Trinucleotide repeat expansion and TCF4 gene expression in Fuchs endothelial corneal dystrophy

Abstract

Purpose : Fuchs endothelial corneal dystrophy (FECD) is an autosomal dominant disease with assorted variations in expression and penetrance. The expansion of a CTG trinucleotide repeat (TNR) in a different intron of transcription factor 4 (TCF4) has commonly been detected in FECD patients, and the sensitivity and specificity of >50 repeats was 79% and 96%, respectively (Wieben et al., PloS ONE, 2012). The purpose of this present study was to evaluate the TNR expansion in a larger cohort of Caucasian FECD patients.

Methods : We recruited 387 FECD patients (158 males and 229 females; mean age: 69.7±9.2 years; range: 32-92 years) who were scheduled to receive Descemet's membrane endothelial keratoplasty (DMEK) at the University of Erlangen-Nürnberg Hospital in order to obtain peripheral blood samples. All patients were diagnosed as FECD due to symptoms such as guttae, corneal edema, and decrease of corneal endothelial cell density. Purification of genomic DNA from each patient’s blood sample was carried out and the expansion of CTG repeats in the third intron of TCF4 was subsequently examined by polymerase chain reaction (PCR). The size of the products was determined by capillary electrophoresis. TNR was also confirmed by DNA sequencing of the PCR product.

Results : Genomic DNA from the blood of the FECD patient expressed 3 patterns: 1) CTG expansion of <50 repeats, 2) a heterozygous CTG expansion of >50 repeats, and 3) a homozygous CTG expansion of >50 repeats. Of the total 387 FECD patients, 226 (92 males and 134 females, 58.4%) did not possess a CTG expansion of >50 repeats, 134 (52 males and 82 females, 34.6%) harbored a heterozygous CTG expansion of >50 repeats, and 27 (14 males and 13 females, 7.0%) harbored a homozygous CTG expansion of >50 repeats. TNR expansion determined by the size of the PCR products was also confirmed by DNA sequencing.

Conclusions : The findings of this study involving a large cohort of Caucasian FECD patients provide additional evidence of the association between the intronic CTG expansion in TCF4 with FECD. How TNR causes disease, as well as the genetic background of patients without TNR expansion, are topics that require further investigation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.