TCF4 and Fuchs endothelial corneal dystrophy: Expansion of a trinucleotide repeat, CTG18.1, in intron 2 of the TCF4 gene, is strongly associated with FECD in Europeans, so much so that it appears to be in effect a near-Mendelian allele which is the main cause of the condition in this population, accounting for between 73 and 79% of cases [2–4].