Two Novel Mutations Found In Two Chinese Gelatinous Drop-like Corneal Dystrophy Families A Clinical, Histological And Genetic Study

Part OneObjective: To report clinical and histopathologic characteristics, postoperativeresults, and in vivo Confocal microscopic findings of gelatinous drop-like cornealdystrophy (GDLD) in two Chinese patients.Methods: Lamellar keratoplasty using cryopreserved donor cornea was carried outon the two patients diagnosed with GDLD and the corneal buttons were examined bylight and electron microscopy. The eyes were examined by in vivo Confocalmicroscopy before and after surgery.Results: Corneal buttons of both cases were manifested with subepithelialaccumulations of a Congo red positive substance, which showed fibrillar structurecharacteristics of amyloid fiber under electron microscopy. Bowman's layer wasdisrupted and replaced by the amorphous deposits. Scanning electron microscopy revealed that the corneal epithelial cells were less securely attached to each other than normal cells, with prominent gaps between adjacent cells. Transmission electron microscopy revealed that the basal epithelial cells contained numerous digitiform cell processes which were invaginated in the underlying amyloid deposits. The characteristic findings of Confocal microscopy were distorted and larger basal epithelial cells accompanied with abundant high reflective nodules located both between and under them. No obvious biomicroscopic and Confocal microscopic signs of recurrence were found during the follow up period in the two patients after surgery.Conclusion: The characteristic manifestation of GDLD is subepithelial accumulations of Congo red positive amyloid substance. Lamellar keratoplasty using cryopreserved donor tissue seemed effective for corneal transparency recovery for GDLD and may delay the recuurence. We describe the first in vivo Confocal microscopic study of GDLD. The advantages of in vivo Confocal microscopy for microstructural analysis of a living human cornea might provide useful information about the process of amyloid deposition and the recurrence after keratoplasty.Part TwoPurpose: To identify the genetic defect in TACSTD2 gene that cause gelatinous drop-like corneal dystrophy (GDLD) in two unrelated consanguineous Chinese families.Methods: Genomic DNA was prepared from leucocytes of peripheral venous blood.The coding region of the TACSTD2 gene was evaluated by means of polymerasechain reaction and direct sequencing.Results: Sequencing of the TACSTD2 gene of the two probands revealed two novelhomozygous frameshift mutations, c.84insG and c.480delC. The identified moleculardefect cosegregates with the disease among affected members of the families and isnot found in 50 unaffected controls.Conclusions: This study reports two novel mutations in two GDLD families andexpands the spectrum of mutations in TACSTD2 gene that may cause pathologicalamyloidosis in the corneas. This study improves the understanding of the geneticbasis of GDLD in China.