LAUSR

BACKGROUND Somatic variants in KCNJ5 are the most common cause of primary aldosteronism (PA). There are few patients with PA in whom the disease is caused by germline variants in the KCNJ5 pottasium channel gene (familial hyperaldosteronism type III - FH-III). METHODS A 5 year-old patient who developed hypertension due to bilateral adrenocortical hyperplasia (BAH) causing PA had negative peripheral DNA testing for any known genetic causes of PA. He was treated medically with adequate control of his PA but by the third decade of his life, due to worsening renal function, he underwent bilateral adrenalectomy. RESULTS Focused exome sequencing in multiple nodules of his BAH uncovered a "hot-spot" pathogenic KCNJ5 variant, while repeated Sanger sequencing showed no detectable DNA defects in peripheral blood and other tissues. However, whole exome, "deep" sequencing revealed that 0.23% of copies of germline DNA did in fact carry the same KCNJ5 variant that was present in the adrenocortical nodules, suggesting low level germline mosaicism for this PA-causing KCNJ5 defect. CONCLUSIONS Thus, this patient represents the first to our knowledge case of BAH due to a mosaic KCNJ5 defect. Undoubtedly, his milder PA compared to other known cases of FH-III, was due to his mosaicism. This case has a number of implications for the prognosis, treatment and counseling of the many patients with PA due to BAH that are seen in hypertension clinics.