A genetic marker within the CD44 gene confirms linkage at 11p13 in African-American families with lupus stratified by thrombocytopenia, but genetic association with CD44 is not present.

Systemic lupus erythematosus (SLE) is complicated from both a clinical and genetic standpoint. We have stratified SLE families by the presence of thrombocytopenia, which is associated with increased mortality among SLE patients, and found genetic linkage at chromosome 11p13 in African-American families. In the present study we have evaluated CD44, a gene very close (0.5 cM) to the peak LOD score marker, as a candidate gene. Using a newly identified short DNA repeat within the CD44 gene, we find a LOD score of 2.7, which confirms linkage within this genetic interval. However, using a panel of four single nucleotide markers spanning the CD44 gene, we find no genetic association with SLE. Therefore, these data further suggest an SLE susceptibility gene at 11p13, but also imply that an ancestral mutation in the CD44 gene does not account for the linkage.