CDK19 and Nystagmus: Indeed, the single described disruption (caused by a chromosomal inversion) of the CDK8 paralog CDK19 was associated with a different phenotype that comprised microcephaly, congenital bilateral falciform retinal folds, nystagmus, and learning disability;55 however, the functions of CDK8 and CDK19 are known to be divergent.56