Cushing syndrome in a pediatric patient with a KCNJ5 variant and successful treatment with low dose ketoconazole.

Context Pathogenic variants in KCNJ5, encoding the GIRK4 (Kir3.4) potassium channel, have been implicated in the pahogenesis of familial hyperaldosteronism (FH) type-III (FH-III) and sporadic primary hyperaldosteronism (PA). In addition to aldosterone, glucocorticoids (GCs) are often found in PA in association with KCNJ5 pathogenic variants, albeit at subclinical levels. However, to date no GIRK4 defects have been linked to Cushing syndrome (CS). Patient We present the case of a 10-year-old child who presented with CS at an early age due to bilateral adrenocortical hyperplasia (BAH). The patient was placed on low-dose ketoconazole (KZL), which controlled hypercortisolemia and CS-related signs. Discontinuation of KZL for even 6 weeks led to recurrent CS. Results Screening for known genes causing cortisol-producing BAHs (PRKAR1A, PRKACA, PRKACB, PDE11A, PDE8B, ARMC5) failed to identify any gene defects. Whole-exome sequencing (WES) showed a novel KCNJ5 pathogenic variant (c.506T>C, p.L169S) inherited from her father. In vitro studies showed that the p.L169S variant affects conductance of the Kir3.4 channel without affecting its expression or membrane localization. Although there were no effects on steroidogenesis in vitro, there were modest changes in protein kinase A activity. In silico analysis of the mutant channel proposed mechanisms for the altered conductance. Conclusions We present a pediatric patient with CS due to BAH and a germline defect in KCNJ5. Molecular investigations of this KCNJ5 variant failed to show a definite cause of her CS. However, this KCNJ5 variant differed in its function from KCNJ5 defects leading to PA. We speculate that GIRK4 (Kir3.4) may play a role in early human adrenocortical development and zonation and participate in the pathogenesis of pediatric BAH.