Genome-wide sequencing expands the phenotypic spectrum of EP300 variants

Many disease genes are defined by their role in causing specific clinically recognizable syndromes. Heterozygous loss of function of the gene EP300 is responsible for a minority of cases of Rubinstein-Taybi syndrome (RSTS). With the application of whole-exome sequencing and whole-genome sequencing, there is the potential to discover new genotype-phenotype correlations. The purpose of this case series is to describe three unrelated females without classic manifestations of RSTS who were unexpectedly found on genome-wide sequencing to have likely pathogenic variants in EP300. These individuals expand our knowledge of the disease spectrum by virtue of their very rare or novel clinical features. Results are placed within the context of all prior published EP300 cases not ascertained by targeted testing, which are disproportionately female compared with a cohort identified because of a clinical suspicion of RSTS (p = 0.01). There are implications for diagnosis, management, and genetic counselling of individuals with EP300-related disease.