Hereditary Heterozygous C2 Deficiency: Variable Clinical and Serological Manifestations Among Three Sisters

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.