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Ezh2 mutations found in the Weaver overgrowth syndrome cause a partial loss of H3K27 histone methyltransferase activity.

Ezh2 mutations found in the Weaver overgrowth syndrome cause a partial loss of H3K27 histone methyltransferase activity.
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Lui JC, Barnes KM, Dong L, Yue S, Graber E, Rapaport R, Dauber A, Nilsson O, Baron J,


Lui JC, Barnes KM, Dong L, Yue S, Graber E, Rapaport R, Dauber A, Nilsson O, Baron J, (click to view)

Lui JC, Barnes KM, Dong L, Yue S, Graber E, Rapaport R, Dauber A, Nilsson O, Baron J,

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The Journal of clinical endocrinology and metabolism 2017 12 13() doi 10.1210/jc.2017-01948
Abstract
Context
Weaver syndrome is characterized by tall stature, advanced bone age, characteristic facies, and variable intellectual disability. It is caused by heterozygous mutations in EZH2, a histone methyltransferase responsible for H3K27 trimethylation. However, no early truncating mutations have been identified, suggesting that null mutations do not cause Weaver syndrome.

Objective
To test alternative hypotheses that EZH2 variants found in Weaver syndrome either cause a gain of function or a partial loss of function.

Design
Exome sequencing was performed in a boy with tall stature, advanced bone age, and mild dysmorphic features. Mutant or wild-type EZH2 protein was expressed in mouse growth plate chondrocytes with or without endogenous EZH2, and enzymatic activity was measured. A mouse model was generated, and histone methylation was assessed in heterozygous and homozygous embryos.

Results
A de novo missense EZH2 mutation (c.1876G>A (p.Val626Met)) was identified in the proband. When expressed in growth plate chondrocytes, the mutant protein showed decreased histone methyltransferase activity. A mouse model carrying this EZH2 mutation was generated using CRISPR/Cas9. Homozygotes showed perinatal lethality while heterozygotes were viable, fertile, and showed mild overgrowth. Both homozygous and heterozygous embryos showed decreased H3K27 methylation.

Conclusion
We generated a mouse model with the same mutation as our patient and found that it recapitulates the Weaver overgrowth phenotype, and demonstrated that EZH2 mutations found in Weaver syndrome cause a partial loss of function.

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