Weaver syndrome is a condition that involves tall stature with or without a large head size (macrocephaly), a variable degree of intellectual disability (usually mild), and characteristic facial features. These features can include a broad forehead; widely spaced eyes (hypertelorism); large, low-set ears; a dimpled chin, and a small lower jaw (micrognathia).

People with Weaver syndrome can also have joint deformities called contractures that restrict the movement of affected joints. The contractures may particularly affect the fingers and toes, resulting in permanently bent digits (camptodactyly). Other features of this disorder can include abnormal curvature of the spine (kyphoscoliosis); muscle tone that is either reduced (hypotonia) or increased (hypertonia); loose, saggy skin; and a soft-outpouching around the belly-button (umbilical hernia). Some affected individuals have abnormalities in the folds (gyri) of the brain, which can be seen by medical imaging; the relationship between these brain abnormalities and the intellectual disability associated with Weaver syndrome is unclear.

Researchers suggest that people with Weaver syndrome may have an increased risk of developing cancer, in particular a slightly increased risk of developing a tumor called neuroblastoma in early childhood, but the small number of affected individuals makes it difficult to determine the exact risk.

Weaver syndrome is usually caused by mutations in the EZH2 gene. The EZH2 gene provides instructions for making a type of enzyme called a histone methyltransferase. Histone methyltransferases modify proteins called histones, which are structural proteins that attach (bind) to DNA and give chromosomes their shape. By adding a molecule called a methyl group to histones (methylation), histone methyltransferases can turn off the activity of certain genes, which is an essential process in normal development. It is unclear how mutations in the EZH2 gene result in the abnormalities characteristic of Weaver syndrome.

Normal Function

The EZH2 gene provides instructions for making a type of enzyme called a histone methyltransferase. Histone methyltransferases modify proteins called histones, which are structural proteins that attach (bind) to DNA and give chromosomes their shape. By adding a molecule called a methyl group to histones (methylation), histone methyltransferases can turn off (suppress) the activity of certain genes, an essential process in normal development. Specifically, the EZH2 enzyme forms part of a protein group called the polycomb repressive complex-2. By turning off particular genes, this complex is involved in the process that determines the type of cell an immature cell will ultimately become (cell fate determination).

Health Conditions Related to Genetic Changes

Weaver syndrome

More than 30 EZH2 gene mutations have been identified in people with Weaver syndrome, which involves tall stature, a variable degree of intellectual disability (usually mild), and characteristic facial features. These features can include a broad forehead; widely spaced eyes (hypertelorism); large, low-set ears; a dimpled chin; and a small lower jaw (micrognathia). Some affected individuals have a large head size (macrocephaly). Most of the EZH2 gene mutations associated with Weaver syndrome change single protein building blocks (amino acids) in the EZH2 enzyme; others insert or delete small amounts of genetic material from the EZH2 gene, leading to production of an altered EZH2 enzyme. It is unclear how these EZH2 gene mutations result in the abnormalities characteristic of Weaver syndrome.

Prostate cancer

MedlinePlus Genetics provides information about Prostate cancer

Cancers

Changes in the EZH2 gene have been associated with various types of cancers. Mutations of this gene have been identified in cancers of blood-forming tissues (lymphomas and leukemias). These mutations are described as "gain-of-function" because they appear to enhance the activity of the EZH2 enzyme or give the enzyme a new, atypical function. In addition, excessive activity (overexpression) of the EZH2 gene has been identified in cancerous tumors of the prostate, breast, and other parts of the body. Changes involving the EZH2 gene likely impair normal control of cell division (proliferation), allowing cells to grow and divide too fast or in an uncontrolled way and leading to the development of cancer.

Other Names for This Gene

• enhancer of zeste homolog 2 (Drosophila)
• ENX-1
• EZH2_HUMAN
• histone-lysine N-methyltransferase EZH2
• KMT6
• KMT6A
• lysine N-methyltransferase 6

Genomic Location

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most cases result from new mutations in the gene and occur in people with no history of the disorder in their family. In a small number of cases, an affected person inherits the mutation from one affected parent.

The prevalence of Weaver syndrome is unknown. About 50 affected individuals have been described in the medical literature.