Homozygous C2 deficiency with fulminant lupus erythematosus: severe nephritis via the alternative complement pathway

Rare autoimmune disorders with Mendelian inheritance

Autoimmune diseases represent a heterogeneous group of common disorders defined by complex trait genetics and environmental effects. The genetic variants usually align in immune and metabolic pathways that affect cell survival or apoptosis and modulate leukocyte function. Nevertheless, the exact triggers of disease development remain poorly understood and the current therapeutic interventions only modify the disease course. Both the prevention and the cure of autoimmune disorders are beyond our present medical capabilities. In contrast, a growing number of single gene autoimmune disorders have also been identified and characterized in the last few decades. Mutations and other gene alterations exert significant effects in these conditions, and often affect genes involved in central or peripheral immunologic tolerance induction. Even though a single genetic abnormality may be the disease trigger, it usually upsets a number of interactions among immune cells, and the biological developments of these monogenic disorders are also complex. Nevertheless, identification of the triggering molecular abnormalities greatly contributes to our understanding of the pathogenesis of autoimmunity and facilitates the development of newer and more effective treatment strategies.

Systemic lupus erythematosus in childhood

Systemic lupus erythematosus is a disease of immune dysregulation that strikes approximately 1 in 2000 individuals. The usual patient is a young woman of child-bearing age; however, this illness affects patients of all ages, ethnic backgrounds, and both sexes. Twenty percent of all cases of lupus are diagnosed during the first two decades of life. Perhaps the most essential point in treating a child with lupus is to be aware and concerned about how to deliver treatment to a patient in the middle of their physical, intellectual, and emotional development.

Sex influences transmission of the supratype associated with the C2 deficiency allele: a possible mechanism for the maintenance of heterozygosity and disease susceptibility

We have examined the transmission of the supratype associated with C2 deficiency (C2Q0) using our own and many published pedigrees in order to determine whether nonrandom transmission may contribute to the stability of disease-associated supratypes. Unexpectedly, we found that C2Q0 may be preferentially transmitted to the opposite sex and therefore propose that such "zig-zag" transmission may result in the preservation of recessive disease susceptibility genes and in the maintenance of heterozygosity. Further pedigrees are required to verify our findings.

Sequential studies of complement activation in systemic lupus erythematosus

C1 and C3 activation, measured as C1r-C1s-C1 inactivator C1s-C1r-C1IA complexes in serum and circulating C3d were studied in serial samples from 33 patients with SLE. All patients demonstrated exacerbations during observation periods of 10-30 months and were divided into groups according to principal clincal features (mild SLE, severe extra-renal SLE, and lupus glomerulonephritis). Increased C1 activation was consistently found during exacerbation. C3d in plasma was a feature associated with severe disease flares. Activation of C1, but not of C3, was documented before flare-ups of disease activity, but such predictive information was mostly restricted to patients with extra-renal disease. C2 cleavage in plasma, studied serially in a few patients, appeared to be closely associated with C1 activation. Circulating immune complexes, measured with solid-phase C1q assay, did not always increase before development of clinical manifestations. Remission of symptoms was paralleled by decreasing concentrations of C1r-C1s-C1IA and of, when present, C3d. Similar findings were made for immune complexes but only in severe disease. Persisting C3d was observed in 3 patients, who subsequently developed renal failure. C1q levels were transiently low during flare-ups of lupus glomerulonephritis, but otherwise the concentrations of C1q, C4 and C3 did not show consistent patterns of variation in relation to disease activity.

Inherited disorders of complement

Isolated complement component deficiencies are uncommon. Deficiencies of all eleven components and two inhibitors of the classical pathway have been described. Complete absence of the components of the alternative pathway has not been described. The consequences of a single defect in complement are often predictable from an understanding of the biologic activities associated with activation of the complement system. Deficiency of C1 esterase inhibitor gives rise to the disease, hereditary angioedema; deficiency of the early components of the classical pathway are associated with lupus erythematosus; C3 and C3 inactivator deficiencies with pyogenic infections; C5 dysfunction with Leiner's disease; deficiencies of the terminal components with recurrent Neisseria bacteremia; and C9 deficiency with normal health. The complement system and its associated biologic activities are reviewed. The present knowledge of the inherited complement deficiencies and associated diseases, with particular emphasis on the dermatologic manifestations, genetics, and diagnosis, is summarized.

Recurrent pyogenic infections in individuals with absence of the second component of complement

While deficiency of the terminal components of complement (C3-C8) has classically been associated with recurrent pyogenic infections, it has become apparent that C2 deficiency is also associated with recurrent infections in some individuals. The patient presented here had two major pyogenic infections prior to 1 year of age and was found to lack the second component of complement. Studies of alternative complement pathway and humoral and cellular immunity were found to be within normal limits. Family studies suggest an autosomal codominant pattern of inheritance for the C2 defect, which also corresponded to the inheritance of the HLA A10 B18 haplotype. A review of the literature revealed nine other cases of C2-deficient patients with well-documented recurrent infections. In these patients, Streptococcus pneumoniae is the organism most frequently implicated in infectious processes, whether or not their alternative complement pathway is intact.

Lupus erythematosus

Lupus erythematosus (LE) is a multisystem disease. Genetic predisposition, altered immunity, hormones, drugs, viruses, and ultraviolet light all may play a role in etiology. A wide range of cutaneous lesions occur, and variants such as subacute cutaneous LE, complement-deficient LE, and neonatal LE have recently been emphasized. Management of the LE patient, including appropriate diagnostic studies and therapy relevant to the dermatologist, is discussed in the review.

A hypocomplementemic vasculitic urticarial syndrome. Report of four new cases and definition of the disease

We describe four new patients with a unique syndrome of persistent urticaria, with leukoclastic angiitis, severe angioedema, occasional life-threatening laryngeal edema, arthritis, arthralgia, neurologic abnormalities and pronounced persistent hypocomplementemia. The complement abnormalities involved markedly reduced levels of the Clq subunit of the first component of complement (Cl) in the presence of near normal levels of Clr and Cls subunits of Cl; modest to marked depletion of the fourth component of complement (C4), the second component of complement (C2) and the third component of complement (C3); and normal levels of the fifth through ninth components of complement (C5 through C9) and properdin factors B and D. A striking serologic abnormality found in all patients was the presence of low molecular weight (7S) proteins which precipitated with Clq in agarose gels; these previously were shown to be comprised at least in part of immunoglobulin G. The present experience is offered to help to define the clinical, histopathologic and serologic characteristics of this entity, designated hypocomplementemic vasculitic urticarial syndrome, and to emphasize its distinctiveness and prevalence.

Polymorphism of the second component of human complement (C2). Observation of the rare phenotype (C2 2 (= C2 B) and data on the localization of the C2 locus in the HLA region

The polymorphism of the second component of human complement was studied by means of isoelectric focusing in polyacrylamide gels with subsequent complement-dependent lysis of sensitized sheep erythrocytes in an agarose overlay containing C2-deficient or normal human serum. In a material of 289 unrelated individuals the following gene frequencies were observed: C21=0.965 and C22=0.035. The rare phenotype C2 2 (=C2 B) could be seen once in a child of a C2 1--2 heterozygous mother. The investigation of the C2/HLA relationship revealed a very close linkage: Among 62 informative meiotic divisions one recombination between HLA-B and C2 was found (i.e. 1.61%); in addition, C2(2) was significantly associated with HLA-B15 and -Cw3. In a family with an HLA-B/D(DR) crossover C2 segregated together with HLA-D(DR). This supports the assumption of a C2 structural locus outside HLA-B, probably near HLA-D(DR).