ISSN: 2155-9570
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Case Report - (2013) Volume 4, Issue 5
Purpose: This study aims to observe the ocular phenotypes of a family with Schnyder corneal dystrophy (SCD) and to assess the image features of SCD by in vivo laser corneal confocal microscopy (IVCM).
Methods: A family with SCD was collected, and the corneal lesion of five affected members was observed. Bilateral corneas were examined using IVCM (Heidelberg Retina Tomograph III with Cornea Module) in three adult patients with SCD. Blood samples were collected for genetic analysis in the available family members.
Results: Phenotype heterogeneity was found in five affected individuals with a same mutation (N102S). Slit-lamp examination suggested no crystal in the right eye of a 40-year-old male SCD patient, but crystalline materials were found by IVCM. In some images of IVCM, crack-like striaes and crystalline materials with various shapes were observed in the stroma.
Conclusions: Extremely varied phenotypes between individual patients are demonstrated in this SCD family with a same mutation locus. Slit-lamp examination cannot find mini crystalline deposits in SCD cornea. Crystalline accumulations can be detected by ICVM at the cellular level prior to slit-lamp examination.
Keywords: Schnyder corneal dystrophy, Corneal dystrophy, In vivo laser confocal microscopy, Confocal microscopy, UBIAD1 gene
Schnyder corneal dystrophy (SCD) is a rare, autosomal dominant inherited corneal disorder with high penetrance that affects the central and peripheral cornea and is characterized by cholesterol and phospholipid deposition. Those depositions are mainly localized in the corneal epithelium and stroma, and in some cases, the endothelium is involved leading to progressive corneal opacity [1,2]. Corneal crystals which are present only in 54% of SCD patients can facilitate the disease diagnosis [3]. This report documented a Chinese SCD family and further clarified its ocular phenotypes. In this study, we also clarified image features of SCD by IVCM.
After informed consent, five affected individuals from a Chinese SCD family were examined and their clinical features were recorded. Three adults among them also received IVCM examination. SCD diagnosis was based on clinical manifestations and genotype analysis of UBIAD1 gene.
In vivo corneal confocal microscopy examination
IVCM [Heidelberg Retina Tomograph III with Cornea Module (HRT III/CM)] was performed on three affected individuals with SCD. Longitudinal resolution of HRT III/CM is 1 μm. A 670 nm diode laser as the light source was applied in HRT III/CM. Before the examination, one drop of topical anesthesia of 0.5% proparacaine hydrochloride (Alcaine, Alcon) was instilled in both eyes. After applying a large drop of contact gel (Berlin, Germany Subsidiary of Bausch and Lomb) on the front surface of the microscope lens. Then, the cornea was accurately examined layer by layer using IVCM.
Genetic analysis
After obtaining informed consent, blood samples were collected (5 ml of blood in EDTA) from the available family members for a molecular genetic analysis. We extracted genomic DNA from peripheral blood leukocytes according to standard procedures. Exons 1 and 2 of UBIAD1 were amplified by polymerase chain reaction (PCR) using a 25 μl reaction mixture, containing 10× PCR buffer solution (2.5 μl), 2.5 mM dNTPs mixture (2 μl), 50 mM MgCl2 (0.75 μl), forward (5 μM) and reverse (5 μM) primers (1 μl each), Platinum® Taq polymerase (0.2 μl) obtained from Invitrogen Biotechnology Co. Ltd (Shanghai, China), sterile distilled water (16.55 μl) and DNA template (1 μl). Primers for the two coding exons of UBIAD1: 1F-CTC GTG GGG TGT AAG ACC CAC TT, 1R-GCG GCT TAA ATT AGA AAG CCA CCT; 2F-AGT GCC CAC CTG CAC AGT CTA AG, 2R-CAA ACT GGG CAG CTC CTT TAC AA. The target DNA regions were amplified with the following PCR settings: initial 5 min denaturation step at 94°C and a final 5 min extension step at 72°C with an intervening 30 cycles of 30 s denaturation at 94°C, 30 s annealing at 55°C and 30 s extension at 72°C; the samples were maintained at 4°C until use (PCR Amplifier using ABi9700). Amplicons were evaluated using agarose gels and then sequenced on a 3730XL DNA Analyzer.