Somatic hotspot variants rarely coexist with germline drivers of Cushing’s disease

LC. Hernández-Ramírez*^a (Dr), FR. Faucz^b (Dr), N. Pankratz^c (Dr), J. Lane^c (Dr), P. Chittiboina^d (Dr), DM. Kay^e (Dr), JL. Mills^f (Dr), CA. Stratakis^g (Dr)

^a Red de Apoyo a la Investigación, Coordinación de la Investigación Científica, Universidad Nacional Autónoma de México e Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Cdmx, MEXICO ; ^b Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Md, UNITED STATES ; ^c Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis, Mn, UNITED STATES ; ^d Neurosurgery Unit for Pituitary and Inheritable Diseases, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Md, UNITED STATES ; ^e Newborn Screening Program, Wadsworth Center, New York State Department of Health, Albany, Ny, UNITED STATES ; ^f Division of Intramural Population Health Research, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Md, UNITED STATES ; ^g Human Genetics & Precision Medicine, IMBB, FORTH, Heraklion, Crete and ELPEN Research Institute, Athens, GREECE

* lauracristinahdz@gmail.com

Introduction. Recurrent somatic hotspot variants have been found in a plurality of adult and a minority of pediatric corticotropinomas. In contrast, causative germline defects are not rare in children with Cushing’s disease (CD) but are very infrequent in adults. The overlap and interactions between germline and somatic variants in patients with CD are unknown. We sought to determine the frequency of CD-associated somatic hotspot variants in a large pediatric-enriched cohort of patients with CD, and to analyze the overlap of somatic and germline variants.

Methods. The cohort comprised 120 individuals (55.8% females, 92.5% pediatric). Paired germline and corticotropinoma whole exome sequencing (WES) was performed in 27 cases. For 93 patients (78 with germline WES and one with gene-specific analysis), targeted Sanger-based screening of BRAF (n=1), USP8 (n=19), BRAF/USP8 (n=6), USP8/USP48 (n=3), or BRAF/USP8/USP48 (n=64) somatic hotspots was performed.

Results. Eighteen patients (15.1%, including two adults) carried somatic USP8 variants, and one pediatric patient carried the USP48 p.M415V variant (1.1%); none had the BRAF p.V600E variant. Potentially pathogenic germline defects were identified in 21 patients (19.8%), including one adult. One patient carried three germline variants of uncertain significance (VUS) in CD-associated genes and two individuals displayed somatic loss of the normal allele; the rest had no apparent second hits. One child had both somatic hotspot and germline variants (USP8 p.720R and CDKN1B p.I119T). Since CDKN1B p.I119T was classified as VUS, it was unclear if both variants or only USP8 p.720R acted as drivers. Excluding that case, pediatric patients with somatic USP8 variants were older at disease onset than those carrying germline variants (12.6±2.1 vs. 10.2±2.8 years, P=0.047), and older than those negative for both somatic and germline variants (10.1±3.2 years, P=0.008).

Discussion. In our cohort of patients with CD, the overlap between potentially pathogenic germline and somatic hotspot variants was very infrequent (0.05%). Pediatric patients carrying USP8 hotspot variants are characterized by an older age at disease onset. Our results indicate that somatic hotspot variants and germline defects are two groups of genetic drivers that independently lead to CD.

The author has declared no conflict of interest.