Noonan Syndrome
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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 body tissues 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.
Source: National Institutes of Health
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Findings from University Children's Hospital broaden understanding of Noonan syndrome in children
2009 MAY 18 - (NewsRx.com) -- Research findings, 'Noonan syndrome, the Ras-MAPK signalling pathway and short stature,' are discussed in a new report. "Short stature, with a mean final height almost two standard deviations below the normal mean, is a major feature of Noonan syndrome. The biological basis of the growth failure is not yet clear," scientists in Tubingen, Germany report. "The recent detection of mutations in the protein tyrosine phosphatase, non-receptor type 11 gene (PTPN11) in half of all individuals with Noonan syndrome has opened up a new perspective from the endocrine point of view, since the tyrosine phosphatase SHP2 encoded by PTPN11 is implicated in the downregulation of growth hormone (GH) receptor signalling. Current data show decreased insulin-like growth factor (IGF)-I and IGF-binding protein 3 (IGFBP-3) levels in those children with Noonan syndrome who carry PTPN11 mutations. GH responsiveness seems to be reduced in the presence of PTPN11 mutations, but, so far, data are too scarce to draw any final conclusions. Children with Noonan or Noonan-related syndromes carrying mutations in components of the Ras-mitogen-activated protein kinase (MAPK) signalling pathway downstream from SHP2 also have short stature, though less frequently in the case of SOS1 mutations. Therefore, apart from the disturbance of GH signalling, there must be other relevant mechanisms that influence longitudinal growth in Noonan syndrome. In a small subgroup of patients with Noonan syndrome and Noonan-related syndromes, tumor risk is increased. This susceptibility is relevant when GH therapy is considered," wrote G. Binder and colleagues, University Children's Hospital. The researchers concluded: "Progress in the understanding of cell regulation by Ras-MAPK signalling and its interconnection with other pathways will hopefully provide evidence on which therapy might be helpful and which might be nocuous in the care of children with Noonan syndrome." Binder and colleagues published their study in Hormone Research (Noonan syndrome, the Ras-MAPK signalling pathway and short stature. Hormone Research, 2009;71 Suppl 2():64-70). For additional information, contact G. Binder, University Children's Hospital, Paediatric Endocrinology, Tubingen, Germany. The publisher's contact information for the journal Hormone Research is: S. Karger AG, Allschwilerstrasse 10, CH-4009 Basel, Switzerland. Keywords: Germany, Tubingen, Endocrine, Hormones, IGF I, Noonan Syndrome, Pediatrics, Phosphatase, Therapy, Treatment. This article was prepared by Biotech Business Week editors from staff and other reports. Copyright 2009, Biotech Business Week via NewsRx.com.
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