Systemic lupus erythematosus (SLE) is an autoimmune disease with diverse and variable clinical manifestations and unknown aetiology. Epidemiological and animal studies indicate that environmental and genetic factors are involved in the development of the disease. Several candidate gene loci (including the human leucocyte antigen (HLA) region, Fcγ receptors, and complement components) have been implicated through association studies, and multiple susceptibility loci have been detected in inbred mouse models of SLE.^1,2 Until now, six groups have published genomewide scans with SLE as a phenotype in different ethnic groups.^3–8 Recently, linkage to chromosome 2q37 (logarithm of odds (LOD) 4.24) in a Swedish population resulted in the identification of a new susceptibility gene PDCD1 in a large multinational study by Prokunina et al.^8,9 The SLE associated allele of this immunoreceptor gene alters a binding site for the runt related transcription factor 1 (RUNX1), which is found in an intronic enhancer.

Stratification of pedigrees based on clinical manifestations has been used in recent studies that involved genomewide scans.^10–16 The aim was to achieve genetically and clinically homogeneous sets of families and to increase the power to detect susceptibility genes for different subphenotypes of SLE. Altogether, 17 regions have been linked significantly to SLE with model based and non-parametric approaches; 11 of these in stratified studies. In addition, several other regions with suggestive linkage have been identified, but only some of those loci have been implicated in more than one study.^6,18 The data suggest that multiple genes are involved in conferring susceptibility to SLE.

In our study, we conducted a nationwide and genomewide scan for SLE susceptibility loci in Finnish families multiply affected by SLE. The extensive hospital registration system in Finland allowed us to identify and recruit approximately 85% of all patients with …