Hemolytic-uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia, and renal failure caused by platelet thrombi in the microcirculation of the kidney and other organs. The onset of atypical HUS (aHUS) ranges from the neonatal period to adulthood. Genetic aHUS accounts for an estimated 60% of all aHUS. Individuals with genetic aHUS frequently experience relapse even after complete recovery following the presenting episode; 60% of genetic aHUS progresses to end-stage renal disease (ESRD).

C1q deficiency (C1QD) is a rare autosomal recessive disorder characterized by recurrent skin lesions, chronic infections, and an increased risk of autoimmune diseases, particularly systemic lupus erythematosus (SLE; see 152700) or SLE-like diseases. It has also been associated with chronic glomerulonephritis and renal failure. C1q deficiency presents in 2 different forms, absent C1q protein or presence of a dysfunctional molecule (summary by Topaloglu et al., 1996 and Vassallo et al., 2007). Genetic Heterogeneity of C1q Deficiency See also C1q deficiency-2 (C1QD2; 620321), caused by mutation in the C1QB gene (120570), and C1q deficiency-3 (C1QD3; 620322), caused by mutation in the C1QC gene (120575).

C3 glomerulopathy (C3G) is a complex ultra-rare complement-mediated renal disease caused by uncontrolled activation of the complement alternative pathway (AP) in the fluid phase (as opposed to cell surface) that is rarely inherited in a simple mendelian fashion. C3G affects individuals of all ages, with a median age at diagnosis of 23 years. Individuals with C3G typically present with hematuria, proteinuria, hematuria and proteinuria, acute nephritic syndrome or nephrotic syndrome, and low levels of the complement component C3. Spontaneous remission of C3G is uncommon, and about half of affected individuals develop end-stage renal disease (ESRD) within ten years of diagnosis, occasionally developing the late comorbidity of impaired visual acuity.