Research published over the last eight years has established that somatic defects in codons 718–720 of USP8 (exon 14 in NM_005154.5) are the most frequent genetic cause of CD, being found in 21–62% of corticotropinomas [11,12,43,182,183,184,185,186,187,188,189,190,191,192,193,194,195]. Here, USP8 is linked to ACTH-producing pituitary gland adenoma.