PTPN11 mutations in Noonan syndrome type I: detection of recurrent mutations in exons 3 and 13

Protein-tyrosine phosphatase, nonreceptor type 11 mutation analysis and clinical assessment in 45 patients with Noonan syndrome

We report on PTPN11 (protein-tyrosine phosphatase, nonreceptor type 11) mutation analysis and clinical assessment in 45 patients with Noonan syndrome. Sequence analysis was performed for all of the coding exons 1-15 of PTPN11, revealing a novel 3-bp deletion mutation and 10 recurrent missense mutations in 18 patients. Clinical assessment showed that 1) the growth pattern was similar in mutation-positive and mutation-negative patients, with no significant difference in birth length [-0.6 +/- 2.2 sd (n = 10) vs. -0.6 +/- 1.4 sd (n = 21); P = 0.95], childhood height [-2.6 +/- 1.1 sd (n = 14) vs. -2.1 +/- 1.6 sd (n = 23); P = 0.28], or target height [-0.4 +/- 0.9 sd (n = 14) vs. -0.2 +/- 0.7 sd (n = 17); P = 0.52]; 2) pulmonary valve stenosis was more frequent in mutation-positive patients than in mutation-negative patients (10 of 18 vs. 6 of 27; P = 0.02), as was atrial septal defect (10 of 18 vs. 4 of 27; P = 0.005), whereas hypertrophic cardiomyopathy was present in five mutation-negative patients only; and 3) other features were grossly similar in the prevalence between mutation-positive and mutation-negative patients, but hematological abnormalities, such as bleeding diathesis and juvenile myelomonocytic leukemia, were exclusively present in mutation-positive patients (5 of 18 vs. 0 of 27; P = 0.007). The results suggest that PTPN11 mutations account for approximately 40% of Noonan syndrome patients, as has been reported previously. Furthermore, assessment of clinical features, in conjunction with data reported previously, implies that the type of cardiovascular lesions and the occurrence of hematological abnormalities are different in mutation-positive and mutation-negative patients, whereas the remaining findings are similar in the two groups of patients.

LEOPARD syndrome: a new polyaneurysm association and an update on the molecular genetics of the disease

LEOPARD syndrome, one of many cardiocutaneous syndromes, is an acronym for some of the obvious manifestations of the disease, such as lentigines or ocular hypertelorism. The synonymous name progressive cardiomyopathic lentiginosis better indicates the morbid cardiac features that patients with the syndrome have. A patient with LEOPARD syndrome is presented. He had recurrent upper extremity aneurysms requiring multiple operations and finally PTFE reinforced venous grafts to prevent further aneurysmal degeneration. He has multiple other peripheral aneurysms, thus far asymptomatic. His diagnosis of LEOPARD syndrome was confirmed on a genetic basis. Review of the literature reveals no previous reports of severe aneurysmal disease in these patients.

Genotype-phenotype correlations in Noonan syndrome

OBJECTIVE

To study genotype-phenotype correlations in a cohort of clinically well-characterized pediatric patients with Noonan syndrome (NS). Study design Fifty-seven unrelated patients with the clinical diagnosis of NS ascertained according to standardized inclusion criteria were prospectively enrolled. Mutational analysis was performed by direct sequencing of the entire coding sequence of the PTPN11 gene.

RESULTS

Sixteen known and 3 novel PTPN11 mutations could be detected in 60% of index patients, in all familial and in 52% of the sporadic cases. Presence of pulmonic stenosis, short stature, easy bruising, and thorax deformities was significantly associated with a PTPN11 mutation, whereas cardiomyopathy was more common in patients without a mutation. On average, PTPN11 mutation-negative probands fulfilled fewer clinical criteria of NS, but more than half-among them all with cardiomyopathy-had the full clinical picture of NS indistinguishable from typical cases with PTPN11 mutation.

CONCLUSIONS

The phenotype of NS due to PTPN11 mutations is clinically unambiguous in the majority of patients and represents a highly penetrant trait. Individuals with the clinical diagnosis of NS but without a PTPN11 mutation presumably represent a heterogeneous group in which patients with cardiomyopathy appear to constitute an interesting subgroup for future research.

