OBJECTIVE: ARMC5 is the most prevalent gene predisposing to primary bilateral macronodular adrenal hyperplasia (PBMAH), but germline KDM1A variants have been identified in the rare PBMAH associated with food-dependent Cushing's syndrome (FDCS). The purpose of this work was to assess the frequency of KDM1A variants in a large series of PBMAH patients. DESIGN: A total of 301 consecutive PBMAH index cases from 8 international endocrinology departments were included. Clinical, biological, and imaging data were collected retrospectively. RESULTS: Ten (3.3%) patients carried a germline KDM1A pathogenic or likely pathogenic variant, 60 (19.9%) carried a germline ARMC5 alteration, and 231 (76.8%) had no identified genetic predisposition. Food-dependent Cushing's syndrome was present in all patients with KDM1A variants and absent in the 2 other groups. KDM1A patients had a higher 24-h urinary free cortisol (3.0-fold upper limit of normal vs 1.36 for ARMC5 patients and 0.66 for wild-type patients, respectively, P = .0001). In accordance with FDCS pathophysiology, patients with KDM1A variants had a lower morning fasting plasma cortisol (192 nmol/L vs 407 and 428, respectively, P = .0003) and a higher midnight plasma cortisol (487 nmol/L vs 297 and 171.96, respectively, P = .0004). Morning/midnight plasma cortisol ratio below 0.65 holds 100% sensitivity and specificity for the detection of FDCS. All patients with KDM1A variants were women, vs 65% of ARMC5 patients and 67% of wild-type patients (P = .0337). CONCLUSIONS: KDM1A germline pathogenic variants are rare in PBMAH and account for <
5% of index cases. KDM1A seems constantly associated with FDCS, which can be evoked in front of a morning/midnight plasma cortisol ratio below 0.65.