Immunoglobulin (Ig) A deficiency has long been recognized in patients with chromosome 18 abnormalities. We present the case of a young girl in whom a chromosome 18p deletion syndrome (46,XX,del[18][p11.1]) was associated not only with IgA deficiency, but also with an inability to make antibody to the unconjugated pneumococcal polysaccharide vaccine, Pneumovax II, indicating a concomitant specific polysaccharide antibody deficiency. The patient suffered from recurrent upper respiratory tract and genitourinary infections, which were controlled by the use of prophylactic antibiotics. The association of specific polysaccharide antibody deficiency, IgA deficiency, and
chromosome 18p deletion syndrome has not been described previously, and extends the immunological phenotype of antibody deficiencies associated with defects of chromosome 18. The presence of specific polysaccharide antibody deficiency should be investigated in patients with chromosome 18 abnormalities, as these patients may have a more severe spectrum of infections than patients with chromosome 18 abnormalities and selective IgA deficiency alone.

Key words: Chromosome 18. 18p deletion syndrome. IgA defi ciency. Specifi c polysaccharide antibody defi ciency. Antibody defi ciency.