Case Report: Association of Ocular Colobomas With a Novel Missense Variant in CDC42, a Member of the Rho Family of Small GTPases.

We present a 2-year-old male with bilateral iris and chorioretinal colobomas, speech delays, and facial and digital anomalies. Trio exome sequencing demonstrated a de novo, novel heterozygous variant, c.379G>A p.Glu127Lys in CDC42, conferring a diagnosis of Takenouchi-Kosaki syndrome. The p.Glu127Lys variant was not located in the same region as previously designated mutation classes for CDC42, and the patient's missense substitution was predicted to disrupt CDC42 interactions with Collybistin II and IQGAP1. As conditional knock-out mouse models have demonstrated coloboma in association with loss of Cdc42 expression, we conclude that the colobomas can be attributed to the CDC42 variant and that similar ocular anomalies are likely to be described with other Rho GTPases in the future.