Background: Testicular Adrenal Rest Tumors (TARTs) are a common complication in patients with Congenital Adrenal Hyperplasia (CAH) leading to irreversible damage of the testes and infertility. The origin and etiological features of these benign tumors are unclear. It was hypothesized that TART is derived in utero from adrenal rests that fail to regress due to the elevated adrenocorticotropin hormone levels in CAH patients. However, next to adrenal characteristics, also testicular characteristics have been reported for TART, suggesting a more pluripotent progenitor as the origin of TART.

Objective: This study aims to unravel the origin and etiological features of TART.

Methods: RNA sequencing data of 14 TART, 11 adult adrenal-, 10 adult testis-, 13 fetal adrenal -and 5 fetal testis-tissues was obtained. The origin of TART is explored using unsupervised hierarchical clustering analysis and principle component analysis. TART-specific functional characteristics and pathways were identified using differential expression analysis (DESeq2), followed by Gene Ontology (GO) enrichment analysis and KEGG pathway analysis.

Results: Clustering analysis indicated highest similarity of TART with adult adrenal tissue and least similarity with fetal adrenal and fetal testis tissue. Differential expression analysis identified 747 genes differentially expressed in TART compared to adult adrenal tissue and 1901 genes differentially expressed in TART compared to adult testis tissue (fold-change > 2; adjusted p-value < 0.05). Functional annotation and pathway analysis of the 503 upregulated genes in TART compared to adult testis tissue revealed enriched GO-terms and pathways associated with steroid metabolism and receptor binding. Analysis of 463 upregulated genes in TART versus adult adrenal tissue highlighted GO-terms and pathways involved in extracellular matrix organization/remodeling.

Conclusion: This study corroborates the similarity of TART with adult adrenal tissue. GO enrichment analysis and pathway analysis confirm the adrenal steroidogenic and fibrotic properties of TART.