[A congenital deficiency of the C3 fraction of complement. A familial study]
Fayçal Sassi1, Mohamed Bejaoui, Khaled Ayed
1Centre de greffe de moelle, Tunis.
Insights
A rare complement C3 deficit caused recurrent infections and developmental delay in a child. Supplementing functional C3 restored immune activity, confirming the diagnosis in this case study.
Area of Science:
- Immunology
- Genetics
Background:
- The complement system is crucial for innate and adaptive immunity.
- Deficiencies in complement components, particularly C3, are rare and linked to increased infection susceptibility.
- Clinical presentation of complement deficiencies can mimic other immune disorders.
Observation:
- A 6-year-old child presented with psychomotor delay and recurrent infections.
- Immunochemical analysis revealed a complete absence of complement C3 and C3d in the child's serum.
- Both classic and alternative complement pathways showed significantly reduced hemolytic activity.
Findings:
- Functional C3 addition to the patient's serum restored global hemolytic activity in a dose-dependent manner.
- Parents exhibited approximately 50% reduced C3 levels and global hemolytic activity, indicating an autosomal recessive inheritance pattern.
- Normal Factor I levels in the family ruled out Factor I deficiency as the cause.
Implications:
- This case highlights the critical role of complement C3 in immune defense.
- Early diagnosis of C3 deficiency is essential for managing recurrent infections and potential developmental issues.
- Understanding complement component deficiencies aids in genetic counseling and therapeutic strategies.
Abstract:
The innate deficit of the third constituent of the complement is extremely rare, it appears clinically as a deficit of the humorale immunity. We report a case of C3 deficit in a 6 year old Tunisian child, who presents a psychomotor delay and recurrent infections. The investigation of the complement system profile by an immunochemical test of the children's serum shows an absence of C3 and C3d, associated to a loss of classic and alternate hemolytic pathway activities. The addition of functional C3 in the deficient serum restores the global hemolytic activity. The reconstruction of the hemolytic activity is dose dependent of C3 added quantity. The rate of C3 is lowered in the parent's with a 50% decrease of the global hemolytic activity. Immunochemical measurement of C3d confirms the absence of any C3 catabolism product in vivo. On the other hand (factor I) show a normal rate to all the family members.
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