Elevated serum concentrations of β‐tryptase, but not α‐tryptase, in Sudden Infant Death Syndrome (SIDS). An investigation of anaphylactic mechanisms

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Abstract
BackgroundSudden Infant Death Syndrome, (SIDS) or cot death, remains the most common category of post‐perinatal death in the UK. By definition, the cause of death is unknown, but a long‐standing theory is that some of these deaths could be the result of anaphylaxis.ObjectiveTo investigate the potential contribution of anaphylactic mechanisms to deaths in infancy by determining relative levels of α‐ and β‐tryptases and both total and allergen‐specific IgE in sera from groups of infants whose deaths were attributed to SIDS or to other causes.MethodsSerum samples were collected at the time of post‐mortem examination from infants whose death was classed as SIDS (n = 40) and from a comparison group in which cause of death had been established (n = 32). Serum tryptase concentrations were measured with a radioimmunoassay with monoclonal antibody G5 which detects primarily β‐tryptase or an ELISA with antibody AA5 which has equal sensitivity for α‐ and β‐tryptases. Levels of total IgE and IgE specific for casein, β‐lactoglobulin, house dust mite and moulds were determined.ResultsAnalysis of the results of the two assays for tryptase indicated that levels of the β‐like tryptase (the form secreted on anaphylactic degranulation) were significantly higher in serum from infants with SIDS compared with those whose death was explained. There was no evidence for an increase in serum levels of α‐tryptase (the variant secreted constitutively from mast cells). Total levels of serum IgE did not differ between the two groups and, reflecting the low circulating IgE concentrations in infancy, an elevation in IgE specific for the panel of allergens was not detected.ConclusionsIn a proportion of SIDS victims there may be increased serum levels of β‐like tryptase, a marker for anaphylaxis. The failure to detect an increase in α‐tryptase would suggest that mast cell hyperplasia is not a feature of cot death. The nature of the inciting agents remains unclear, but anaphylaxis deserves serious consideration as a possible cause of sudden death in infancy.

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