Case Report: Complement and infection susceptibility

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Diagnosis of properdin deficiency

Adapted from: Genel et al., Acta Paediatr., 2007

Case Presentation

A 5½-year-old boy of non-consanguineous parents was admitted to our hospital with meningococcal septic shock. He had previously been suffering from recurrent respiratory infections. His 13-year-old brother had also been treated for meningococcal meningitis when he was 7 years old. A 19-year old brother was healthy.

Evaluation and Diagnosis

Immunological studies, done after recovery, on the patient and his two brothers revealed normal immunoglobulins, IgG subclasses, C3, C4 and classical pathway activity while activity of the alternative complement pathway could not be detected. Further analysis revealed a properdin concentration of <0.01 mg/L while factor D was 50% of the normal and factor B 97% of the normal. These findings confirmed the suspected diagnosis of properdin deficiency. The concentration of complement proteins were also studied in the family members. The two brothers of the patient were also properdin-deficient and the mother had a reduced properdin level which is seen in most female properdin deficiency carriers.

Discussion and Conclusion

Properdin deficiency is associated with highly increased risk for Neisserial infections. The gene for properdin is located on the X-chromosome and therefore male individuals are affected. It is important to study family members to find other who also may have the same deficiency. Deficient individuals are given prophylaxis by vaccination against meningococci. Awareness of the increased risk is also important to ensure proper antibiotic therapy when needed. Analysis of complement function with the Complement system screen Wieslab® is an excellent assay for detection of all types of alternative pathway deficiencies.

 

Diagnosis of properdin deficiency

Adapted from: Helminen et al., Scand J Immunol. 2012

Case Presentation

The patient was a previously healthy boy, aged 14 years who was suspected to have meningococcal infection based on fever and skin symptoms. Preceding hospital care the patient had vomiting, loose stools and worsening arthralgia on his wrists and ankles.

Laboratory investigations revealed leucocytosis and highly increased CRP level. Since the clinical picture seemed to indicate meningococcal infection i.v. penicillin therapy was started.

Evaluation and Diagnosis

Serology showed normal immunoglobulin and tetanus antibody levels. The C3 level was normal but C4 level subnormal.

When analyzing with the Complement system screen Wieslab® test, the functional activity of the classical pathway was normal but the functional activities of the alternative and lectin pathways were undetectable. Subsequent analysis showed no properdin protein and sequencing of the properdin gene confirmed properdin deficiency.

A mutation in exon 9 of the properdin gene at codon 388, where tryptophan was changed to a premature stop codon (W388X), was identified.

Discussion and Conclusion

In cases with meningococcal disease the possibility of complement deficiency has to be considered. Particularly deficiencies affecting the alternative pathway are important and properdin deficiency is associated with highly increased risk for Neisserial infections.

The gene for properdin is located on the X-chromosome, i.e. male individuals are affected and family members should be investigated. Prophylaxis by vaccination using tetravalent meningococcal vaccine may prevent additional life-threatening infections in family members with properdin deficiency. This was the first case in a family in Finland where a mutation in the properdin gene was reported.

The Complement system screen Wieslab® is an useful assay suited for detection of all types of alternative pathway deficiencies.

 

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