Noonan syndrome-associated SHP2/PTPN11 mutants cause EGF-dependent prolonged GAB1 binding and sustained ERK2/MAPK1 activation

Noonan syndrome is a developmental disorder with dysmorphic facies, short stature, cardiac defects, and skeletal anomalies, which can be caused by missense PTPN11 mutations. PTPN11 encodes Src homology 2 domain-containing tyrosine phosphatase 2 (SHP2 or SHP-2), a protein tyrosine phosphatase that acts in signal transduction downstream to growth factor, hormone, and cytokine receptors. We compared the functional effects of three Noonan syndrome-causative PTPN11 mutations on SHP2's phosphatase activity, interaction with a binding partner, and signal transduction. All SHP2 mutants had significantly increased basal phosphatase activity compared to wild type, but that activity varied significantly between mutants and was further increased after epidermal growth factor stimulation. Cells expressing SHP2 mutants had prolonged extracellular signal-regulated kinase 2 activation, which was ligand-dependent. Binding of SHP2 mutants to Grb2-associated binder-1 was increased and sustained, and tyrosine phosphorylation of both proteins was prolonged. Coexpression of Grb2-associated binder-1-FF, which lacks SHP2 binding motifs, blocked the epidermal growth factor-mediated increase in SHP2's phosphatase activity and resulted in a dramatic reduction of extracellular signal-regulated kinase 2 activation. Taken together, these results document that Noonan syndrome-associated PTPN11 mutations increase SHP2's basal phosphatase activity, with greater activation when residues directly involved in binding at the interface between the N-terminal Src homology 2 and protein tyrosine phosphatase domains are altered. The SHP2 mutants prolonged signal flux through the RAS/mitogen-activated protein kinase (ERK2/MAPK1) pathway in a ligand-dependent manner that required docking through Grb2-associated binder-1 (GAB1), leading to increased cell proliferation.

A 3-bp deletion mutation ofPTPN11 in an infant with severe Noonan syndrome including hydrops fetalis and juvenile myelomonocytic leukemia

A de novo 3-bp deletion (179-181delGTG) was identified at exon 3 of the PTPN11 gene in a female infant with severe Noonan phenotype including hydrops fetalis and juvenile myelomonocytic leukemia. Since the 3-bp deletion is predicted to result in loss of the 60th glycine in the N-SH2 domain that is directly involved in the intramolecular interaction between the N-SH2 and the PTP domains of the PTPN11 protein, this mutation would disrupt the N-SH2/PTP binding in the absence of a phosphopeptide, leading to an excessive phosphatase activity. The results expand the spectrum of PTPN11 mutations in Noonan syndrome (NS), and suggest that a PTPN11 mutation leads to a wide range of clinical features of Noonan syndrome.

Endothelial lineage-mediated loss of the GATA cofactor Friend of GATA 1 impairs cardiac development

GATA transcription factors, together with Friend of GATA (FOG) cofactors, are required for the differentiation of diverse cell types. Multiple aspects of hematopoiesis are controlled by the interaction of FOG-1 with the GATA-1/2/3 subfamily. Likewise, FOG-2 is coexpressed with the GATA-4/5/6 subfamily at other sites, including the heart and gonads. FOG-2 and GATA-4 are required for cardiac development. Through transgenic rescue of hematopoietic defects of FOG-1-/- embryos we define an unsuspected role for FOG-1 in heart development. In particular, rescued FOG-1-/- mice die at embryonic day (E) 14.5 with cardiac defects that include double outlet right ventricle and a common atrioventricular valve. Using conditional inactivation of Fog-1 we assign the cell of origin in which FOG-1 function is required. Neural crest cells migrate properly into FOG-1-/- hearts and mice with FOG-1 conditionally excised from neural crest derivatives fail to develop cardiac abnormalities. In contrast, conditional inactivation of FOG-1 in endothelial-derived tissues by means of Tie-2-expressed Cre recapitulates the rescue-knockout defects. These findings establish a nonredundant requirement for FOG-1 in the outlet tract and atrioventricular valves of the heart that depend on expression in endothelial-derived tissue and presumably reflect cooperation with the GATA-4/5/6 subfamily.

Blocking the function of tyrosine phosphatase SHP-2 by targeting its Src homology 2 domains

SHP-2 is an Src homology 2 (SH2) domain-containing tyrosine phosphatase with crucial functions in cell signaling and major pathological implications. It stays inactive in the cytosol and is activated by binding through its SH2 domains to tyrosine-phosphorylated receptors on the cell surface. One such cell surface protein is PZR, which contains two tyrosine-based inhibition motifs responsible for binding of SHP-2. We have generated a glutathione S-transferase fusion protein carrying the tandem tyrosine-based inhibition motifs of PZR, and the protein was tyrosine-phosphorylated by co-expressing c-Src in Escherichia coli cells. The purified phosphoprotein displays a strong binding to SHP-2 and causes its activation in vitro. However, when introduced into NIH 3T3 cells by using a protein delivery reagent, it effectively inhibited the activation of ERK1/2 induced by growth factors and serum but not by phorbol ester, in reminiscence of the effects caused by expression of dominant negative SHP-2 mutants and deletion of functional SHP-2. The data suggest that the exogenously introduced PZR protein specifically binds SHP-2, blocks its translocation, and renders it functionally incompetent. This is further supported by the fact that the phosphorylated PZR protein had no inhibitory effects on fibroblasts derived from mice expressing only a mutant SHP-2 protein lacking most of the N-terminal SH2 domain. This study thus provides a novel and highly specific method to interrupt the function of SHP-2 in cells.