Screening for Novel LOX and SOD1 Variants in Keratoconus Patients from Brazil.

Diego Nery Benevides Gadelha,Dáfine De Oliveira Andrade,Nathalia Mayanna Da Paz Silva,Luana Talita Antunes,Sebastião Cronemberger,Bruno Luiz Fonseca Schamber-Reis,Matheus Alencar De Oliveira,Alex Felipe Barbosa Feitosa,Matheus Cavalcanti Muniz,Rafaela Gomes Da Silva

doi:10.18502/jovr.v15i2.6730

Diego Nery Benevides Gadelha, Dáfine De Oliveira Andrade + Show 8 more

Open Access

https://doi.org/10.18502/jovr.v15i2.6730

Copy DOI

Abstract

PurposeTo investigate the presence of the variants of lysyl oxygenase (LOX) and superoxide dismutase 1 (SOD1) genes in Brazilian patients with advanced keratoconus.Methods Donor genomic DNA extracted from blood samples was screened for 5'UTR, exonic LOX, and SOD1 variants in a subset of 26 patients presenting with advanced keratoconus (KISA 1000% and I–S 2.0) by Sanger sequencing. The impact of non-synonymous amino acid changes was evaluated by SIFT, PMUT, and PolyPhen algorithms. The Mutation Taster tool was used to evaluate the potential impact of formation of new donor and acceptor splice sites in the promoter region of affected volunteers carrying sequence variants. A 7-base SOD1 deletion (IVS2 + 50del7bp) previously associated with keratoconus was screened in 140 patients presenting classical keratoconus by gel fragment analysis, and positive samples were sequenced for confirmation.ResultsWe found an unreported missense variant in LOX exon 6 in one heterozygous patient, leading to substitution of proline with threonine at residue 392 (p. Thr392Pro) of LOX protein sequence. This mutation was predicted to be potentially damaging to LOX protein. Another LOX variant, Arg158Gln, was also detected in another patient but predicted to be non-pathogenic. Two additional new polymorphisms in LOX 5'UTR region (–116C T and –58C T) were found in two patients presenting with advanced keratoconus and were predicted to modulate or create donor/acceptor splice sites in LOX transcripts. Additionally, SOD1 deletion was detected in one patient presenting with severe keratoconus, not in control samples.ConclusionWe described three novel LOX polymorphisms identified for the first time in Brazilian patients with advanced keratoconus, as well as a previously described SOD1 deletion strongly associated with keratoconus. A possible role of these variants in modulating transcript levels in the cornea of affected individual requires further investigation.

Highlights

Keratoplasty is the most frequent tissue transplantation in Brazil, comprising 60% of all organ and tissue transplantations in the country.[1]
The implication of superoxide dismutase 1 (SOD1) and lysyl oxygenase (LOX) mutations on KC development may be important risk factors for the disease and their involvement in disease pathogenesis depends on additional studies on different ethnicities.[25, 33]. Considering that this pathology is considered a major public health issue in Brazil, the aim of this study was to investigate the presence of genetic variants in SOD1 and LOX genes in individuals affected by advanced KC
We found two nonsynonymous mutations in LOX, namely Arg158Gln and Thr392Pro, and an intronic SOD1 deletion previously associated with KC development

Summary

Introduction

Keratoplasty is the most frequent tissue transplantation in Brazil, comprising 60% of all organ and tissue transplantations in the country.[1]. Clinical signs of KC usually manifest first at puberty and in young adults leading to visual deterioration due to irregular astigmatism, myopia, and corneal scarring in about 20% of patients.[2, 3] KC manifests in only one eye in most patients, the disease can progress to bilaterality in severely affected individuals.[4] Histologically, KC is characterized by impaired collagen secretion resulting from degeneration of keratocytes as well as by epithelial and stromal changes leading to disorganization of fibers involved in tissue resistance and stability.[5] KC incidence is estimated at 1/2,000 individuals in the general population, with a prevalence of 50 to 230 cases/100,000 in Western countries.[6] Diagnosis is usually based on qualitative corneal topography and quantitative videokeratography of posterior corneal surface confirmed by a KISA index > 100%.[7] Refractive error in KC can be corrected with glasses or contact lenses. About 20% of patients have more advanced disease, for which Ferrara intrastromal corneal ring segments (Ferrara rings) are recommended, along with penetrating keratoplasty in most cases.[6, 8]

Objectives

Methods

Results

Conclusion