CDKN1B and multiple endocrine neoplasia type 4: Based on the underlying genetic defect, there are various syndromes, such as multiple endocrine neoplasia type 1 (MEN1) caused by pathogenic variants of MEN1 gene, multiple endocrine neoplasia type 2 (MEN2) due to pathogenic variants of RET oncogene, multiple endocrine neoplasia type 4 (MEN4) harboring CDKN1B/p27 defects, hyperparathyroidism-jaw tumor syndrome due to pathogenic variants of CDC73 gene, as well as familial isolated primary hyperparathyroidism [8,9,10,11,12].