USP8 Mutations in Pituitary Cushing Adenomas-Targeted Analysis by Next-Generation Sequencing

Area of Science:

• Endocrinology
• Molecular Genetics
• Oncology

Background:

• Gain-of-function somatic mutations in the ubiquitin specific protease 8 (USP8) gene are implicated in pituitary adenomas causing Cushing disease.
• Molecular diagnostics can assist in analyzing tumor tissue from transsphenoidal surgery, but small tumor size and normal tissue contamination pose challenges.

Purpose of the Study:

• To evaluate the utility of molecular testing for USP8 mutations in formalin-fixed and paraffin-embedded (FFPE) pituitary adenoma tissues from Cushing disease patients.
• To compare the sensitivity of Sanger sequencing and targeted next-generation sequencing (NGS) for USP8 mutation detection.

Main Methods:

• DNA was isolated from single FFPE tissue sections of 42 pituitary adenomas.
• Sanger sequencing and targeted NGS were employed to identify USP8 missense mutations.
• Mutation frequencies were analyzed in relation to patient demographics and tumor characteristics.

Main Results:

• USP8 mutations were identified in 9 out of 42 tumors (21.4% frequency).
• NGS detected mutations in three additional tumors missed by Sanger sequencing, with mutant allele frequencies as low as 3%.
• Mutations were more frequent in female patients (25.9%) than male patients (13.3%).

Conclusions:

• Testing for USP8 variants is feasible using small amounts of FFPE tissue.
• NGS offers higher sensitivity for detecting USP8 mutations compared to Sanger sequencing.
• Assessment of USP8 mutations can complement histopathological diagnosis of pituitary adenomas in Cushing disease.