Noonan syndrome

What is Noonan syndrome?

Noonan syndrome is a developmental disorder characterized by unusual facial characteristics, short stature, heart defects, bleeding problems, and skeletal malformations. Eye abnormalities 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 occurs in approximately 1 in 1,000 to 2,500 people.

What genes are related to Noonan syndrome?

Mutations in the KRAS and PTPN11 genes cause Noonan syndrome.

Approximately 50 percent of individuals with Noonan syndrome have mutations in the PTPN11 gene. A small number of people with a severe or atypical type of Noonan syndrome have mutations in the KRAS gene. Individuals with KRAS mutations may show signs of other disorders that resemble Noonan syndrome, specifically cardiofaciocutaneous syndrome and Costello syndrome. These disorders are usually caused by changes in genes other than KRAS. Researchers are investigating whether these syndromes are distinct from each other or variations of the same disorder.

The PTPN11 gene provides instructions for making a protein that is important for the proper formation of several types of tissue during development. This protein also plays a role in cell division, cell specialization (the process by which cells mature to carry out specific functions), and cell movement. The KRAS gene provides instructions for making a protein that is also involved in cell growth and division, cell specialization, and tissue development.

Mutations in either the PTPN11 gene or the KRAS gene cause the resulting protein to be continuously active, rather than switching on and off in response to signals that control growth and development. This constant activation causes the improper regulation of systems that control cell growth and division, leading to the characteristic features 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 in each cell is sufficient to cause the disorder.

In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.

Noonan Syndrome on Wikipedia

'''Noonan Syndrome''' (NS) is a relatively common congenital genetic condition which affects both males and females. The principal features include congenital heart malformation, short stature, learning problems, indentation of the chest, impaired blood cloting, and a characteristic configuration of facial features. NS is one of the most common conditions associated with congenital heart anomalies, especially those of the right heart. The syndrome is named after Dr Jacqueline Noonan, a pediatric cardiology based in Kentucky. It is believed that 1 in 1,000 to 1 in 2,500 children worldwide are born with Noonan syndrome. It is one of the most common genetic syndromes associated with congenital heart malformations, similar in frequency to Down syndrome. However, the body features are much less obviously abnormal, and many if not most affected persons go undiagnosed.

Cause

Recurrence in siblings and apparent transmission from parent to child has long suggested a genetic defect with autosomal dominant inheritance and variable expression. A clearly affected person had up to a 50% chance of transmitting it to a child. The fact that affected parents cannot be identified for many children with Noonan syndrome suggests that (1) a parent could carry the gene without being affected, (2) that manifestations were variably expressed and could be so subtle as to go unrecognized, (3) that a high proportion of cases represented new, sporadic mutations, or (4) that Noonan syndrome is heterogeneous, comprised of more than one similar condition of differing cause, some not inherited. In most of the families with multiple affected members, Noonan syndrome mapped to chromosome 12q24.1 In 2001, it was reported that approximately half of a group of patients with Noonan syndrome carried a mutation of the ''PTPN11'' gene at that location, which encodes protein tyrosine phosphatase SHP-2 (Tartaglia M, et al. Nature Genetics 2001;29:465-468). ... [ Read More ]

External Resources

The Noonan Syndrome Support Group - Information about this organization as well the disease itself. Offers news, events, a survey, a newsletter and further resources.

National Library of Medicine - Includes the alternate names, a summary and a list of major features for Noonan syndrome.

The CaF Directory - A description of Noonan syndrome, its inheritance patterns and pre-natal diagnosing.

eMedicine - Noonan Syndrome : Article by Jennifer Ibrahim, MD - Thorough summary of history, diagnosis, and treatment.

Noonan Syndrome - Story of 6-year-old Becky, with factsheet and resources.

NORD - Noonan Syndrome - Offers the synonyms, a general discussion and further resources.

Noonan Syndrome - by Michelle Ellis - Account of her life with the disorder.

Birth Defects Foundation: Noonan Syndrome - History of the Foundation's involvement with Noonan's. Printable booklet and newsletter.

Martha Kate Downey - Support and information about Asperger's Syndrome, Noonan Syndrome, autism, and other disorders.

Noonan France - Association Française du syndrome de Noonan. Informations, contacts et té�moignages sur le syndrome de Noonan.

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