CushieBlog

Summary: In Cushing’s disease (CD), pituitary corticotroph adenomas secrete excessive adrenocorticotropic hormone (ACTH), resulting in hypercortisolism. Often, the genetic pathogenesis of CD remains unknown, but recent studies have shown that the ubiquitin-specific protease 8 gene (USP8) is frequently mutated in CD. This gene codes for a protein deubiquitinase that inhibits the lysosomal degradation of the epidermal growth factor receptor. Researchers determined that pediatric patients with USP8 mutations were predominantly female and presented with higher ACTH levels than control patients.

Methods:

• To further study the prevalence of mutations in USP8, researchers sequenced the complete USP8-coding and surrounding intronic regions in 97 patients with diagnosed CD by Sanger sequencing of germline DNA (n=97) and tumor DNA (n=50).
• They analuzed biochemical and clinical characteristics in all the patients with predicted (by in silico analysis) damaging USP8 mutations and it was compared to patients without the mutation (control).

Results:

• Overall researchers identified 18 (18.5%) patients with corticotroph adenomas who had USP8mutations, 13 with germline mutation, 2 with a germline and a new somatic mutation, and 5 with somatic mutation only.
• All the somatic mutations that were not present at the germline level were mutations in the previously described hotspot.
• Female-to-male ratio in the patients with USP8 mutations was 3.5:1 compared to the control ratio of 1:1 (P=0.05).
• The mean age was 13 years old (range 6-18) and 72% (13/18) were whites.
• Three of the mutant tumors were macroadenomas (≥ 1 cm) and 15 were microadenomas (< 1 cm).
• In cases, mean basal plasma ACTH was 53.2±28.5 pg/mL and 39.6±19.1 pg/mL in the control group (P=0.02).
• Researchers did not note any statistically significant differences in cortisol levels between the groups.