Macular corneal dystrophy related to novel mutations of CHST6 in a Chinese family and clinical observation after penetrating keratoplasty

Background Macular corneal dystrophy (MCD) is a rare corneal stromal dystrophy with bilateral progressive vision loss. The pathogenic gene of MCD is carbohydrate sulfotransferase 6 (CHST6). Herein, we report a novel missense mutation and a rare exon deletion mutation in the CHST6 gene in a Chinese family with MCD. Methods Genomic DNA was extracted from the peripheral blood, and next generation sequencing was used to analyse the gene sequence. The pathogenic mutations were identified in all affected family members. The proband successively received binocular penetrating keratoplasty (PKP), and the corneas were examined by histopathology and colloidal iron staining to prove the diagnosis. A long-term follow-up was made to observe the changes after PKP. Results Genetic analysis demonstrated hemizygous mutations in the proband, including a novel c.520A>C (p.K174Q) missense mutation and a rarely reported exon 3 deletion mutation, which were co-segregated with the MCD phenotypes in the pedigree. The positive colloidal iron staining confirmed the diagnosis of MCD in the proband. However, the clinical phenotype and pathological manifestation of both eyes were different from each other because of complicated keratitis in the left eye. During the nine years of follow-up, visual acuity was improved significantly, and the cornea was transparent without rejection and postoperative recurrence in both eyes. Conclusions The novel hemizygous mutations were thought to contribute to the loss of CHST6 function, which induced typical clinical and pathological features of MCD. PKP was an effective treatment for MCD.

Detailed corneal and genetic characteristics of a pediatric patient with macular corneal dystrophy - case report

Background Corneal dystrophies are a group of rare, inherited disorders that are usually bilateral, symmetric, slowly progressive, and not related to environmental or systemic factors. The majority of publications present the advanced form of the disease with a typical clinical demonstration. The initial signs and symptoms of different epithelial and stromal corneal dystrophies are not specific; therefore, it is very important to establish the early characteristic corneal features of these disorders that could guide the diagnostic process. Case presentation The main purpose of this study was to report the differential diagnosis of a pediatric patient with bilateral anterior corneal involvement suspected of corneal dystrophy. An 8-year-old male patient presented with asymptomatic, persistent, superficial, bilateral, diffuse, anterior corneal opacities. Slit lamp examination results were not specific. Despite the lack of visible stromal involvement on the slit lamp examination, corneal analysis based on confocal microscopy and optical coherence tomography revealed characteristic features of macular corneal dystrophy (MCD). The diagnosis of MCD was confirmed by CHST6 gene sequencing. The early corneal characteristic features of MCD, established based on the findings of this case report, include corneal astigmatism (not specific), diffuse corneal thinning without a pattern of corneal ectasia (specific), and characteristic features on confocal microscopy (specific), including multiple, dark, oriented striae at different corneal depths. Conclusions The clinical examination should be complemented with corneal imaging techniques, such as confocal microscopy and optical coherence tomography. In patients suspected of corneal dystrophy, genetic testing plays an important role in establishing the final diagnosis.

CHST6-related macular corneal dystrophy: a matter of endothelium

Macular corneal dystrophy (MCD) is classified as corneal stromal dystrophy. In this study, we retrospectively reviewed the surgical outcomes of 118 MCD patients receiving surgical treatment in the past 30 years and found patients receiving penetrating keratoplasty had the lowest recurrence rate 13.75%, compared with 40.91% patients receiving deep anterior lamellar keratoplasty and 25% receiving phototherapeutic keratectomy. Transcriptomic analysis in human corneal single-cell sequencing atlas found the MCD pathogenic gene CHST6 was abundant in corneal endothelium rather than other cell types. CHST6 protein showed a similar expression pattern to its mRNA. The mouse homologous gene Chst5 was 120-fold higher in corneal endothelium than in the epithelial and stromal layers. Mice with specifically Chst5 knockdown in the endothelial layer by microinjection of the adeno-associated virus serotype 9 - shRNA plasmids into the anterior chamber, rather than Chst5 knockdown into the stroma, showed MCD-like phenotypes. Corneal opacification and abnormally larger collagen fibrils were observed in the endothelial Chst5 knockdown mice. The same corneal characteristics were observed after overexpressing human CHST6 mutant R50H in the mouse endothelium. These observations indicating the pathogenesis of MCD is more related to the corneal endothelium rather than the stroma.