Severe combined immunodeficiency

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Summary of Severe combined immunodeficiency

Severe combined immunodeficiency is the most severe form of primary immunodeficiencies, and may results from an X-linked recessive defect in IL-2R gamma chain or an autosomal recessive defect in adenosine deaminase deficiency. This disorder results in B-cell and T-cell disorders, resulting in the failure to thrive, chronic diarrhea, thrush, and recurrent infections.

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Severe combined immunodeficiency

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DIAGNOSIS TREATMENT OTHER INTERVENTIONS LAB RESULTS ▪ Measures to prevent infections, HSCT ▪ Gene therapy, enzyme replacement therapy (less effective) ▪ SCID ▫ Decreased ADA blood levels OTHER DIAGNOSTICS ▪ Genetic testing SEVERE COMBINED IMMUNODEFICIENCY (SCID) osms.it/SCID PATHOLOGY & CAUSES ▪ Rare genetic syndrome; disturbance in cellmediated, humoral immunity ▪ Combined defects in T, B lymphocyte development, function → severe immunodeﬁciency CAUSES ▪ Underlying causes vary in different forms of SCID ▪ Cytokine receptor defects, adenosine deaminase (ADA) deﬁciency (most common) ▪ Cytokine receptor defects (50–60% of cases) ▫ Mutation in gene encoding common γ-chain subunit of interleukin (IL) receptors (IL-2 receptor gamma/IL-2Rγ) ▪ Impaired interleukin signaling required for survival, development, proliferation of lymphocytes (esp. T lymphocytes) ▪ Profound decrease in lymphocyte count (esp. T, NK-cells) ▪ B lymphocyte count can be normal, immunoglobulin synthesis defective due to lack of T helper cells 188 OSMOSIS.ORG RISK FACTORS ▪ X-linked recessive pattern of inheritance, more common in individuals who are biologically male COMPLICATIONS ▪ Susceptibility to recurrent, severe infections by wide range of microorganisms ▫ Candida albicans, Pneumocystis jiroveci, Pseudomonas, cytomegalovirus, varicella ▪ Without HSCT, death may occur within ﬁrst year due to fatal infections SIGNS & SYMPTOMS ▪ Recurrent infections ▪ Oral candidiasis presenting with prominent thrush ▪ Chronic diarrhea → malabsorption, failure to thrive ▪ Extensive rash ▪ Morbilliform rash due to reaction of maternal T cells against fetus → graft versus host disease (GVHD)

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Severe combined immunodeficiency

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USMLE® Step 1 style questions USMLE

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A 12-month-old boy is brought to the emergency room by his mother because of recurrent episodes of fever, chills, diarrhea, and failure to grow. He was born term and appeared normal at infancy; however, the mother explains she had not received prenatal care and had delivered her child at home. His temperature is 39.4°C (104.0°F), pulse is 140/min, respirations are 31/min, and blood pressure is 120/80 mm Hg. Chest X-ray shows an absent thymic shadow. The absolute lymphocyte count is well below the lower limit of normal. Medical records indicate he was diagnosed with severe combined immunodeficiency (SCID) when he was 5-months-old, but the patient was lost to follow-up. Hematopoietic cell transplantation is considered as the next step in management. Which of the following choices is true regarding bone marrow transplant in this patient?

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