Mutations in the keratin gene as a cause of Meesman-Wilke corneal dystrophy and autosomal dominant skin cornification disorders

Abstract

Meesmann's corneal dystrophy (OMIM 122,100) is a rare autosomal dominant disorder of the corneal epithelium. It manifests in early childhood and affects both eyes. The disease is characterized by variable patterned dot-like corneal opacities and intraepithelial vesicles, which can be seen by slit-lamp examination and retro-illumination. Further signs include punctate erosions, lacrimation, photophobia, and blepharospasm. Vision is usually only slightly diminished. By histology, the corneal epithelium is irregularly thickened. It shows vacuolated epithelial cells and intraepithelial formation of vesicles. By electron microscopy fibrogranular aggregates are seen in the cytoplasm of epithelial cells. Linkage analyses in descendants of the family described by Meesmann and Wilke and other affected kinships showed that the putative genetic defect locates within the keratin type I gene cluster on chromosome 17 (17q12-21). Molecular genetic analyses in more than ten affected families showed that mutations in the cornea-specific keratin genes K3 and K12 represent the causative genetic defects of the disease phenotype. Comparative studies in autosomal dominant skin disorders of cornification suggest that the mutations identified in patients with Meesmann's corneal dystrophy exert dominant negative effects on keratin filament assembly. Disturbed filament formation results in intracellular keratin clumping, identifiable as fibrogranular aggregates. As a result the mechanical resilience of the affected cells and the epithelial tissue appears markedly reduced. Whether abnormalities of functionally related structural proteins, e.g. desmosomal components, could result in a phenotype similar to Meesmann and Wilke's corneal dystrophy remains to be seen.