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A Novel GNAS Mutation Causing Isolated Infantile Cushing’s Syndrome

Infantile Cushing’s syndrome is potentially found as part of McCune-Albright syndrome (MAS) which is caused by postzygotic somatic mutations of the GNAS gene. MAS is typically characterized by a triad of polyostotic fibrous dysplasia, café-au-lait skin pigmentation, and precocious puberty or other endocrine hyperfunction. Here, we describe a 2-month-old female infant with features of Cushing’s syndrome without café au lait spots, polyostotic fibrous dysplasia, and clinical evidence of other endocrine hyperfunction. Investigations demonstrated adrenocorticotropic hormone-independent Cushing’s syndrome with bilateral adrenal gland enlargement. Whole-exome sequencing of leukocytes identified a de novo heterozygous novel missense mutation (c.521G>A, p.Cys174Tyr) in the GNAS gene. The patient experienced clinical improvement of Cushing’s syndrome during ketoconazole treatment. Her clinical course was complicated by Pneumocystis jiroveci pneumonia. She also had shortened activated partial thromboplastin time indicating a hypercoagulable state and resulting in pulmonary embolism. She eventually manifested gonadotropin-independent precocious puberty at the age of 13 months after ketoconazole was discontinued. This patient demonstrated that Cushing syndrome can be the presenting sign of MAS in infancy. A high index of suspicion followed by genetic analysis is essential in order to establish a diagnosis.