      • multiple variants found
      • most common is X-linked defective common gamma chain
        • found in IL-2R, IL-4R, and IL-7R
        • defective T-cell activation
      • autosomal recessive adenosine deaminase deficiency
        • 2nd most common
        • ↑ deoxyadenosine, which is toxic to lymphocytes
        • ↓ DNA synthesis
      • autosomal recessive JAK3 deficiency
      • B-cells
        • decreased immunoglobulin production
      • T-cells
        • markedly decreased T-cells
  • Presentation
    • Symptoms
      • symptoms present < 3 months of age
      • failure to thrive
      • recurrent bacterial, viral, fungal, and protozoal infections
      • chronic diarrhea
    • Physical exam
      • may see thrush in mouth and diaper area
      • eczematous dermatitis
        • erythroderma (> 90% body surface area involvement)
      • severe seborrheic dermatitis
      • diffuse alopecia
      • absent lymphatic tissue, including tonsils and thymus
  • Evaluation
    • Diagnosis often delayed due to maternal IgG protecting baby in first few months of life
    • ↓ Lymphocyte count (< 3000/μL)
    • Chest radiography with no thymic shadow
    • Flow cytometry
      • absent T-cells
      • abnormal function of B-cells
  • Differential Diagnosis
    • Hypogammaglobulinemia
    • DiGeorge syndrome
    • Hyper-IgM syndrome
    • Ataxia-telangiectasia
  • Treatment
    • Bone marrow transplant
      • life-saving treatment
      • no concerns for allograft rejection
    • Gene therapy
  • Prognosis, Prevention, and Complications
    • Prognosis
      • without intervention, death by 2 years
      • patients < 6 months of age who receive transplant have the best outcomes
    • Complications
      • severe infection
      • death
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