CDKN1B and tumor of parathyroid gland: Thus, Cdkn1b+/− mice develop tumours consistent with MEN4, which is characterised by the occurrence of pituitary and parathyroid tumours in association with other endocrine tumours (e.g. of gonads and adrenals) (Kiyokawa et al., 1996, Nakayama et al., 1996, Fero et al., 1998).