The causal link between inherited complement deficiencies and systemic lupus erythematosus
(SLE) has been well established, although it remains a rare cause of the disease. We present the
case of three biological sisters with hereditary heterozygous C2 deficiency, but who differ widely in
their clinical and serological manifestations. Patient 1 is 25 years old and was diagnosed with SLE at
the age of 12. Further testing revealed positive ANA and anti-dsDNA, antiphospholipid syndrome
(APS) and decreased C2, C3 and C4 levels. Patients 2 and 3 are 21-year-old dizygotic twins. Both
have positive ANA and antiphospholipid (APL) antibodies, and decreased C2 and C4 levels. We
present a case of familial heterozygous C2 deficiency with different disease phenotypes. The presence
of positive APL antibodies in all 3 patients is significant, as this association has been rarely
described. The variable clinical and serological manifestations among our patients further reflect the
complex and multifactorial nature of SLE.
Keywords: Systemic lupus erythematosus, complement deficiency, autoimmune disorders, antiphospholipid syndrome.
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