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M. Mokhtarzadeh, M. L. Nickerson, S. Mahurkar, H. S. Kruth, J. Karkera, J. S. Weiss; Potential Indication for Genetic Testing in Difficult to Diagnose Schnyder's Corneal Dystrophy: Genotypic/Phenotypic Correlation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1014.
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Determine if there is a genotypic/phenotypic relationship in Schnyder’s crystalline corneal dystrophy (SCCD)
Patients with SCCD were recruited since 1987. IRB approved protocol included informed consent, ophthalmic examination, and DNA sequencing of the UBIAD1 gene. Slit lamp photographs of affected individuals were reviewed to determine if particular gene mutations were associated with specific phenotypes. Families with more than three individuals were used to make age matched phenotypic comparisons.
Slit lamp photos of 50 patients from 17 unrelated families were reviewed. Seven unique mutations have been identified in twelve of the families in this group. Genetic samples from the remaining five families are still being evaluated to identify a mutation. Twelve of the seventeen families (15 individuals) included only one or two affected members. Five families (35 individuals) included three or more affected members. Of the seven unique mutations, only the T175I mutation demonstrated a unique phenotype of prominent diffuse corneal haze with minimal or absent crystals. Because of the unusual phenotype, affected family members eluded diagnosis for decades despite consultation with multiple corneal subspecialists. All families demonstrated some predictable corneal changes on the basis of age. Two families with the same mutation (N102S), and three affected members each, had similar phenotypes in age matched affected individuals. One family with eleven affected individuals demonstrated a variety of distinct phenotypes, even among similarly aged individuals. There were three affected individuals with very similar phenotypes who each originated from different families with distinct gene mutations.
There is no clear genotype phenotype correlation in the majority of patients who we examined with SCCD. The T175I mutation appeared to have a unique phenotype. While genetic testing may not be relevant for the patient with a typical presentation of SCCD, it may be helpful in difficult to diagnose cases particularly if there is an atypical phenotype.
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