Context: Primary macronodular adrenal hyperplasia (PMAH) is a rare type of Cushing or subclinical Cushing syndrome and is associated with bilateral multinodular formation. ARMC5 is one of the responsible genes for PMAH. Objectives: This study was performed to identify the genotype-phenotype correlation of ARMC5 in a cohort of Japanese patients. Patients and Methods: Fourteen patients with clinically diagnosed PMAH and family members of selected patients were studied for ARMC5 gene alteration and clinical phenotype. The associated nonadrenal tumor tissues were also studied. Results: Of fourteen patients with PMAH, 10 had pathogenic or likely pathogenic variants of ARMC5. We found two variants. Five unrelated patients had identical variants (p.R619∗). In two patients, the variant was found in offspring with the asymptomatic or presymptomatic state. Six of ten patients who tested positive for the ARMC5 pathogenic or likely pathogenic variant carried nonadrenal tumors; however, no loss of heterozygosity (LOH) or second hit of the ARMC5 gene was evident. The ARMC5 variant-positive group showed a significantly higher basal cortisol level. Furthermore, age-dependent cortisol hypersecretion was seen in the ARMC5 variant-positive group. Conclusions: ARMC5 pathogenic variants are common (71%) in Japanese patients with PMAH. p.R619∗ might be a hot spot in Japanese patients with PMAH. Asymptomatic or presymptomatic pathogenic variant carriers were found among the family members of the patients. Although 50% of ARMC5 variant carriers had nonadrenal neoplastic lesions, no LOH or second hit of ARMC5 in the tumor tissues was evident. The ARMC5 variant-positive mutant group showed a higher basal cortisol level than the negative group.
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