OR24-06 USP8 Genetic Variants May Contribute to the Development of Bilateral Adrenal Hyperplasia and ACTH-Independent Cushing Syndrome

Abstract

Background: Bilateral adrenocortical hyperplasias (BAHs), including primary pigmented nodular adrenocortical disease (PPNAD), isolated micronodular adrenocortical disease (iMAD) and primary macronodular adrenocortical hyperplasia (PMAH), are rare causes of ACTH-independent Cushing syndrome (CS). PPNAD and iMAD usually present in children or adolescents as multiple small (<1cm), cortisol-producing adrenocortical nodules. On the other hand, PMAH is most frequently identified in older patients with multiple large adrenal nodules. Most patients with PPNAD have PRKAR1A mutations whereas patients with PMAH may harbor variants in other genes (ARMC5, MC2R, GNAS, APC, MEN1). Even though several genes have been associated with ACTH-independent CS, there are still cases that the genetic cause has not been elucidated. Clinical cases: Herein, we present two unrelated patients with ACTH-independent CS that harbor USP8 gene variants. USP8 is mainly known for being mutated in Cushing disease but as a deubiquitinase it may be involved into the Wnt/β-Catenin signaling pathway.The first patient was diagnosed with BAH on prenatal ultrasound (26 gestational week) and subsequently required bilateral adrenalectomy for CS as she had virilization, hirsutism, hypertension and cardiac hypertrophy 9 weeks old. Adrenalectomy revealed that she had iMAD. She also presented with hemihypertrophy of the right leg, labia and mild newborn hypoglycemia, however she was negative for Beckwith-Wiedemann mutation. Gene analysis of PRKAR1A did not reveal any mutations. After whole exome sequencing (WES), we found a novel heterozygous USP8 variant (c.1387_1393delinsT, p.Ala463_Ile465delinsPhe) at germline level and loss of heterozygosity (LOH) at tumor level. Immunohistochemistry showed significantly lower expression of USP8 protein in both of her adrenals compared to a control tissue.The second case is a 59-year old female with osteoporosis who failed to suppress cortisol levels after low dose dexamethasone administration. MRI revealed an adenoma on the right adrenal (2.6cm). She underwent right adrenalectomy and was found to have PMAH. We performed WES in germline level and we detected a novel heterozygous missense USP8 variant (c.287A>G, p.Lys96Arg) that is present also at tumor level. Immunohistochemistry showed significantly lower expression of USP8 protein in her adrenal tumor compared to the control tissue. No LOH was identified. Conclusion: This is the first report of the association of USP8 in ACTH-independent CS and the preliminary findings support UPS8 involvement in the development of adrenocortical disease. We are currently performing further in vitro studies to evaluate the effect of these two USP8 variants into the canonical Wnt pathway which is commonly involved in adrenocortical disorders.