Insights into keratoconus from a genetic perspective.

Keratoconus is a progressive and non-inflammatory thinning of the cornea, which may result in severe visual impairment due to irregular curvature and scarring. It can occur in isolation but is often seen in association with other systemic or ocular disorders. There is a well-recognised genetic component to keratoconus, as evidenced by family and twin studies; however, the aetiology of the disease is complex with both genetic and environmental factors playing a role. Over the last decade significant progress has been made in identifying genetic risk factors for keratoconus. Multiple approaches have been taken including candidate gene studies and genome-wide studies. VSX1 remains as the best characterised keratoconus gene but only accounts for rare cases. Other candidate genes with a role to play include SOD1, other corneal dystrophy genes such as ZEB1 and TGFBI and collagen genes. Family-based studies have recently led to the identification of the MIR184 gene for keratoconus with cataract and to the DOCK9 gene in a family with isolated keratoconus. Numerous other linkages have been reported and new sequencing technologies are set to rapidly expand the number of identified keratoconus genes in these regions. Similarly, recent genome-wide association studies in case-controlled cohorts have identified common variations in and around HGF, RAB3GAP1 and LOX as candidate risk factors for keratoconus. These gene identifications are beginning to reveal the molecular aetiology of keratoconus but despite this recent progress, there remain numerous genetic risk factors to be identified for this relatively common yet complex disease.