Interestingly, of the four coding variants found solely in IP patients, a three-locus haplotype (G-A-G) including the rs28366003 SNP variant allele of the MT2A gene was found to be significantly associated with a 16 % increased risk of inverted papilloma (OR = 1.16; 95 % CI, 0.74–1.94, pglobal = 0.02). This evidence concerns the gene MT2A and incontinentia pigmenti.