Adenosine deaminase deficiency D81.3

"Severe combined immunodeficiency, T cell-negative (T-), B cell-negative (B-), natural killer cell-negative (NK-)" is due to an autosomal recessive inherited ADA deficiency. This enzyme defect causes a variable phenotypic spectrum (SCID), with the most severe form of SCID occurring in infancy (early onset) and usually leading to early death. Later manifestations have a milder course.

Finally, "partial" ADA deficiency occurs in a subset of immunocompetent individuals who have reduced enzyme activity in erythrocytes but retain substantial enzyme activity of 5% to 80% of normal in leukocytes and other nucleated cells (summary by Arredondo-Vega et al., 1994).

3 clinical forms are distinguished:

• Early onset - classic ADA deficiency (80% of cases): predominant manifestation in the first 3 months of life.ADA activity < 0.01%, clinically associated with skeletal malformations, renal and neurological disorders, hearing loss.
• Delayed onset (15% of cases): manifestation in 1.-2,LJ; ADA activity 1-2%.
• Late onset (5% of cases): manifestation in the 3rd-15th year of life. ADA activity in 3-5%; recurrent or persistent HSV infections, sinubronchial bacterial infections, autoimmune diseases.

ADA deficiency accounts for approximately 15% of all SCID cases and one-third of autosomal recessive SCID cases (Hershfield, 2003).

Evidence of ADA deficiency, T cells and B cells reduced, an indication may be given by unexplained deaths in the first year of life in the family.

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