Impact of Homozygous C4A Deficiency on Clinical Presentation of Systemic Lupus Erythematosus.

Objective: To investigate the association of C4A null allele (C4AQ0) with systemic lupus erythematosus (SLE) and determine the clinical presentation of SLE in relation to C4A null allele.

Study Design: Descriptive study.

Place And Duration Of Study: Armed Forces Institute of Pathology (AFIP), Rawalpindi, Immunology Department, from December 2018 to December 2019.

Methodology: Patients referred to AFIP, who fulfilled American College of Rheumatology (ACR) criteria of 1997 for diagnosis of SLE were included in the study. Approval from the Institutional Ethical Review Board was taken. C4A and C4B null alleles were determined in 66 SLE patients and 40 age- and gender-matched healthy controls by polymerase chain reaction (PCR) using sequence-specific primers (PCR-SSP). Various clinical features and laboratory findings in the SLE patients were analysed in relation with C4A null allele.

Results: The mean age of the study population was 30.56 ±10.08 years. C4A null allele was detected in 7 (10.6%) patients; whereas, C4B null allele was detected in only two (3%) patients. SLE patients with C4A null allele had increased incidence of arthritis (100%) and renal damage (85.7%); compared to those with normal C4A allele, 57.6% and 32%, respectively. Fisher's Exact test revealed strong association of C4A null allele with arthritis and renal damage, (p = 0.039 and 0.01, respectively).

Conclusion: Homozygous absence of C4A alleles was encountered in 10.6% of Pakistani patients of SLE and is closely related with clinical features of arthritis and renal damage. Knowledge of C4A null allele in SLE patients at diagnosis can predict disease course. Key Words: SLE, C4A null alleles, C4AQ0, Homozygous C4A deficiency.