Context: Primary Bilateral Macronodular Adrenal Hyperplasia (PBMAH) is a rare disease characterized by the presence of bilateral adrenal macronodules, that can cause hypercortisolism (Cushing syndrome). A first genetic cause of the non-syndromic presentation of PBMAH has been identified in 2013: germline inactivating heterozygous mutations of the tumor suppressor gene ARMC5, involved in 20 to 25% of cases. The bilateral adrenal involvement and the description of familial cases without ARMC5 mutation suggest different genetic predisposition factors. PBMAH is a clinically, biologically and radiologically heterogeneous disease with various presentations, from bilateral adrenal incidentalomas without specific clinical sign of Cushing syndrome to massively enlarged adrenals associated with severe hypercortisolism.

Objectives: To understand the clinical heterogeneity of PBMAH, identify new causing genes, and improve clinical, biological and radiological characterization of PBMAH patients.

Methods: The clinical data of 352 index case patients with ARMC5 genotyping have been collected to study the genotype/phenotype correlation. All ARMC5 mutations have been listed, both those already published and those identified in our center. A multi-omics analysis – with RNAseq, methylome, miRNome, exome sequencing and SNP array – has been performed in the adrenal tissues from 36 patients with PBMAH treated by adrenalectomy.

Results: The analysis of the 352 genotyped index case patients confirms that ARMC5 mutated patients have a more severe phenotype than wild-type patients, regarding the intensity of the Cushing syndrome and the adrenal involvement. All mutated patients had a clear bilateral adrenal involvement on imaging and at least a possible mild autonomous cortisol secretion, defined by a plasma cortisol after low dose dexamethasone overnight suppression above 50 nmol/L, while these criteria were inconstant in the non-mutated patients. The association of these two criteria holds a 100% sensitivity for the detection of an ARMC5 mutation. We propose that ARMC5 genotyping should be conditional to the presence of these two simple criteria in order to increase the yield of genetic screening, with a mutation rate near 20%. We present a list of 133 different germline variants of ARMC5, including 38 never reported in the literature. Most of these alterations are non-sense, missense and frameshift variants. The evaluation of the pathogenic nature of some missense variants may be difficult, and rests on a beam of arguments taking into account the frequency of the variants in the general population, their segregation in familial cases, in silico predictions, the identification of second somatic hits, and the functional studies when available. Our analysis and functional data allow a better classification for numerous missense variants. The integrative analysis of the genomic data of the samples from the 36 PBMAH patients identifies three distinct molecular groups: G1, comprising the tumors from the ARMC5 mutated patients; G2, which comprises the tumors from the patients with food-dependent Cushing syndrome, mediated by the illegitimate expression of the GIP receptor in adrenocortical cells; and G3, with the tumors from the remaining patients presenting a more heterogeneous phenotype. The analysis of exome data identifies germline inactivating heterozygous mutations of KDM1A in 5/6 G2 patients, constantly associated with a somatic loss of heterozygosity of the short arm of chromosome 1 (1p) harboring the KDM1A locus, thus leading to a biallelic inactivation of the gene.

Conclusion: These studies allow a better characterization of PBMAH patients, through the demonstration of distinct molecular groups correlated with the clinical heterogeneity of the disease, the identification of predictive criteria for ARMC5 mutation, and the discovery of the genetic cause of PBMAH associated with food-dependent Cushing syndrome: the tumor suppressor gene KDM1A.

Keywords:

Primary Bilateral Macronodular Adrenal Hyperplasia, PBMAH, Cushing, cortisol, food-dependent Cushing syndrome, glucose-dependent insulinotropic peptide, GIP, GIPR, genetics, genomics, ARMC5, KDM1A