A novel phenotype-genotype correlation with an Arg555Trp mutation of TGFBI gene in Thiel-Behnke corneal dystrophy in a Chinese pedigree

Abstract

Background: To investigate the molecular defects in a four-generation Chinese pedigree affected with Thiel-Behnke corneal dystrophy (TBCD). And to further study the relationship between genetic mutation and clinical manifestations.

Methods: Individuals of the pedigree were recruited for extensive ophthalmic examinations. Histological studies of two corneal buttons obtained from lamellar keratoplasty were conducted. Peripheral blood was collected in EDTA for genomic DNA isolation from leukocytes of all affected and unaffected members. All 17 exons of the TGFBI gene were screened for mutations by polymerase chain reaction and direct DNA sequencing.

Results: Clinical examinations revealed a typical pattern of honeycomb-like TBCD. Histopathology study demonstrated eosinophilic deposits that were congo-red-positive and did not stain with periodic acid Schiff or Masson's trichrome. Genetic analysis disclosed a heterozygous p. Arg555Trp mutation resulted from a missense c. 1663C > T nucleotide change in exon 12 of TGFBI gene in all affected members. Morever, a second rare variant in exon 6 of the TGFBI gene (p. Arg257Trp) also cosegregated within this family and has been confirmed to be a single nucleotide polymorphism (SNP) not previously reported.

Conclusions: The p. Arg555Trp mutation of the TGFBI gene was associated with TBCD, which revealed a novel phenotype-genotype correlation within the mutational spectrum of phenotypically diverse corneal dystrophies.

Fig. 1

Pedigree of the four-generation Chinese family with autosomal dominant corneal dystrophy. Squares and circles indicate males and females, respectively. Black symbols indicate affected members and open symbols indicate unaffected individuals. The diagonal line indicates a deceased family member and the black arrow indicates the proband. Asterisks indicate family members who attend this study

Fig. 2

The affected family members’ corneal phenotype illustrating TBCD as shown by slit-lamp examination. Note the tiny superficial opacities of the proband’ daughter (IV:4), bilateral irregular corneal surfaces, multiple discrete, dense gray-white, honeycomb-shaped opacities in a geographic distribution of the proband (III:5), and extensive honeycomb-shaped configuration of grayish opacities beneath the epithelium and at the Bowman’s layer of the proband’s brother (III:1). Clear area appears around the corneoscleral limbus in all the patients. These images are published with the consent of the patients, and in the case of the 6-year old patient, with the consent of her parents

Fig. 3

Histopathologic examination of the excised corneal button from the proband. a Hematoxylin and eosin staining of the tissue section revealed an irregular, layered structure of the corneal epithelium with variable thickness in which eosinophilic deposits (asterisks) were noted predominantly beneath the epithelium and involved the anterior stroma within a small range (see the arrow). Note the obliterated Bowman’s layer and distorted epithelium with varied thickness. b Orange-coloured congo-red-positive deposits of amyloid aggregates with variable size and irregular shape are found in subepithelia area, extending into the entire stroma (arrowhead). c Numerrous small single Periodic acid Schiff (PAS) stain-negative deposits were noted throughout the corneal stroma, which disturbed the normal architecture of the stroma. d The deposits did not stain red with Masson’s trichrome. Note the apparent subepithelial fibrosis. e UBM scan demonstrated markedly increased reflectivity, due to deposits within the lesions and irregular epithelial thickening induced by corneal opacities which project into anterior stroma. f OCT-scan also confirmed an extensive sawtooth-like pattern of hyperreflective material deposited along the Bowman layer

Fig. 4

DNA sequence chromatograms of the proband. Note the heterozygous C > T nucleotide change in exon 12 and 6 of TGFBI gene (see the arrow) which altered the Arg to Trp and an unaffected individual (II:5) shows Arg at the same codon 555 and 257, respectively