Bilateral adrenal macronodular hyperplasia (BMAH) is a rare form of Cushing's syndrome characterised by the presence of bilateral secretory adrenal nodules and hypercortisolism. Familial studies support a genetic basis for BMAH, and the disease has been linked to mutations in ARMC5, a gene shown to have a tumour suppressor-like action in the development of adrenal nodules. This study aimed to investigate whether ARMC5 mutations play a role in the development of incidentally discovered bilateral adrenal nodules. We investigated 39 patients with incidentally discovered bilateral adrenal nodules >0.8 cm in diameter who underwent extensive biochemical testing to look for signs of subclinical hypercortisolism. Genomic DNA was analysed by Sanger sequencing, using primers targeted to ARMC5 transcripts. Of the 39 patients included in our study, three were identified as having variants in ARMC5. Two of these are unlikely to be clinically significant, but there is evidence that the third mutation, Chr16:g.31476122;c.1778G>C (p.Arg593Pro), may be pathogenic. Another variant, affecting the same amino-acid residue c.1777C>T (p.Arg593Trp), has been identified previously in two studies of BMAH patients, where it has been shown to segregate with disease in one BMAH family. This patient had biochemical evidence of hypercortisolism in the absence of overt Cushing's syndrome, and underwent bilateral adrenalectomy separated in time. The presence of a probably clinically significant mutation in ARMC5 in one patient with bilateral adrenal incidentalomas adds to the growing body of evidence in support of ARMC5 as a critical mediator of adrenal nodule development. In addition, the absence of significant ARMC5 mutations in 38 of our patients represents an important negative finding, demonstrating the degree of variability within the pathogenesis of adrenal nodule development.
Keywords: ARMC5; Adrenal hyperplasia; Adrenal incidentalomas; Adrenal nodule; Cushing’s syndrome.