SCID
See BMT

Problem: profoundly defective or absent T-cell and B-cell function; small thymus, lymphocyte-depleted spleen

Epidemiology: 1/50,000-100,000

Presentation:

• Most severe of all the recognized immuno deficiencies
• Usually presents within first 6 months of life
  • Baby is protected by passive immunity from mother for about 3 mos, when maternal IgG finally wears out (T1/2 of IgG is 28 days, effect lasts about 3 half-lives). At this time, normally, serum IgG starts to become derived from baby. IgM and IgA are also baby-derived.
  • 1^st infection presents at 3 mos, with otitis, strep pneumonia, viral or other.
  • Upon antibiotic treatment, the normal gut flora is wiped out, and candida proliferates. Candidal enteritis ensues, and diarrhea and FTT are common presenting symptoms.
  • eczema and seborrhea
• May develop severe bacterial-GN sepsis, fungal-candidal, aspergillus, P. jiroveci,or viral infections-CMV, disseminated varicella

Two Major Types

• X-linked recessive(XLR): 50% of all SCID

  • IL-2, 4, 7, 9, 15 receptors defective
  • Defective proliferation and maturation of lymphocytes
  • Early arrest of T-cells and NK cells
  • Immature B cells with defective isotypeswitching

• Autosomal Recessive: 50% of SCID

  • Adenosine DeaminaseDeficiency(15%): ADA deficiency results in metabolic poisoning of all cells, with most harmful effects on lymphocytes and lymphoid progenitors
  • Leads to T-cell apoptosis
  • Associated with chondro-osseous dysplasia(rib cage abnormalities and skeletal dysplasia)

Treatment:

• PPX: Bactrim
• BMT
• ADA replacement (PEG-ADA)
• IVIG
• Il-2 replacement
• No live virus vaccines
• Prognosis: death in the 1st year of life, unless BMT

Interesting Note: In normal fetuses, after the 13^th week of gestation the immune system works well enough to reject foreign cells (including maternal). In SCID babies who are not immunocompetent, the fetus cannot reject maternal blood, and will have maternal cells in their body at birth. In boys, some cells may be XX (maternally derived), in girls, looking at DNA fingerprinting (short tandem repeats), some of mom’s cells may be present.

See BMT