Cyclin D1 protein overexpression occurs in 20–40% of parathyroid adenomas, suggesting that increased PRAD1/cyclin D1 is one of the genetic abnormalities responsible for tumorigenesis in sporadic primary parathyroid adenomas, contributing to parathyroid hyperplasia in humans [110,111,112]. Here, CCND1 is linked to parathyroid hyperplasia.