SUN-291 Presence of Aberrant Adrenocorticotropic Hormone Precursors in Two Cases of McCune- Albright Syndrome

Background: McCune-Albright syndrome (MAS) is a rare disorder. MAS is caused by an activating postzygotic somatic mutation in the GNAS, and, is classically defined by the occurrence of fibrous dysplasia (FD), café-au-lait skin macules, and precocious puberty. Autonomous GH and/or PRL production in MAS has been reported. However, there have been no reports of ACTH excess in MAS. Method: Plasma ACTH and serum cortisol (F) levels were assessed using electrochemiluminescence immunoassays (Eclusys ACTH(TM) and Eclusys Cortisol II(TM), respectively; Roche Diagnostics K.K., Tokyo, Japan).Clinical Cases: Case1; 42-year-old man showed craniofacial deformities and suffered from multiple bone fractures. He was diagnosed with FD at the age of 23 years. Café-au-lait macules were found on his back. He had slightly acromegaloid features. He showed no cushingoid features. Pituitary adenoma or hyperplasia was not detected by MRI. The diagnosis of GH excess was confirmed by no suppression of serum GH levels by a 75-g oral glucose tolerance test (nadir GH: 2.34 ng/mL) and an elevated serum IGF-I level (307 ng/mL; normal range: 92-257 ng/mL). The patient was treated with monthly subcutaneous lanreotide injection and then GH excess was well controlled. Basal ACTH and F levels in blood were 40.6-63.4 pg/mL and 8.0-10.5 μg/dL, respectively. The urinary free cortisol (UFC) level was 53 μg/day. Autonomous F excess was excluded by the level of midnight F (1.2 μg/dL) and the level of F (0.2 μg/dL) after a low-dose (1 mg) dexamethasone suppression test (DST). Case2; A 32-year-old man was diagnosed with MAS and gigantism at the Pediatrics Department at the age of 5 years. Treatment of GH excess was well controlled by monthly octreotide depot. He had no acromegaloid features and no cushingoid features. Café-au-lait macules were observed from the left flank to the back. Pituitary adenoma or hyperplasia was not detected by MRI. Basal ACTH and F levels in blood were 35.5-73.1 pg/mL and 7.0-11.7 μg/dL, respectively. The UFC level was 61 μg/day. Autonomous F excess was excluded by the level of F (<0.2 μg/dL) after a low-dose (0.5 mg) DST.Possibility of primary adrenal insufficiency was excluded by ACTH stimulation test and/or insulin tolerance test in both cases. The involvement of 11β-HSD1 by GH excess and PC1/3 deficiency were also excluded. Gel exclusion chromatography was then performed. POMC and pro-ACTH were detected and the aberrant ACTH/normal ACTH ratio was 42% in both cases. Conclusion: This is the first report of the presence of aberrant ACTH precursors, particularly POMC, in MAS. A high ratio of circulating ACTH to F may suggest secretion of inactive ACTH precursors in MAS. Further investigations are required to determine whether GNAS mutations or other mechanisms are involved in the presence of aberrant ACTH precursors in MAS.