Overlapping phenotypes between SHORT and Noonan syndromes in patients with PTPN11 pathogenic variants

Insulin signaling and its application

The discovery of insulin in 1921 introduced a new branch of research into insulin activity and insulin resistance. Many discoveries in this field have been applied to diagnosing and treating diseases related to insulin resistance. In this mini-review, the authors attempt to synthesize the updated discoveries to unravel the related mechanisms and inform the development of novel applications. Firstly, we depict the insulin signaling pathway to explain the physiology of insulin action starting at the receptor sites of insulin and downstream the signaling of the insulin signaling pathway. Based on this, the next part will analyze the mechanisms of insulin resistance with two major provenances: the defects caused by receptors and the defects due to extra-receptor causes, but in this study, we focus on post-receptor causes. Finally, we discuss the recent applications including the diseases related to insulin resistance (obesity, cardiovascular disease, Alzheimer's disease, and cancer) and the potential treatment of those based on insulin resistance mechanisms.

SHORT Syndrome: an Update on Pathogenesis and Clinical Spectrum

PURPOSE OF REVIEW

This review describes the unique pathogenesis of SHORT syndrome, a rare genetic form of insulin resistance syndrome, and recent advances in understanding the underlying mechanisms. SHORT syndrome results from dysfunction of PI3K, but the mechanisms behind the clinical manifestations are not entirely understood. Elucidating these mechanisms may contribute to the understanding of the roles of insulin signaling and PI3K signaling in humans. There are paucity of data on treatment and outcomes.

RECENT FINDINGS

The clinical spectrum of the disorder appears wider than previously understood, and overlaps with other clinical syndromes. PI3K malfunction is associated with insulin resistance, decreased lipogenesis, increased energy expenditure, and possible IGF1 resistance. SHORT syndrome may be underdiagnosed, and should be considered in individuals with growth failure, craniofacial dysmorphism, and lipodystrophy. Much is still unknown about the optimal management and long-term outcomes.

The Tyrosine Phosphatase SHP2: A New Target for Insulin Resistance?

The SH2 containing protein tyrosine phosphatase 2(SHP2) plays essential roles in fundamental signaling pathways, conferring on it versatile physiological functions during development and in homeostasis maintenance, and leading to major pathological outcomes when dysregulated. Many studies have documented that SHP2 modulation disrupted glucose homeostasis, pointing out a relationship between its dysfunction and insulin resistance, and the therapeutic potential of its targeting. While studies from cellular or tissue-specific models concluded on both pros-and-cons effects of SHP2 on insulin resistance, recent data from integrated systems argued for an insulin resistance promoting role for SHP2, and therefore a therapeutic benefit of its inhibition. In this review, we will summarize the general knowledge of SHP2’s molecular, cellular, and physiological functions, explaining the pathophysiological impact of its dysfunctions, then discuss its protective or promoting roles in insulin resistance as well as the potency and limitations of its pharmacological modulation.

SHP2's gain-of-function in Werner syndrome causes childhood disease onset likely resulting from negative genetic interaction

Prompt diagnosis of complex phenotypes is a challenging task in clinical genetics. Whole exome sequencing has proved to be effective in solving such conditions. Here, we report on an unpredictable presentation of Werner Syndrome (WRNS) in a 12 year-old girl carrying a homozygous truncating variant in RECQL2, the gene mutated in WRNS, and a de novo activating missense change in PTPN11, the major Noonan syndrome gene, encoding SHP2, a protein tyrosine phosphatase positively controlling RAS function and MAPK signaling, which have tightly been associated with senescence in primary cells. All the major WRNS clinical criteria were present with an extreme precocious onset and were associated with mild intellectual disability, severe growth retardation and facial dysmorphism. Compared to primary fibroblasts from adult subjects with WRNS, proband's fibroblasts showed a dramatically reduced proliferation rate and competence, and a more accelerated senescence, in line with the anticipated WRNS features occurring in the child. In vitro functional characterization of the SHP2 mutant documented its hyperactive behavior and a significantly enhanced activation of the MAPK pathway. Based on the functional interaction of WRN and MAPK signaling in processes relevant to replicative senescence, these findings disclose a unique phenotype likely resulting from negative genetic interaction. This article is protected by copyright. All rights reserved.

Altered canonical and striatal-frontal resting state functional connectivity in children with pathogenic variants in the Ras/mitogen-activated protein kinase pathway

Mounting evidence supports the role of the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway in neurodevelopmental disorders. Here, the authors used a genetics-first approach to examine how Ras/MAPK pathogenic variants affect the functional organization of the brain and cognitive phenotypes including weaknesses in attention and inhibition. Functional MRI was used to examine resting state functional connectivity (RSFC) in association with Ras/MAPK pathogenic variants in children with Noonan syndrome (NS). Participants (age 4-12 years) included 39 children with NS (mean age 8.44, SD = 2.20, 25 females) and 49 typically developing (TD) children (mean age 9.02, SD = 9.02, 33 females). Twenty-eight children in the NS group and 46 in the TD group had usable MRI data and were included in final analyses. The results indicated significant hyperconnectivity for the NS group within canonical visual, ventral attention, left frontoparietal and limbic networks (p < 0.05 FWE). Higher connectivity within canonical left frontoparietal and limbic networks positively correlated with cognitive function within the NS but not the TD group. Further, the NS group demonstrated significant group differences in seed-based striatal-frontal connectivity (Z > 2.6, p < 0.05 FWE). Hyperconnectivity within canonical brain networks may represent an intermediary phenotype between Ras/MAPK pathogenic variants and cognitive phenotypes, including weaknesses in attention and inhibition. Altered striatal-frontal connectivity corresponds with smaller striatal volume and altered white matter connectivity previously documented in children with NS. These results may indicate delayed maturation and compensatory mechanisms and they are important for understanding the pathophysiology underlying cognitive phenotypes in NS and in the broader population of children with neurodevelopmental disorders.

