Given the abovementioned strain- and species-specific differences in tissue tropism among Lyme disease spirochetes, an attractive hypothesis is that the decorin and/or GAG-binding activities of DbpA (and DbpB) are critical for promoting colonization, and that allelic variation of dbpA might influence the tissue tropism of Lyme disease spirochetes. The gene discussed is YBX1; the disease is Lyme disease.