Integrated clinical–genetic–pathological analysis expands the phenotypic and molecular spectrum of PPNAD across carney complex and isolated forms

CONTEXT: Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of ACTH-independent Cushing syndrome (CS), occurring in isolation or as part of Carney complex (CNC); its phenotypic and molecular spectra remain incompletely defined. OBJECTIVE: To characterize phenotypic variability, genotype-phenotype correlations, and molecular findings in PPNAD through integrated clinical, histopathological, and genetic analyses. METHODS: We evaluated 18 index patients with PPNAD (15 with CNC, 3 isolated) and performed cascade genetic screening in relatives (20 variants-positive). Clinical, hormonal, imaging and histopathological data were reviewed; germline and somatic analyses employed targeted next-generation sequencing and copy-number assessment. RESULTS: Overt CS was present in 83% of index cases; 17% had cyclic hypercortisolism. Pathogenic or likely-pathogenic germline PRKAR1A variants were identified in 70.6% probands, including four novel variants; germline PRKACA duplications were detected in two cases. Cascade screening identified eight asymptomatic variant-positive relatives, in whom mild autonomous cortisol secretion (MACS) was observed. Somatic second-hit alterations in tumor tissue included PRKACA duplication, a PRKAR1A frameshift deletion, and 17q24.2 loss of heterozygosity. Histology most often showed classic PPNAD but also nonclassical patterns, expanding the morphological spectrum. Extra-adrenal manifestations were frequent (lentigines 61%, cardiac myxomas 22%). CONCLUSION: In this referral cohort, PPNAD/CNC displays marked phenotypic variability, incomplete penetrance with subclinical cortisol excess, and diverse molecular mechanisms, including novel germline variants and somatic second hits. Some cases lacked identifiable drivers, suggesting additional uncharacterized mechanisms. Systematic genetic screening and recognition of MACS are important for early diagnosis and long-term management.