Changes in the STAT3 gene alter the structure and function of the STAT3 protein, impairing its ability to control the activity of other genes. The defective protein disrupts cellular functions such as immune system regulation. The resulting immune system abnormalities make people with AD-HIES highly susceptible to infections. The STAT3 protein is also involved in the formation of cells that build and break down bone tissue, which could explain why STAT3 gene mutations lead to the skeletal and dental abnormalities characteristic of AD-HIES. It remains unclear how STAT3 gene mutations lead to increased IgE levels.
When AD-HIES syndrome is not caused by STAT3 gene mutations, the genetic cause of is unknown.
This condition also affects other parts of the body, including the bones and teeth. Many people with this condition have skeletal abnormalities such as an unusually large range of joint movement (hyperextensibility), an abnormal curvature of the spine (scoliosis), reduced bone density (osteopenia), and a tendency for bones to fracture easily. Dental abnormalities are also common in AD-HIES. The primary (baby) teeth do not fall out at the usual time during childhood, but are retained as the adult teeth grow in. Other signs and symptoms of AD-HIES can include distinctive facial features and structural abnormalities of the brain, which typically do not affect a person's intelligence.
Autosomal dominant hyper IgE syndrome (AD-HIES) has an autosomal dominant pattern of inheritance. This means that one copy of an altered gene in each cell is sufficient to cause the disorder. In about half of all cases, an affected person inherits a STAT3 mutation from an affected parent. Other cases result from new mutations in this gene. These cases occur in people with no history of the disorder in their family.
A small percentage (<5%) of individuals who have the clinical symptoms associated with AD-HIES do not have an identifiable mutation in the STAT3 gene. This suggests that there are additional unidentified mutations.