Genetics of lipodystrophy syndromes

Lipodystrophic syndromes (LS) constitute a clinically and genetically heterogeneous group of diseases characterized by a loss of adipose tissue. These syndromes are usually associated with metabolic complications, which are determinant for morbidity and mortality. The classical forms of LS include partial, generalized, and progeroid lipodystrophies. They are usually due to defects in proteins playing a key role in adipogenesis and adipocyte functions. More recently, systemic disorders combining lipodystrophy and multiple organ dysfunction have been described, including autoinflammatory syndromes, mitochondrial disorders, as well as other complex entities. To date, more than thirty genes have been implicated in the monogenic forms of LS, but the majority of them remain genetically-unexplained. The associated pathophysiological mechanisms also remain to be clarified in many instances. Next generation sequencing-based approaches allow simultaneous testing of multiple genes and have become crucial to speed up the identification of new disease-causing genes. The challenge for geneticists is now the interpretation of the amount of available genetic data, generated especially by exome and whole-genome sequencing. International recommendations on the interpretation and classification of variants have been set up and are regularly reassessed. Very close collaboration between geneticists, clinicians, and researchers will be necessary to make rapid progress in understanding the molecular and cellular basis of these diseases, and to promote personalized medicine.

SHORT Syndrome: Systematic Appraisal of the Medical and Dental Phenotype

INTRODUCTION

SHORT syndrome is a rare autosomal dominant condition described by its acronym of short stature, hyperextensibility of joints and/or inguinal hernia, ocular depression, Rieger abnormality, and teething delay. Individuals have a distinct progeroid craniofacial appearance with a triangular face, frontal bossing, hypoplastic or thin alae nasi, large low-set ears, and mandibular retrognathia.

OBJECTIVES

To systematically appraise the literature and update the clinical phenotype with emphasis on the dental condition.

DESIGN

A systematic literature search was carried out to update the clinical phenotype, identifying reports of individuals with SHORT syndrome published after August 2015. The same search strategy but not limited to publication date was carried out to identify reports of the dental phenotype. Two independent reviewers screened 1937 articles with 55 articles identified for full-text review.

RESULTS

Nineteen individuals from 11 families were identified. Facial dysmorphism including ocular depression, triangular shaped face, frontal bossing, large low-set ears, and micrognathia were the most consistent features followed by lipodystrophy, insulin resistance, and intrauterine growth restriction. Teething delay, microdontia, hypodontia, and enamel hypoplasia have all been reported.

CONCLUSION

Features that comprise the SHORT acronym do not accurately or completely describe the clinical phenotype. The craniofacial appearance is one of the most consistent features. Lipodystrophy and insulin resistance may also be considered cardinal features. After teething delay, enamel hypoplasia and microdontia are the most common dental manifestations. We present recommendations for the dental and orthodontic/orthognathic management of individuals with SHORT syndrome.

Genetic Defects in Children with Cardiac Anomalies/Malformations: Noonan and CFC Syndromes

Cardiac defects presenting in childhood show significant phenotypic and genetic heterogeneity. With availability of advanced genetic technologies, these can be detected early using specialized testing. Prenatal testing is currently feasible with improved ultrasonography and fetal echocardiography. Here, we report two cases of Noonan's and cardiofaciocutaneous syndromes in patients seen in the genetic unit of a tertiary care center presenting with cardiac defect with or without developmental delay, short stature, and dysmorphism. In these conditions, there is also increased risk of malignancy such as juvenile myelomonocytic leukemia. With the advent of next-generation sequencing, definitive diagnosis and counseling is possible in this group of conditions.

Insulin resistance and exaggerated insulin sensitivity triggered by single-gene mutations in the insulin signaling pathway

Whereas the genetic basis of insulin sensitivity is determined by variation in multiple genes, mutations of single genes can give rise to profound changes in such sensitivity. Mutations of the insulin receptor gene (INSR)-which trigger type A insulin resistance, Rabson-Mendenhall, or Donohue syndromes-and those of the gene for the p85α regulatory subunit of phosphoinositide 3-kinase (PIK3R1), which give rise to SHORT syndrome, are the most common and second most common causes, respectively, of single-gene insulin resistance. Loss-of-function mutations of the genes for the protein kinase Akt2 (AKT2) or for TBC1 domain family member 4 (TBC1D4) have been identified in families with severe insulin resistance. Gain-of-function mutations of the gene for protein tyrosine phosphatase nonreceptor type 11 (PTPN11), which negatively regulates insulin receptor signaling, give rise to Noonan syndrome, and some individuals with this syndrome manifest insulin resistance. Gain-of-function mutations of the gene for the p110α catalytic subunit of phosphoinositide 3-kinase (PIK3CA) have been identified in individuals with segmental overgrowth or megalencephaly, some of whom also manifest spontaneous hypoglycemia. A gain-of-function mutation of AKT2 was also found in individuals with recurrent hypoglycemia. Loss-of-function mutations of the gene for phosphatase and tensin homolog (PTEN), another negative regulator of insulin signaling, give rise to Cowden syndrome in association with exaggerated metabolic actions of insulin. Clinical manifestations of individuals with such mutations of genes related to insulin signaling thus provide insight into the essential function of such genes in the human body.