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The EZH2, EED, and SUZ12genes encode proteins that comprise core components of the polycomb repressive complex 2 (PRC2), an epigenetic “writer” with H3K27 methyltransferase activity, catalyzing the addition of up to three methyl groups on histone 3 at lysine residue 27 (H3K27). Partial loss‐of‐function variants in genes encoding the EZH2 and EED subunits of the complex lead to overgrowth, macrocephaly, advanced bone age, variable intellectual disability, and distinctive facial features. EZH2‐associated overgrowth, caused by constitutional heterozygous mutations within Enhancer of Zeste homologue 2(EZH2), has a phenotypic spectrum ranging from tall stature without obvious intellectual disability or dysmorphic features to classical Weaver syndrome (OMIM #277590). EED‐associated overgrowth (Cohen–Gibson syndrome; OMIM #617561) is caused by germline heterozygous mutations in Embryonic Ectoderm Development(EED), and manifests overgrowth and intellectual disability (OGID), along with other features similar to Weaver syndrome. Most recently, rare coding variants in SUZ12have also been described that present with clinical characteristics similar to the previous two syndromes. Here we review the PRC2 complex and clinical syndromes of OGID associated with core components EZH2, EED, and SUZ12.

The Polycomb repressive complex 2 is an epigenetic writer and recruiter with a role in transcriptional silencing. Constitutional pathogenic variants in its component proteins have been found to cause two established overgrowth syndromes: Weaver syndrome (EZH2‐related overgrowth) and Cohen‐Gibson syndrome (EED‐related overgrowth). Imagawa et al. (2017) initially reported a singleton female with a Weaver‐like phenotype with a rare coding SUZ12variant—the same group subsequently reported two additional affected patients. Here we describe a further 10 patients (from nine families) with rare heterozygous SUZ12variants who present with a Weaver‐like phenotype. We report four frameshift, two missense, one nonsense, and two splice site variants. The affected patients demonstrate variable pre‐ and postnatal overgrowth, dysmorphic features, musculoskeletal abnormalities and developmental delay/intellectual disability. Some patients have genitourinary and structural brain abnormalities, and there may be an association with respiratory issues. The addition of these 10 patients makes a compelling argument that rare pathogenic SUZ12variants frequently cause overgrowth, physical abnormalities, and abnormal neurodevelopmental outcomes in the heterozygous state. Pathogenic SUZ12variants may be de novo or inherited, and are sometimes inherited from a mildly‐affected parent. Larger samples sizes will be needed to elucidate whether one or more clinically‐recognizable syndromes emerge from different variant subtypes.