Mutations in the PTPN11 gene, which encodes the protein tyrosine phosphatase Shp2, cause Noonan syndrome and LEOPARD syndrome, inherited multifaceted diseases including cardiac and vascular defects.
A human induced pluripotent stem cell (iPSC) line was generated using peripheral blood mononuclear cells (PBMCs) from a patient with NSML that carries a gene mutation of p.Q510P on the PTPN11 gene using non-integrating Sendai virus technique.
Different mechanisms of disease have been demonstrated to be associated with the two classes of PTPN11 mutations underlying Noonan syndrome and Noonan syndrome with multiple lentigines (also known as LEOPARD syndrome).
Catalytically activating mutations in <i>Ptpn11</i>, which encodes the protein tyrosine phosphatase SHP2, cause 50% of Noonan syndrome (NS) cases, whereas inactivating mutations in <i>Ptpn11</i> are responsible for nearly all cases of the similar, but distinct, developmental disorder Noonan syndrome with multiple lentigines (NSML; formerly called LEOPARD syndrome).
Comparisons between clinical presentations showed that SASH1-related phenotypes can exhibit hyper- and hypopigmentation on the trunk and extremities, similar to dyschromatosis, while scattered café au-lait spots usually appeared in PTPN11-related LEOPARD syndrome.
We report a patient with Noonan syndrome with multiple lentigines (NSML) due to a PTPN11 (p.Thr468Met) mutation associated with hypertrophic neuropathy of lumbar plexus in an adult woman, initially referred for neuropathic pain.
We report a patient with Noonan syndrome with multiple lentigines (NSML) due to a PTPN11 (p.Thr468Met) mutation associated with hypertrophic neuropathy of lumbar plexus in an adult woman, initially referred for neuropathic pain.
Deviation of the SHP2 catalytic activity from a certain range, either too strong or too weak, may therefore lead to similar clinical outcomes in NS and LS, possibly through an imbalanced Wnt signal caused by inadequate dephosphorylation of parafibromin.
In in vitro assays, melanin synthesis in human melanoma cells expressing SHP-2 with LS-associated mutations was higher than in cells expressing normal SHP-2, suggesting that LS-associated SHP-2 mutations might enhance melanin synthesis in melanocytes, and that the activation of Akt/mTOR signalling may contribute to this process.
Exome sequencing revealed a pathogenic de novo germline variant in the PTPN11 gene (c.1529A>G; p.(Gln510Arg)), which has so far been associated with Noonan, as well as LEOPARD syndrome.
In the boy, progressive HCM was diagnosed during the first week of life and a diagnosis of NSML was established at age 20 weeks by showing a heterozygous Q510E mutation in PTPN11.
Moreover, human activating and inactivating mutations of SHP2 are responsible for two related developmental disorders called Noonan and LEOPARD Syndromes, respectively, which are both characterized, in part, by congenital heart defects.
In in vitro assays, melanin synthesis in human melanoma cells expressing SHP-2 with LS-associated mutations was higher than in cells expressing normal SHP-2, suggesting that LS-associated SHP-2 mutations might enhance melanin synthesis in melanocytes, and that the activation of Akt/mTOR signalling may contribute to this process.
We hereby report a heterozygous de novo mutation in the PTPN11 gene (c.1403C > T) manifesting with a clinical picture of LS during childhood, and later development of neuropathic pain with hypertrophic plexi, which are typically observed in NF1 but have not been reported in LS.
In the second part, we describe the different PTPN11 mutation-associated pathologies and their clinical manifestations, with particular focus on the biochemical and signaling outcomes of NS and NS-ML-associated mutations, and on the recent advances regarding the pathophysiology of these diseases.