TCF4 Triplet Repeat Expansion and Nuclear RNA Foci in Fuchs' Endothelial Corneal Dystrophy.
PURPOSE
Expansion of the intronic CTG18.1 triplet repeat locus within TCF4 contributes significant risk to the development of Fuchs' endothelial corneal dystrophy (FECD) in Eurasian populations, but the mechanisms by which the expanded repeats result in degeneration of the endothelium have been hitherto unknown. The purpose of this study was to examine FECD endothelial samples for the presence of RNA nuclear foci, the hallmark of toxic RNA, as well as evidence of haploinsufficiency of TCF4.


METHODS
Using fluorescence in situ hybridization, we examined for the presence of nuclear RNA foci containing expanded CUG transcripts in corneal endothelial samples from FECD subjects with CTG18.1 expansion. We also examined for any changes in expression levels of TCF4 by quantitative real-time PCR.


RESULTS
Numerous discrete nuclear RNA foci were identified in endothelial samples of FECD subjects (n = 8) harboring the CTG18.1 expansion, but not in controls lacking the expansion (n = 5) (P = 7.8 × 10(-4)). Percentage of cells with foci in expansion-positive endothelial samples ranged from 33% to 88%. RNA foci were absent in endothelial samples from an FECD subject without CTG18.1 expansion and a subject with endothelial dysfunction without FECD. Expression of the constitutive TCF4 exon encoding the basic helix-loop-helix domain was unaltered with CTG18.1 expansion.


CONCLUSIONS
Our findings suggest that the RNA nuclear foci are pathognomonic for CTG18.1 expansion-mediated endothelial disease. The RNA nuclear foci have been previously found only in rare neurodegenerative disorders caused by repeat expansions. Our detection of abundant ribonuclear foci in FECD implicates a role for toxic RNA in this common disease.
['Mootha|V Vinod|VV|', 'Hussain|Imran|I|', 'Cunnusamy|Khrishen|K|', 'Graham|Eric|E|', 'Gong|Xin|X|', 'Neelam|Sudha|S|', 'Xing|Chao|C|', 'Kittler|Ralf|R|', 'Petroll|W Matthew|WM|']
D000368:Aged D000369:Aged, 80 and over D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors D004728:Endothelium, Corneal D005260:Female D005642:Fuchs' Endothelial Dystrophy D020022:Genetic Predisposition to Disease D005838:Genotype D006801:Humans D017404:In Situ Hybridization, Fluorescence D008297:Male D008875:Middle Aged D015138:RNA, Nuclear D000073940:Transcription Factor 4 D014157:Transcription Factors D019680:Trinucleotide Repeat Expansion
TCF4 triplet repeat expansion Fuchs' endothelial corneal dystrophy CTG18.1 RNA nuclear foci