A recurrent de novo mutation in ACTG1 causes isolated ocular coloboma

Ocular coloboma (OC) is a defect in optic fissure closure and is a common cause
of severe congenital visual impairment. Bilateral OC is primarily genetically determined and shows marked locus heterogeneity. Whole exome sequencing was used to analyse twelve trios (child affected with OC and both unaffected parents), This identified de novo mutations in ten different genes in eight probands. Three of these genes encoded proteins associated with actin cytoskeleton dynamics: ACTG1, TWF1 and LCP1. Proband-only whole exome sequencing identified a second unrelated individual with isolated OC carrying the same ACTG1 allele, encoding p.(Pro70Leu). Both individuals have normal neurodevelopment with no extra-ocular signs of Baraitser Winter syndrome. We found this mutant protein to be incapable of incorporation into F-actin. The LCP1 and TWF1 variants each resulted in only minor disturbance of actin-interactions and no further plausibly causative variants were identified in these genes on re-sequencing 380 unrelated individuals with OC.