How Does Noonan Syndrome Affect The Body & What Triggers It?

Children have various congenital lesions, some of which are considered fairly common. However, there are rare diseases that have a low prevalence. Many people may get severely affected by these rare syndromes. One such pathology is Noonan syndrome. (1)

Noonan syndrome is a hereditary pathology. The mutated PTPN11 gene from the parent carrying it is transmitted to the offspring. As a rule, men are barren, thus, the gene is transmitted through the maternal system. Usually, the familial nature of this disease is noted and in rare cases, hereditary relations can not be established.

Noonan syndrome is a genetic abnormality that causes several physical abnormalities, usually short stature, abnormal heart structure, and abnormal appearance.

Noonan syndrome can be inherited, but it can also be caused by mutations that occur naturally in children with their parents having normal genes. One of several different genes is involved in this disorder and it occurs in about 1 in every 1000 to 2500 people. So it can be regarded as relatively common and occurs in both boys and girls (no gender viability or preference). (2)

How Does Noonan Syndrome Affect The Body?

Noonan syndrome is most often accompanied by cardiovascular disorders. Against the background of the pathology, lung stem stenosis (stenosis) and ventricular septal defect are revealed.

The second place is occupied by genitourinary abnormalities. Thus, the kidney reveals defects such as growth failure (tissue development failure) or one kidney missing. In adolescent patients, both kidneys may be normal or completel9y defective.

Girls often have delayed menstruation and boys are completely devoid of the spermatic function of the testicles. There is also spermatogenesis dysfunction and in many cases, sperm is completely absent.

A bleeding disorder is also common as Noonan syndrome often affects the blood system. Problem with circulation or increased bleeding during cuts and surgery is usually associated with the disorder.

In some patients, abnormalities in mental developmental can be easily detected.

Other Symptoms Of Noonan Syndrome:

Common symptoms of the disease include abnormalities in blood vessels, abnormal lower pinna (lower ear), heart disorders, high palate, pterygium, shorter fourth finger (ring finger), upper eyelids hanging, and the wide space between the eyes.

Hearing impairment and intellectual disability may occur in some patients. Many individuals with this syndrome are short. In boys, testicular growth failure and “stationary testes” may occur. Both boys and girls are late in puberty, and young men with Noonan syndrome may experience low levels of testosterone in their blood and infertility. In girls, the onset of menstruation is usually delayed, but fertility is often maintained normally.

Cause Of Noonan Syndrome

In order for cells to grow and proliferate normally, many genes and proteins need to work together in a sequence and a typical manner. Normal cell growth/proliferation requires the function of a transmission pathway called the “RAS-MAPK signaling pathway”. Many genes and proteins are involved in this signal transduction pathway. In Noonan syndrome, the genes or proteins involved in this signal transduction pathway become abnormal.

As of 2019, the causative gene abnormality has not been completely elucidated. About 15% of patients do not have a causative gene abnormality, and it is assumed that there is an unknown genetic abnormality that can cause Noonan syndrome. (3)

In many patients with Noonan syndrome, the disease onset is sudden with no hereditary link. As a result, children may develop the illness, even if their parents are normal with no Noonan syndrome disorder. If you have a family case of Noonan syndrome, the causative genetic abnormality will be inherited, and there is a 50% chance that your child will develop Noonan syndrome.

Treatment Measures For Noonan Syndrome

There is no therapy to completely cure Noonan syndrome. However, some of the specific symptoms and abnormalities caused by this syndrome can be treated. Heart abnormalities are monitored and treated as necessary.

Growth hormone treatment can stimulate growth and somewhat correct the short stature of the patients. For boys with testicular hypoplasia, treatment with testosterone can help after sufficient growth. Testosterone promotes the development of a more masculine appearance. Young women may require estrogen therapy to develop common adult characteristics.

Children suspected of Noonan syndrome should be screened for heart disease and hearing impairment. (4) (5)

References:

  1. Roberts AE, Allanson JE, Tartaglia M, Gelb BD. Noonan syndrome. The Lancet. 2013;381(9863):333-342.
  2. Kruszka P, Porras AR, Addissie YA, et al. Noonan syndrome in diverse populations. American Journal of Medical Genetics Part A. 2017;173(9):2323-2334.
  3. Totoiu MO. Developmental and Neurological Features of Noonan Syndrome. Noonan Syndrome: Elsevier; 2019:93-111.
  4. Noonan JA. Noonan syndrome. Health Care for People with Intellectual and Developmental Disabilities across the Lifespan: Springer; 2016:827-832.
  5. Romano AA, Allanson JE, Dahlgren J, et al. Noonan syndrome: clinical features, diagnosis, and management guidelines. Pediatrics. 2010;126(4):746-759.

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