Case Report: Complement and infection susceptibility
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Diagnosis of C1q deficiency
Adapted from: Genel et al., J Investig Allergol Clin Immunol., 2010
This case was an 11-year-old girl who was admitted with fever and loss of consciousness. Her medical history included bacterial meningitis at the age of 8 and pneumonia at the age of 10. The parents were first-degree cousins.
Evaluation and Diagnosis
Meningitis caused by Streptococcus pneumoniae was diagnosed and antibiotics were administered. The patient was then vaccinated against meningococci, pneumococci, and Haemophilus influenzae type B, and penicillin prophylaxis was administered. Her antinuclear antibody and rheumatoid factor titers were negative after repeated investigations. During a 5-year follow-up, she was asymptomatic for autoimmune diseases and infections.
Immunologic studies performed when the patient had recovered revealed normal immunoglobulin levels. Alternative pathway complement activity was normal, but no classical pathway activity was detected. Levels of complement proteins C2, C3, and C4 were within normal ranges. The serum concentration of C1q was below the detection limit and further analysis led to the diagnosis of C1q deficiency. The parents and 5 siblings, who were well and had no history to suggest increased susceptibility to infection, all had normal classical and alternative pathway function, as well as normal C3 and C4 concentrations. However, in 4 of the siblings the serum concentrations of C1q were below the normal range.
Subsequent genetic analysis revealed a homozygous missense mutation in the C1q C gene causing a substitution affecting the collagen-like region of C1q and thus explaining the deficiency.
Discussion and Conclusion
C1q deficiency is a rare but in many cases very serious deficiency although this varies between patients. The deficiency is associated with both SLE-like disease which about 90% suffer from and infections as was predominant in this case. Since there is a great variation in the symptoms treatment must be individualized. The C1q molecules are produced in myeloid cells and therefore hematopoietic stem cell transplantation has been tried in a few cases. When symptoms suggesting SLE is present an initial analysis of complement function and not only C3 and C4 is needed to not overlook this deficiency.