Case Report: Complement and infection susceptibility

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Diagnosis of complete factor B deficiency

Adapted from: Slade C et al., N Engl J Med, 2013

Case Presentation

A 32-year-old woman with recurrent pneumococcal and meningococcal infection. Clinically significant infections dating from childhood included primary pneumococcal peritonitis at the age of 2 years. Two years later, she was treated for community-acquired pneumonia.

At 15 years of age, she developed meningitis (N. meningitidis, serogroup Y) and at age 30, she suffered from pneumococcal pneumonia complicated by a unilateral empyema.

Evaluation and Diagnosis

Screening tests revealed normal immunoglobulins and lymphocyte subsets. Using the Complement system screen Wieslab® normal classical pathway activity was demonstrated but the alternative pathway was inactive.

Studies showed that the activity of the alternative pathway was restored to the patient’s serum by properdin-deficient serum but not with factor B-depleted serum. Factor B was undetectable by means of radial immunodiffusion and ELISA indicating complete factor B deficiency.

Genome sequencing of the factor B gene revealed compound heterozygous mutations. These mutations were also identified in the mother and father, respectively. The patient received tetravalent meningococcal vaccine, 23-valent pneumococcal polysaccharide vaccine, as well as continuous prophylactic amoxicillin, and she has not had any further severe infections.

Discussion and Conclusion

In cases with meningococcal disease the possibility of a complement deficiency has to be considered, especially deficiencies affecting the alternative pathway.

Several cases with properdin deficiency and a few with factor D deficiency are previously described, but this is, to our knowledge, the first case report of complete factor B deficiency. The findings confirm the crucial role of the alternative complement pathway in protection against infection by organisms causing meningitis.

This case clearly demonstrates the usefulness of functional assays for screening of complement deficiencies. The use of such tests means that more deficiency cases can be found and thus also that appropriate treatment can be given to the deficient individuals and when needed their family members.

 



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