The applicant proposes to study Noonan syndrome (NS) and related disorders. NS is a relatively common autosomal dominant trait with features that include congenital heart disease (CHD), short stature, dysmorphism, and mental retardation. We recently showed that mutations in the PTPN1 1 gene cause NS. PTPN1 I encodes the protein tyrosine phosphatase, SHP-2, which has two src-homology 2 (SH2) domains. SHP-2 is known to play a critical role in receptor tyrosine kinase-mediated signal transduction through MAP kinase. These new findings provide opportunities to understand the role of SHP-2 in CHD as well as to identify additional CHD genes.To test the hypothesis that all PTPN11 mutations causing NS are missense defects affecting residues at the interface of the N-SH2 and phosphatase domains, we will identify and characterize PTPN11 mutations in a large, well-characterized NS cohort. This will establish the range of molecular defects and may permit correlation of genotype with phenotype. To determine whether PTPN1 I mutations cause Noonan-like syndromes and sporadic CHD, cohorts with the latter will be screened as will those with cardiofaciocutaneous and Costello syndromes.To test the hypothesis that PTPN1 1 mutations cause NS by a gain-of-function mechanism, the function of mutant SHP-2 proteins will be tested in cell culture to document that they have increased phosphatase activity, interact with the SHP-2 docking partners, and excessively stimulate receptor tyrosine kinase signaling cascades.To test whether NS mutations perturb the FGFR and EGFR pathways during development through a gain-offunction, NS mutations will be studied in Drosophila and Xenopus. Mutant corkscrew (the SHP-2 orthologue) will be introduced in fly embryos with null or hypomorphic corkscrew alleles. Development of terminal structures (torso pathway), eyes (sevenless pathway), wings (EGFR pathway) and trachea (FGFR pathway) will be assessed. Mutant SHP-2 will be expressed in frog animal caps to assess FGF-mediated mesoderm induction.Since NS is genetically heterogeneous, there are additional NS disease genes. To identify them, we will use candidate gene and positional cloning strategies. For the former, we will focus on genes with biological roles relevant to signaling cascades in which SHP-2 participates. For the latter, a positional cloning/candidacy approach will be used with multiplex NS kindreds whose trait does not link to the PTPN1 I locus.These studies will delineate the molecular diversity of PTPN1 1 mutations underlying NS and related disorders as well as provide insights into the effects of SHP-2 mutants at the biochemical, cellular, and organismal levels. The results will inform future work directed at understanding the pathogenesis of NS and at developing novel therapeutic strategies, such as those ameliorating the progression of cardiac hypertrophy.
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