Refractory thrombocytopenia could be a rare initial presentation of Noonan syndrome in newborn infants: a case report and literature review

Background

Noonan syndrome (NS) is a relatively rare inherited disease. Typical clinical presentation is important for the diagnosis of NS. But the initial presentation of NS could be significant variant individually which results in the difficult of working diagnosis. Here we report a rare neonatal case of NS who presented with refractory thrombocytopenia as the initial manifestation.

Case presentation

This was a preterm infant with refractory thrombocytopenia of unknown origin transferred from obstetric hospital at 6 weeks of age. During hospitalization, typical phenotypes of NS in addition to thrombocytopenia were observed, such as typical facial characteristics, short stature, atrial septal defect, cryptochidism, coagulation defect and chylothorax. Genetic testing showed a pathogenic variant at exon 2 of the PTPN11 gene with c.124A > G (p.T42A). Respiratory distress was deteriorated with progressive chylothorax. Chest tube was inserted for continuous draining. Chemical pleurodesis with erythromycin was tried twice, but barely effective. Finally, parents decided to withdraw medical care and the patient died.

Conclusions

Thrombocytopenia could be the first symptom of Noonan syndrome. After ruling out other common causes of thrombocytopenia, NS should be considered as the working diagnosis.

Allosteric Inhibitors of SHP2: An Updated Patent Review (2015-2020)

Srchomology-2-domain-containing PTP 2 (SHP2) is a nonreceptor phosphatase encoded by the PTPN11 gene. Over expression of SHP2 is associated with various human diseases, such as Noonan syndrome, LEOPARD syndrome, and cancers. To overcome the shortcomings of existing orthosteric inhibitors, novel inhibitors targeting the allosteric site of SHP2 with high selectivity and low toxicity are under development. This paper reviews allosteric inhibitors of SHP2 published in patents from 2015 to 2020. The molecules are classified according to the chemical structure of the central core. SHP2 has long been considered as an 'undruggable' protein. Fortunately, a critical breakthrough was made by researchers from Novartis AG Ltd., who identified SHP099 as a highly potent, selective, soluble, and orally bioavailable SHP2 allosteric inhibitor. Currently, there are several allosteric inhibitors of SHP2 in clinical development. However, drug resistance is still a major challenge. The combination of SHP2 allosteric inhibitors and immunotherapy drugs or molecular targeted drugs is emerging as a promising therapeutic strategy against drug resistance.

SHP-2 in Lymphocytes' Cytokine and Inhibitory Receptor Signaling

Somewhat counterintuitively, the tyrosine phosphatase SHP-2 (SH2 domain-containing protein tyrosine phosphatase-2) is crucial for the activation of extracellular signal-regulated kinase (ERK) downstream of various growth factor receptors, thereby exerting essential developmental functions. This phosphatase also deploys proto-oncogenic functions and specific inhibitors have recently been developed. With respect to the immune system, the role of SHP-2 in the signaling of cytokines relevant for myelopoiesis and myeloid malignancies has been intensively studied. The function of this phosphatase downstream of cytokines important for lymphocytes is less understood, though multiple lines of evidence suggest its importance. In addition, SHP-2 has been proposed to mediate the suppressive effects of inhibitory receptors (IRs) that sustain a dysfunctional state in anticancer T cells. Molecules involved in IR signaling are of potential pharmaceutical interest as blockade of these inhibitory circuits leads to remarkable clinical benefit. Here, we discuss the dichotomy in the functions ascribed to SHP-2 downstream of cytokine receptors and IRs, with a focus on T and NK lymphocytes. Further, we highlight the importance of broadening our understanding of SHP-2′s relevance in lymphocytes, an essential step to inform on side effects and unanticipated benefits of its therapeutic blockade.

[PTPN11 and the deafness]

Summary PTPN11 gene encodes tyrosine phosphatase SHP-2 which locates on chromosome 12（12q24.1）, expresses in most embryonic and adult tissues, and plays pivotal roles in cell proliferation, differentiation, survival and cell death. SHP-2 apparently participates in signaling events downstream of RAS-MAPK and JAK/STAT. Diseases related to PTPN11 gene mutations include the Noonan syndrome（NS） and the NS with Multiple Lentigines（NSML）. Both NS and NSML contain the phenotypes of deafness, craniofacial anomalies, short stature, congenital heart defects, skin disorders, ophthalmologic abnormalities and cancer predisposition.

Noonan syndrome: Severe phenotype and PTPN11 mutations

INTRODUCTION AND OBJECTIVE

Noonan syndrome (NS) is a genetic disorder characterized by a wide range of distinctive features and health problems. It caused in 50% of cases by missense mutations in PTPN11 gene. It has been postulated that it is possible to predict the disease course based into the impact of mutations on the protein.

PATIENTS AND METHODS

We report two cases of severe NS phenotype including hydrops fetalis. PTPN11 gene was studied in germinal cells of both patients by sequencing.

RESULTS

Two different mutations (p.Gly503Arg and p.Met504Val) was detected in PTPN11 gene.

DISCUSSION

These mutations have been reported previously, and when they were germinal variants, patients presented classic NS, NS with other malignancies and recently, p.Gly503Arg has been also observed in a patient with severe NS and hydrops fetalis, as our cases. Therefore, these observations shade light on that it is not always possibly to determine the genotype-phenotype relation based into the impact of mutations on the protein in NS patients with PTPN11 mutations.

LEOPARD Syndrome with PTPN11 Gene Mutation Showing Six Cardinal Symptoms of LEOPARD

LEOPARD multiple congenital anomaly syndrome inherited in an autosomal dominant manner. LEOPARD is an acronym for Lentigines, Eletrocardiographic conduction defects, Ocular hypertelorism, Pulmonary valve stenosis, Abnormalities of the genitalia, Retardation of growth, and Deafness. Clinical diagnosis is primarily based on multiple lentigines, typical facial features, and the presence of hypertrophic cardiomyopathy and/or café-au-lait macules. We report a typical case of LEOPARD syndrome with PTPN11 gene mutation associated with lentigines, electrocardiograph abnormality, ocular hypertelorism, pulmonary valve stenosis, growth retardation, and sensorineural hearing loss.

A case of Noonan syndrome and Whipple’s disease in the same patient

We report the first known case of both Noonan syndrome and Whipple’s disease occurring in the same patient. A 36-year-old female with history of Noonan syndrome developed fatigue, anorexia, arthritis of the knees and hands with a diffuse hyperpigmented rash, night sweats, and an unintentional fifteen pound weight loss over 4 mo. Small bowel enteroscopy demonstrated mild edematous yellowish mucosa without friability. Random small bowel biopsies revealed extensive periodic acid-Schiff positive material within the foamy macrophages. She was treated with a 12 mo course of trimethoprim-sulfamethoxazole DS with clinical improvement to baseline status.