Tissue-specific TCF4 triplet repeat instability revealed by optical genome mapping

Area of Science:

• Genomics
• Ophthalmology
• Molecular Biology

Background:

• Fuchs endothelial corneal dystrophy (FECD) is a common human repeat-mediated disease.
• It affects corneal endothelial cells (CECs) and is often linked to TCF4 intronic triplet repeats (CTG18.1).
• Understanding the tissue-specific instability of these repeats is crucial for FECD pathophysiology.

Purpose of the Study:

• To investigate the tissue-specific instability of the CTG18.1 repeat in FECD using optical genome mapping (OGM).
• To gain mechanistic insights into how CTG18.1 instability contributes to FECD.
• To explore the potential of OGM as a tool for analyzing repeat instability in disease.

Main Methods:

• Applied OGM to genomic DNA from FECD patients and controls (n=43), including CECs, leukocytes, and fibroblasts.
• Developed a bioinformatics pipeline to analyze CTG18.1-spanning DNA molecules.
• Compared OGM results with conventional polymerase chain reaction-based fragment analysis.

Main Results:

• Expanded CTG18.1 alleles showed dynamic behavior across different cell types.
• Clusters of CTG18.1 molecules (approx. 1800-11,900 repeats) were exclusively found in diseased CECs from expansion-positive FECD cases.
• Progenitor allele size and patient age influenced leukocyte-specific CTG18.1 instability.

Conclusions:

• OGM is a powerful tool for analyzing somatic instability of repeat loci.
• Extreme CTG18.1 instability in diseased CECs is a key factor in FECD pathophysiology.
• These findings suggest new therapeutic avenues for FECD and other diseases caused by somatically unstable repeats.