Few large, multi-ethnic studies have examined the clinical and serologic differences between familial and sporadic SLE patients. Understanding these similarities and differences is critical for interpreting genetic studies and developing therapeutic strategies. We compiled information on 1915 patients with SLE in a large multi-racial cohort, including general demographics, pedigree structure and the specific American College of Rheumatology (ACR) criteria met. One patient was randomly selected from each multiplex family for analysis, yielding 554 European-Americans (EA), 373 African-Americans (AA), 193 Hispanics (HI) and 237 patients of other of mixed races. When comparing familial and sporadic patients stratified by race, lupus erythematosus (LE) cells and arthritis were increased in white familial cases (P = 5.5 x 10(-6) and P = 0.028, respectively), but no other significant differences between familial and sporadic patients were found. We found that there were profound differences in clinical profiles between races. For example, photosensitivity and malar rash were decreased in AA (P = 1.3 x 10(-13) and 1.4 x 10(-7), respectively), whereas discoid rash was increased in AA (P = 5.5x10(-6)). EA had significantly less renal disease (P = 5.4x10(-13)), proteinuria (P = 4 x 10(-12)) and anti-Sm (P = 1.7 x 10(-12)) than AA or HI. We, therefore, conclude that familial and sporadic onset patients may be treated similarly with respect to clinical and genetic studies.

Systemic lupus erythematosus (SLE) is a prototype systemic, autoimmune inflammatory disease that can involve virtually any organ or tissue type. The disease has a strong familial tendency but, like most human illness, has a complex pattern of inheritance that is consistent with multiple susceptibility genes as well as environmental risk factors. Association studies have been performed, especially for the major histocompatibility complex on chromosome 6 and for various complement components. Several large familial studies have begun to report results for genetic linkage. Linkage has been established for many genetic intervals. SLE is a complex clinical illness, and investigation of the genetics of the illness based on clinical manifestations revealed linkages not found without consideration of the phenotype of the disease.

We detected a novel susceptibility gene, SLER1, for systemic lupus erythematosus (SLE) at 5p15.3. 1 This finding was based on a selected subgroup of SLE families, where two or more family members have had alleged rheumatoid arthritis (SLE-RA). The main objective of this study was to replicate the linkage at 5p15.3 based on an independent data set of 88 SLE-RA families. Heterogeneity in the genetic model led us to use a nonparametric allele-sharing method. Since our a priori hypothesis of linkage at 5p15.3 was fixed, we genotyped six markers at the linked region. Our new results replicate the initial linkage at 5p15.3 (Zlr ¼ 2.58, Po0.005, LOD ¼ 1.45). Moreover, evidence of linkage was sustained when analysis was restricted to the subset of SLE families who had 3 or more individuals with alleged RA (Zlr ¼ 3.32, P ¼ 0.008, LOD ¼ 2.40) The results of our previous findings, together with these new results, confirm the SLER1 linkage at 5p15.3. Our results also demonstrate the utility of clinically defined subgroup analysis for detecting susceptibility loci for complex genetic diseases, such as SLE.