Noonan Syndrome

What is Noonan syndrome?

Noonan syndrome is a developmental disorder characterised by unusual facial characteristics, short stature, heart defects, bleeding problems, and skeletal malformations. Eye abnormalities can occur in up to 95 percent of patients. Problems with language and speech are common. Most males with this disorder have undescended testicles (cryptorchidism). The majority of children diagnosed with Noonan syndrome have normal intelligence, but a small percentage have special educational needs, and some affected individuals are mildly mentally retarded.

How common is Noonan syndrome?

Noonan syndrome has an incidence of 1 in 1,000 to 2,500 live births.

What genes are related to Noonan syndrome?

Mutations in the PTPN11 gene cause Noonan syndrome.

More than 50 percent of individuals with Noonan syndrome have changes in the PTPN11 gene. Researchers are investigating other genes that might be involved in this syndrome.

The PTPN11 gene makes a protein that is important for the proper formation of tissues during development. This protein also plays a role in cell division, cell specialization, and cell movement. Most mutations in the PTPN11 gene cause the protein to be continuously active, rather than switching on and off. The constant activation causes the improper regulation of systems that control cell functions such as growth and division. This misregulation leads to the signs and symptoms of Noonan syndrome.

How do people inherit Noonan syndrome?

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene is sufficient to cause the disorder.

In 30 percent to 75 percent of cases, one parent has Noonan syndrome. In other cases, affected individuals have a new mutation that is not present in either parent.

What other names do people use for Noonan syndrome?

• familial Turner syndrome
• Female Pseudo-Turner Syndrome
• Male Turner Syndrome
• Noonan-Ehmke syndrome
• pseudo-Ullrich-Turner syndrome
• Turner-like syndrome
• Turner's phenotype, karyotype normal
• Turner syndrome in female with X chromosome
• Ullrich-Noonan syndrome