The rsq1 phenotype was identified in an ENU mutagenesis screen for mutants with impaired response to Toll-like receptor (TLR) ligands. The mutation is a C-to-T transition at nucleotide position 391 of the gene (Genbank Accession NM_133211) resulting in replacement of threonine by isoleucine at amino acid position 68, in the first leucine-rich repeat (LRR) of the receptor.