Cyclin D1 (also located at 11q13) is overexpressed in 10–40% of parathyroid adenomas due to aberrant promoter methylation of different cyclin-dependent kinase inhibitors (CDKIs), while rearrangement of the Cyclin D1 gene (CCND1) occurs in up to ~ 10% of parathyroid adenomas [105]. This evidence concerns the gene CCND1 and parathyroid gland adenoma.