Our lab was the first to publish that constitutional mutations in the epigenetic regulator EZH2 cause Weaver Syndrome (WS). WS is characterised by overgrowth, increased height, large head, intellectual disability and susceptibility to various cancers. We found pathogenic mutations in EZH2 among 7 out of 45 individuals with Weaver-like features, of which two had developed malignancies prior to referral. Our efforts focus on determining characteristics that will help us predict the likelihood of WS patients developing cancer, through phenotype/genotype correlations and functional studies. As of yet, it is not clear whether screening for haematological malignancies in patients with Weaver syndrome would increase the patients’ chances of survival.

Given that EZH2 is a histone-modifying enzyme known to be mutated in various somatic cancers, we hypothesised that constitutional mutations in other epigenetic regulators could explain the overgrowth features seen in our undiagnosed patients. To investigate this, we carried out whole exome sequencing in patients with paediatric syndromes similar to WS who did not have coding mutations in EZH2.

We have identified novel de novo mutations in EZH2’s partner protein EED in two patients to date. Both proteins are members of the Polycomb Repressive Complex 2 that maintains gene silencing. Based on the similarities of the patients’ phenotypes to WS, and on other lines of evidence including mouse Eed hypomorphs and an epigenetic signature that clustered with Weaver syndrome patients, we characterised these mutations as pathogenic. Here we describe additional features of overgrowth associated with constitutional mutations in human EED, which is also mutated somatically in various cancers. Samples from additional families are required to make a definitive link between mutations in these genes, Weaver-like syndromes, and cancer development. We continue to perform exome sequencing in patients with Weaver-like syndromes who have normal microarray studies and no mutations in EZH2 or NSD1.