Quantitative RT-PCR analysis of the 39 HOX genes by an earlier study showed upregulation of 23 HOX genes among familial MEN1 parathyroid tumors with biallelic MEN1 loss, and downregulation of 5 HOX genes among sporadic parathyroid tumors without MEN1 loss [17]. This evidence concerns the gene MEN1 and multiple endocrine neoplasia type 1.