Lupus Nephritis – Genetic Impact on Clinical Phenotypes, Disease Severity and Renal Outcome

Abstract: Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease that can affect every organ system. Lupus nephritis (LN) is one of the more serious SLE manifestations. Whilst the genetic background of SLE has been thoroughly investigated, less is known about the background of LN. The aim of this thesis was to further elucidate the genetic background of LN, its subtypes and outcome.In paper I, we analysed genetic variations for association with LN, its severe form proliferative nephritis and renal outcome, in two SLE cohorts. Patients and controls were genotyped and association analyses were performed for patients versus controls and for patients with or without a specific clinical manifestation. In the case-control analysis of cohort I, four highly linked risk alleles in the STAT4 gene were associated with LN with genome-wide significance. In the case-only meta-analysis of the two cohorts, a STAT4 risk allele was associated with severe renal insufficiency. We conclude that genetic variations in STAT4 predispose to LN and a worse outcome with severe renal insufficiency.In paper II, we describe a case of severe SLE on the basis of C1q deficiency. By sequencing, a mutation in the C1qC gene leading to a premature stop codon was found. The patient was also found to carry risk alleles in several SLE-associated variants. Interferon alpha (IFN-α) levels were analysed over time in patient serum, and were found to correlate with disease activity. The patient’s serum had a strong interferogenic capacity when stimulating peripheral blood mononuclear cells from healthy individuals. With this study, we further emphasise the role of IFN-α in C1q deficiency and highlight the need to consider inherited impairments in the complement system in SLE with childhood onset.In paper III, we studied the impact of sex on disease manifestations in SLE. Female SLE patients more often presented with malar rash, photosensitivity, oral ulcers and arthritis, whilst the frequency of serositis, renal disorder and immunologic disorder were higher among male patients. Women were younger at LN onset, whereas men had a higher risk for progression into end-stage renal disease.In paper IV, we analysed genetic variations for association with LN and its subtypes in three SLE cohorts. Patients were genotyped and association analyses were performed for patients with versus without different phenotypes. We found genetic variations in the BANK1 gene to be associated with LN.In conclusion, this thesis provides further insight into the genetic background of renal manifestations in patients with SLE.