Clinical characteristics: EZH2-related overgrowth is a variable overgrowth syndrome characterized by tall stature, macrocephaly, variable intellect (ranging from normal intellect to severe intellectual disability), characteristic facial appearance, and a range of associated clinical features including advanced bone age, poor coordination, soft, doughy skin, camptodactyly of the fingers and/or toes, umbilical hernia, abnormal tone, and hoarse, low cry in infancy. Brain MRI has identified abnormalities in a few individuals with EZH2-related overgrowth. Neuroblastoma occurs at a slightly increased frequency in individuals with a heterozygous EZH2 pathogenic variant, but data are insufficient to determine absolute risk. There is currently no evidence that additional malignancies (including hematologic malignancies) occur with increased frequency, though a few have been reported.

Diagnosis/testing: The diagnosis of EZH2-related overgrowth is based on detection of a heterozygous germline EZH2 pathogenic variant on molecular genetic testing.

Management: Treatment of manifestations: For individuals with developmental delay and/or learning disability, referral for learning/behavior/speech assessment and support may be indicated. Occasionally, toe camptodactyly may require surgical release. Physiotherapy may be of benefit to those experiencing joint pain secondary to ligamentous laxity or joint contractures. Standard treatment with appropriate specialist referral(s) is indicated for epilepsy, scoliosis, and other clinical issues.

Surveillance: Regular medical follow up of young children with EZH2-related overgrowth to monitor developmental progress, camptodactyly (for resolution/improvement), and/or hypotonia; medical follow up of older children/teenagers who do not have medical complications may be less frequent. If scoliosis is present, monitoring per the recommendations of an orthopedist. Although current data do not support specific tumor surveillance programs, clinicians should have a low threshold for investigating any possible tumor-related symptoms.

Pregnancy management: Families and their health care providers should be made aware that an affected baby may be large so that appropriate delivery plans can be made.

Genetic counseling: EZH2-related overgrowth is inherited in an autosomal dominant manner. Some individuals diagnosed with EZH2-related overgrowth have an affected parent; some individuals diagnosed with EZH2-related overgrowth have the disorder as the result of a de novo EZH2 pathogenic variant. The proportion of individuals with EZH2-related overgrowth caused by a de novo pathogenic variant is unknown. Each child of an individual with EZH2-related overgrowth has a 50% chance of inheriting the pathogenic variant; the phenotype in individuals who inherit a familial EZH2 pathogenic variant cannot be predicted. Once the pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.