Distinguishing benign from pathogenic duplications involving GPR101 and VGLL1-adjacent enhancers in the clinical setting with the bioinformatic tool POSTRE.

Structural variants (SVs) that disrupt topologically associating domains can cause disease by rewiring enhancer-promoter interactions. Duplications involving GPR101 are known to cause X-linked acrogigantism (X-LAG) through ectopic GPR101 expression, but not all of these duplications are pathogenic. This presents a diagnostic challenge, especially in the prenatal setting. We evaluated POSTRE, a tool that predicts the regulatory impact of SVs, to distinguish pathogenic from benign GPR101 duplications. We analyzed seven non-pathogenic duplications and 27 known X-LAG-associated duplications. To enable predictions in an X-LAG-relevant tissue, enhancer maps built using H3K27ac ChIP-seq, ATAC-seq, and RNA-seq data derived from human anterior pituitary samples (NIH research protocol 97-CH-0076, Clinicaltrials.gov Identifier NCT00001595, submitted on 11 March 1999) were integrated into POSTRE. POSTRE correctly classified all 34 duplications as benign or pathogenic. In addition, one X-LAG case with mild clinical features (i.e. severe growth hormone hypersecretion without pituitary tumorigenesis) was found to include only 2/5 VGLL1 enhancers, whereas all typical X-LAG cases had ≥4 enhancers duplicated. This suggests that partial enhancer hijacking at VGLL1 could explain the different clinical features in this individual. These findings support the utility of POSTRE to support diagnostic pipelines when interpreting SVs affecting chromatin architecture in pituitary disease and highlight its potential to reduce uncertainty in genetic counseling without requiring chromatin conformation capture assays.