Specific Antibody Deficiency (SAD)/Specific Polysaccharide Antibody Deficiency (SPAD)

Physiology

  • Poor serological response to polysaccharide antigens (with normal levels of immunoglobulins and IgG subclasses) and normal responses to protein antigens
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Clinical

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  • Specific antibody deficiency (SAD) is an immune deficiency which has been reported in adults and children with recurrent respiratory tract infections; however, the clinical features of SAD are not well described. This study evaluated formally the clinical syndrome of SAD, by comparing the clinical features of children with SAD and those of children with recurrent infection but normal immune function tests. SAD was defined as an adequate IgG antibody response to less than 50% of 12 pneumococcal serotypes tested following 23-valent unconjugated pneumococcal immunization. An adequate IgG antibody response was defined as a post-immunization titre of ≥ 1·3 µg/ml or ≥ four times the preimmunization value. Seventy-four children with recurrent infection were evaluated where immune deficiencies other than SAD had been excluded. Eleven (14·9%) of these children had SAD. Clinical features differed between the group with SAD and the group with normal antibody responses. A history of otitis media, particularly in association with chronic otorrhoea was associated with SAD [relative risk (RR) of SAD in those with chronic otorrhoea 4·64 (P = 0·02)]. SAD was associated with allergic disease, particularly allergic rhinitis [RR of SAD in those with allergic rhinitis 3·77 (P = 0·04)]. These two clinical associations of SAD were independent in this study [RR of chronic otorrhoea in those with allergic rhinitis 0·85 (P = 0·28)]. SAD was not an age-related phenomenon in this population. SAD has a distinct clinical phenotype, presenting as recurrent infection associated with chronic otorrhoea and/or allergic disease, and the condition should be sought in children with these features.


References

  • The clinical syndrome of specific antibody deficiency in children. Clin Exp Immunol. 2006 December; 146(3): 486–492 [MEDLINE]