We report a 5-year-old girl with
adenosine deaminase (
ADA) deficiency who was asymptomatic during the first years of life. At 3 years of age, she developed chronic and recurrent sinopulmonary
infections, and at 4 1/2 years of age she had one major
infection with Streptococcus pneumoniae (
bacteremia and
septic arthritis of the hip). Immunologic evaluation at 5 years of age revealed persistent
lymphopenia, decreased helper-suppressor T cell ratios, and low proliferative responses to
mitogens. The
IgG,
IgM, and
IgA levels were normal; the
IgG2 level was low normal or below normal. The patient had specific
antibodies against
toxoids and
viral antigens but failed to produce
antibodies against Haemophilus influenzae type b and pneumococcal
polysaccharides. Although no symptoms of
allergy were present, she had persistent
eosinophilia and elevated
IgE levels. The patient had 0.6% of normal ADA activity in erythrocytes and approximately 1% of normal ADA activity in peripheral blood mononuclear cells. Beginning at 6 years of age, she was treated with weekly
injections of
polyethylene glycol-modified bovine ADA. This treatment was well tolerated and effectively reversed the biochemical consequence of
ADA deficiency. Concomitantly, she improved clinically and her T lymphocyte numbers and blastogenic responses to
mitogens in vitro became normal. The late onset of clinical symptoms and relatively benign
clinical course in this patient emphasize the need to consider
ADA deficiency in a broad spectrum of immunodeficient children.