Gene/Protein Disease Symptom Drug Enzyme Compound
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Noonan Syndrome (NS) is characterised by short stature, typical facial dysmorphology and congenital heart defects. The incidence of NS is estimated to be between 1:1000 and 1:2500 live births. The main facial features of NS are hypertelorism with down-slanting palpebral fissures, ptosis and low-set posteriorly rotated ears with a thickened helix. The cardiovascular defects most commonly associated with this condition are pulmonary stenosis and hypertrophic cardiomyopathy. Other associated features are webbed neck, chest deformity, mild intellectual deficit, cryptorchidism, poor feeding in infancy, bleeding tendency and lymphatic dysplasias. The syndrome is transmitted as an autosomal dominant trait. In approximately 50% of cases, the disease is caused by missense mutations in the PTPN11 gene on chromosome 12, resulting in a gain of function of the non-receptor protein tyrosine phosphatase SHP-2 protein. Recently, mutations in the KRAS gene have been identified in a small proportion of patients with NS. A DNA test for mutation analysis can be carried out on blood, chorionic villi and amniotic fluid samples. NS should be considered in all foetuses with polyhydramnion, pleural effusions, oedema and increased nuchal fluid with a normal karyotype. With special care and counselling, the majority of children with NS will grow up and function normally in the adult world. Management should address feeding problems in early childhood, evaluation of cardiac function and assessment of growth and motor development. Physiotherapy and/or speech therapy should be offered if indicated. A complete eye examination and hearing evaluation should be performed during the first few years of schooling. Preoperative coagulation studies are indicated. Signs and symptoms lessen with age and most adults with NS do not require special medical care.
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PMID:Noonan syndrome. 1722 57

RASopathies are autosomal dominant disorders caused by mutations in more than 10 known genes that regulate the RAS/MAPK pathway. Noonan syndrome (NS) is a RASopathy characterized by a distinctive facial appearance, musculoskeletal abnormalities, and congenital heart defects. We have recently identified mutations in RIT1 in patients with NS. To delineate the clinical manifestations in RIT1 mutation-positive patients, we further performed a RIT1 analysis in RASopathy patients and identified 7 RIT1 mutations, including two novel mutations, p.A77S and p.A77T, in 14 of 186 patients. Perinatal abnormalities, including nuchal translucency, fetal hydrops, pleural effusion, or chylothorax and congenital heart defects, are observed in all RIT1 mutation-positive patients. Luciferase assays in NIH 3T3 cells demonstrated that the newly identified RIT1 mutants, including p.A77S and p.A77T, and the previously identified p.F82V, p.T83P, p.Y89H, and p.M90I, enhanced Elk1 transactivation. Genotype-phenotype correlation analyses of previously reported NS patients harboring RIT1, PTPN11, SOS1, RAF1, and KRAS revealed that hypertrophic cardiomyopathy (56 %) was more frequent in patients harboring a RIT1 mutation than in patients harboring PTPN11 (9 %) and SOS1 mutations (10 %). The rates of hypertrophic cardiomyopathy were similar between patients harboring RIT1 mutations and patients harboring RAF1 mutations (75 %). Short stature (52 %) was less prevalent in patients harboring RIT1 mutations than in patients harboring PTPN11 (71 %) and RAF1 (83 %) mutations. These results delineate the clinical manifestations of RIT1 mutation-positive NS patients: high frequencies of hypertrophic cardiomyopathy, atrial septal defects, and pulmonary stenosis; and lower frequencies of ptosis and short stature.
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PMID:Spectrum of mutations and genotype-phenotype analysis in Noonan syndrome patients with RIT1 mutations. 2671 97

Cardiofaciocutaneous (CFC) syndrome is one of the developmental disorders caused by a dysregulation of the Ras/mitogen-activated protein kinase (MAPK) pathway. RASopathies share overlapping clinical features, making the diagnosis challenging, especially in the newborn period. The majority of CFC syndrome cases arise by a mutation in the BRAF, MAP2K1, MAP2K2, or (rarely) KRAS genes. Germline KRAS mutations are identified in a minority of CFC and Noonan syndrome cases. Here, we describe a patient with a KRAS mutation presenting with a CFC syndrome phenotype. The female patient was referred for genetic testing because of congenital exophthalmos. Her facial appearance is distinctive with a coarse face, exophthalmos, ptosis, downslanting palpebral fissures, hypertelorism, deep philtrum, downturned corners of the mouth, and a short neck. She suffered from feeding difficulties, poor weight gain, and developmental delay. The sequencing of the genes involved in the MAPK pathway (PTPN11, SOS1, RAF1, KRAS, NRAS, MAP2K1, SHOC2, CBL, and SPRED1) identified a heterozygous de novo NM_004985.4:c.173C>T (p.Thr58Ile) in the KRAS gene. Germline KRAS mutations have been identified in approximately 2% of the reported NS cases and less than 5% of the reported CFC syndrome cases. Because CFC and Noonan syndrome share clinical overlapping features, the phenotype caused by KRAS mutations is often difficult to assign to one of the 2 entities. The mutation that we detected in our patient was previously reported in a patient with an Noonan syndrome phenotype. However, our patient predominantly exhibits CFC clinical features. In our case, coarse facial appearance and severe developmental delay help discriminate CFC from Noonan syndrome. Thus, patient follow-up, especially for delayed motor milestones suspected from RASopathies, is important for the discrimination of overlapping conditions as in the abovementioned syndromes.
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PMID:Cardiofaciocutaneous Syndrome Phenotype in a Case with de novo KRAS Pathogenic Variant. 3202 10