Meesmann Corneal Dystrophy with Epithelial Basement Membrane Abnormalities: Clinical and Genetic Analysis of Two Families with Novel and Known Mutations in KRT3 and KRT12

This study describes the clinical and genetic features of Meesmann epithelial corneal dystrophy (MECD) in two unrelated families and reports new genotype-phenotype associations. Ten patients from a Lebanese family (<i>n</i> = 4) (Family 1) and a Spanish family (<i>n</i> = 6) (Family 2) underwent ophthalmologic evaluation, in vivo confocal microscopy (IVCM), anterior segment optical coherence tomography (AS-OCT) with epithelial thickness mapping (ET-map), and targeted next-generation sequencing (NGS) using a custom-designed 133-gene panel associated with anterior segment dystrophies. In Family 1, a novel homozygous <i>KRT12</i> c.1181T>C (p.Leu394Pro) variant was identified in the symptomatic proband and his clinically asymptomatic brother, while both parents, who were first cousins, were heterozygous for this nucleotide variant. The proband also carried the heterozygous <i>KRT3</i> c.250C>T (p.Arg84Trp) variant, which has been previously reported but, to our knowledge, has not been described in co-occurrence until now. In addition, the proband showed a complex phenotype with signs of MECD and epithelial basal membrane alterations consistent with epithelial basement membrane dystrophy (EBMD). In Family 2, four affected members carried the <i>KRT3</i> c.1492G>A (p.Glu498Lys) variant in heterozygosity, which has been previously described. The elderly members affected showed typical signs of MECD and EBMD. To our knowledge, these concomitant alterations have not been previously described with genetical confirmation. In conclusion, this study provides the first evidence that the co-occurrence of variants in two Meesmann corneal dystrophy-associated genes <i>(KRT3</i> and <i>KRT12</i>) can jointly account for the disease phenotype. We also highlight the association of MECD with EBMD in both families. Characterization using IVCM and AS-OCT ET-Map provides a deeper understanding of the morphological changes and phenotypic variability in MECD, confirming the utility of this multimodal imaging approach for diagnosis and management.