The mechanism through which novel single nucleotide variants lead to Noonan syndrome

• Main Authors: Hui-WenYu, 游惠雯
• Other Authors: Chen, Peng-Chieh
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/wzwt5x

碩士 === 國立成功大學 === 臨床醫學研究所 === 102 === Abstract Noonan Syndrome (NS), one of the most common developmental diseases, is an autosomal genetic disorder that may occur sporadically or be inherited. NS is caused by germline mutations in genes encoding RAS-ERK signaling pathway. NS, affected about 1 in 1000~2500 newborns, is characterized by developmental delay, short stature, typical facies, webbed neck, distinctive craniofacial dysmorphism, congenital heart diseases, variable cognitive deficits and neurocognitive delay. NS-causing mutations, which may cause hyperactive RAS-ERK signaling pathway, were identified in PTPN11, SOS1, RAF1, KRAS, CBL, SHOC2, NRAS and RIT1 genes in ~80% NS patients. However, the genetic causes in the remaining ~20% of NS patients are still unknown. Hence, whole exome sequencing was performed with genomic DNA from 24 NS patients who carry no mutations in the known NS genes. On average, 121 novel missense mutations were found per patient. Genes involved in RAS-ERK signaling pathway were surveyed and novel mutations in NF1, RASA, and RIT1genes were identified. NF1 and RASA2 genes encode RAS GTPase activating proteins (RASGAP) that negatively regulate RAS activity. RIT1 encodes small GTPase protein, which is a RAS subfamily protein. To validate the effects of mutant proteins, wild type (WT) and mutant NF1, RASA2, or RIT1 genes were expressed in HEK-293 cell lines and in Flp-In TREx 293 cell lines. Loss-of-function mutations of NF1 and RASA2 failed to suppress the RAS activity and gain-of-function mutation in RIT1 lead to ERK hyper-activation. These data suggest that NF1, RASA2, and RIT1 are candidates of NS-causing genes.