NOD2 and ocular melanoma: In this study, expression levels of NOD1 and NOD2 mRNA were compared between 27 otitis-prone patients (i.e., those with a history of OM more than three times in 6 months or four or more times in 1 year) and a non-otitis-prone group of 39 patients (i.e., those with a history of OM 1–2 times every 6 months or three times a year or less).