Complement 4 phenotypes and genotypes in Brazilian patients with classical 21-hydroxylase deficiency

Area of Science:

• Genetics
• Immunology
• Endocrinology

Background:

• 21-hydroxylase deficiency is a common congenital adrenal hyperplasia.
• The C4/CYP21 gene cluster is crucial for steroidogenesis and immune function.
• Understanding C4 gene organization and protein levels is vital for managing this condition.

Purpose of the Study:

• To analyze C4 genotypes, protein levels, and phenotypes in patients with classical 21-hydroxylase deficiency.
• To investigate the correlation between C4 gene organization, protein levels, and clinical manifestations.
• To explore potential associations between C4 haplotypes and recurrent infections or autoimmunity.

Main Methods:

• Molecular analysis of the C4/CYP21 gene cluster using Taq I Southern blotting.
• Genotyping based on gene organization within RCCX modules.
• Quantification of serum C4 isotypes via enzyme-linked immunosorbent assay (ELISA).

Main Results:

• Identified 12 distinct C4/CYP21 gene cluster haplotypes.
• Reduced total functional activity of the classical complement pathway (CH50) observed in 43% of patients due to low C4 concentrations.
• Low C4A or C4B levels correlated with RCCX mono-modular gene organization.

Conclusions:

• C4 gene organization influences C4 protein levels in patients with 21-hydroxylase deficiency.
• No significant association was found between C4 haplotypes and the incidence of recurrent infections or autoimmunity.
• The C4 gene cluster appears evolutionarily protected due to its redundancy.