12504 Update On Aldosterone-producing Micronodules: Somatic Mutations And RNA Expression Profiles

Abstract Disclosure: C. Wu: None. J. Lim: None. A. Blinder: None. W.E. Rainey: None. A. Udager: None. Background: Primary aldosteronism (PA) is the leading cause of endocrine hypertension and results from either bilateral or unilateral adrenal disease. Most unilateral PA is caused by aldosterone-producing adenomas (APA). In contrast, many bilateral cases have aldosterone-producing micronodules (APM); defined as aldosterone synthase (CYP11B2)-positive lesions ≤10 mm in size located under the adrenal capsule. Both APA and APM have been found to have aldosterone-driver mutations. Objective: To characterize somatic mutation and RNA expression patterns in APM from PA and renal donor adrenals. Methods: Sixty-five APM from renal donors were compared with 102 APM from PA patients who underwent adrenalectomy at the University of Michigan. Immunohistochemistry for CYP11B2 localized APM, which were captured from serial sections, used for DNA and RNA isolation, and then targeted next-generation sequencing (NGS). Results: From renal donor adrenals, 51 APM passed NGS quality control criteria. 45.1% of the APM harbored an aldosterone-driver mutation. Mutations were observed in CACNA1D (n=21; 41.2%) and ATP2B3 (n=2; 3.9%). The remainder were negative for known mutations (n=28; 54.9%). From PA adrenals, 76 APM passed NGS quality control criteria. Aldosterone-driver mutations were found in 67.1%, which was significantly higher than donor adrenals (p-value=0.017). Although CACNA1D mutations were still dominant in PA adrenals (n=44; 57.9%), 25 (32.9%) APM remained negative for known aldosterone-driver mutations. Other PA adrenal-detected mutations included CACNA1H (n=3; 3.9%), KCNJ5 (n=2; 2.6%), ATP1A1 (n=1; 1.3%), and CADM1 (n=1; 1.3%). Gene expression analyses were performed for 19 renal donor APM and 14 PA adrenal APM using principal component analysis (PCA) and unsupervised hierarchical clustering using targeted RNAseq data from adrenal cortical tumors [APA (n=8), cortisol-producing adenomas (CPA; n=11), and adrenal cortical carcinomas (ACC; n=8)] and adrenal cortical zones [zona glomerulosa (ZG; n=8), zona fasciculata (ZF; n=4), and zona reticularis (ZF; n=5)]. APM samples demonstrated similar gene expression patterns to and clustered with ZG and APA samples in heatmaps and PCA plots. Differential expression analysis revealed a subset of genes with higher expression in APM from renal donor adrenals compared to APM from PA adrenals and APA, including several negative regulators of WNT signaling (DKK3, NKD1, and ZNRF3). Conclusions: APM bearing aldosterone-driver mutations are present in adrenals from both renal donors and PA patients. The majority of APM had somatic mutations known to cause PA. CACNA1D mutations were most common, but the genetic cause of many APM remains unknown. RNAseq analysis suggest APM are most closely related to the APA and normal glomerulosa. Additional research is needed to define the contribution of APM to unilateral and bilateral PA. Presentation: 6/3/2024