Background: Visual system homeobox gene (VSX1) plays a major role in the early development of craniofacial and ocular tissues including cone opsin gene in the human retina. To date, few disease-causing mutations of VSX1 have been linked to familial and sporadic keratoconus (KC) in humans. In this study, we describe the clinical features and screening for VSX1 gene in families with KC from India.
Methods: Clinical data and genomic DNA were collected from patients with clinically diagnosed KC and their family members. The study was conducted on 20 subjects of eight families from India. The coding exons of VSX1 gene were amplified using PCR and amplicons were analyzed by direct sequencing. Predictive effect of the mutations was performed using Polyphen-2, SIFT and mutation assessor algorithms. Additionally, haplotypes of VSX1 gene were constructed for affected and unaffected individuals using SNPs.
Results: In the coding region of VSX1, one novel missense heterozygous change (p.Leu268His) was identified in five KC patients from two unrelated families. Another family of three members had a novel heterozygous change (p.Ser251Thr). These variants co-segregated with the disease phenotype in all affected individuals but not in the unaffected family members and 105 normal controls. In silico analysis suggested that p.Leu268His could have a deleterious effect on the protein coded by VSX1, while p.Ser251Thr has a neutral effect on the functional properties of VSX1. Haplotype examination revealed common SNPs around the missense change (p.Leu268His) in two unrelated KC families.
Conclusions: In this study, we add p.Leu268His, a novel missense variation in the coding region of VSX1 to the existing repertoire of VSX1 coding variations observed in Indian patients with the characteristic phenotype of KC. The variant p.Ser251Thr might be a benign polymorphism, but further biophysical studies are necessary to evaluate its molecular mechanism. The shared haplotype by two families with the same variant suggests the possibility of a founder effect, which requires further elucidation. We suggest that p.Leu268His might be involved in the pathogenesis of KC, which may help in the genetic counselling of patients and their family.