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.

Terminal osseous dysplasia is an X-linked dominant male-lethal disease characterized by skeletal dysplasia of the limbs, pigmentary defects of the skin, and recurrent digital fibroma during infancy (Sun et al., 2010).

Desbuquois dysplasia, which belongs to the multiple dislocation group of disorders, is characterized by dislocations of large joints, severe pre- and postnatal growth retardation, joint laxity, and flat face with prominent eyes. Radiologic features include short long bones with an exaggerated trochanter that gives a 'monkey wrench' appearance to the proximal femur, and advanced carpal and tarsal ossification (summary by Bui et al., 2014). For a discussion of genetic heterogeneity of Desbuquois dysplasia, see DBQD1 (251450).

Autosomal dominant intellectual developmental disorder-66 (MRD66) is characterized by global developmental delay with mildly to moderately impaired intellectual development and mild speech delay. The phenotype and severity are highly variable. Some patients have behavioral problems or autism spectrum disorder, and about 50% have variable types of seizures. Additional features may include nonspecific dysmorphic facial features, tall or short stature, and mild skeletal anomalies (Rahimi et al., 2022).

Autosomal dominant intellectual developmental disorder-71 with behavioral abnormalities (MRD71) is a neurodevelopmental disorder characterized by global developmental delay with hypotonia, speech delay, and variably impaired cognitive development. Almost all affected individuals show marked behavioral manifestations, including autism spectrum disorder (ASD), ADHD, hypersensitivity, and aggression. Many have dysmorphic features, although there is not a common gestalt (Harris et al., 2021).

Autosomal dominant intellectual developmental disorder-73 (MRD73) is a highly variable neurodevelopmental disorder characterized by impaired intellectual development that ranges from mild to severe, speech delay, behavioral abnormalities, and nonspecific dysmorphic facial features (Janssen et al., 2022).