Novel nonsense GNAS mutation in a 14-month-old boy with plate-like osteoma cutis and medulloblastoma

Medulloblastoma in a child with osteoma cutis - a rare association due to loss of GNAS expression

OBJECTIVES

Inactivating GNAS mutations result in varied phenotypes depending on parental origin. Maternally inherited mutations typically lead to hormone resistance and Albright's hereditary osteodystrophy (AHO), characterised by short stature, round facies, brachydactyly and subcutaneous ossifications. Paternal inheritance presents with features of AHO or ectopic ossification without hormone resistance. This report describes the case of a child with osteoma cutis and medulloblastoma. The objective of this report is to highlight the emerging association between inactivating germline GNAS mutations and medulloblastoma, aiming to shed light on its implications for tumor biology and promote future development of targeted surveillance strategies to improve outcomes in paediatric patients with these mutations.

CASE PRESENTATION

A 12-month-old boy presented with multiple plaque-like skin lesions. Biopsy confirmed osteoma cutis, prompting genetic testing which confirmed a heterozygous inactivating GNAS mutation. At 2.5 years of age, he developed neurological symptoms and was diagnosed with a desmoplastic nodular medulloblastoma, SHH molecular group, confirmed by MRI and histology. Further analysis indicated a biallelic loss of GNAS in the tumor.

CONCLUSIONS

This case provides important insights into the role of GNAS as a tumor suppressor and the emerging association between inactivating GNAS variants and the development of medulloblastoma. The case underscores the importance of careful neurological assessment and ongoing vigilance in children with known inactivating GNAS variants or associated phenotypes. Further work to establish genotype-phenotype correlations is needed to inform optimal management of these patients.

Hedgehog signaling mechanism and role in cancer

Cell-cell communication through evolutionarily conserved signaling pathways governs embryonic development and adult tissue homeostasis. Deregulation of these signaling pathways has been implicated in a wide range of human diseases including cancer. One such pathway is the Hedgehog (Hh) pathway, which was originally discovered in Drosophila and later found to play a fundamental role in human development and diseases. Abnormal Hh pathway activation is a major driver of basal cell carcinomas (BCC) and medulloblastoma. Hh exerts it biological influence through a largely conserved signal transduction pathway from the activation of the GPCR family transmembrane protein Smoothened (Smo) to the conversion of latent Zn-finger transcription factors Gli/Ci proteins from their repressor (GliR/CiR) to activator (GliA/CiA) forms. Studies from model organisms and human patients have provided deep insight into the Hh signal transduction mechanisms, revealed roles of Hh signaling in a wide range of human cancers, and suggested multiple strategies for targeting this pathway in cancer treatment.

Diagnostic and Prognostic Implications of GNAS Inactivation in Sonic Hedgehog-Activated Medulloblastoma: Case Report with Comprehensive Molecular Profiling and Review of Literature

SHH medulloblastoma from GNAS mutation (molecular profiling confirmation) with osteoma cutis & syndromic features.

A Case of Surgical Removal of a Giant and Multiple Acquired Plate-Like Osteoma Cutis After Implantation of a Dilator

Osteoma cutis (OC) is a group of rare skin ossification diseases, most of which are secondary to inflammation, scarring, trauma, or tumors, but a small portion are primary. Plate-like osteoma cutis is rare, especially after puberty. This report documents a case of a 30-year-old female, who presented with multiple stone-hard plates on the forehead and bilateral temples, with no relevant family history, or abnormalities in metabolism. These lesions showed slow progression over the last 11 years. The pathological diagnosis confirmed osteoma cutis. The forehead lesions were treated surgically due to aesthetic problems. In addition, long-term follow-up and observations are still needed to determine progression to deeper levels of tissue.

Gαs-Protein Kinase A (PKA) Pathway Signalopathies: The Emerging Genetic Landscape and Therapeutic Potential of Human Diseases Driven by Aberrant Gαs-PKA Signaling

Many of the fundamental concepts of signal transduction and kinase activity are attributed to the discovery and crystallization of cAMP-dependent protein kinase, or protein kinase A. PKA is one of the best-studied kinases in human biology, with emphasis in biochemistry and biophysics, all the way to metabolism, hormone action, and gene expression regulation. It is surprising, however, that our understanding of PKA's role in disease is largely underappreciated. Although genetic mutations in the PKA holoenzyme are known to cause diseases such as Carney complex, Cushing syndrome, and acrodysostosis, the story largely stops there. With the recent explosion of genomic medicine, we can finally appreciate the broader role of the Gαs-PKA pathway in disease, with contributions from aberrant functioning G proteins and G protein-coupled receptors, as well as multiple alterations in other pathway components and negative regulators. Together, these represent a broad family of diseases we term the Gαs-PKA pathway signalopathies. The Gαs-PKA pathway signalopathies encompass diseases caused by germline, postzygotic, and somatic mutations in the Gαs-PKA pathway, with largely endocrine and neoplastic phenotypes. Here, we present a signaling-centric review of Gαs-PKA-driven pathophysiology and integrate computational and structural analysis to identify mutational themes commonly exploited by the Gαs-PKA pathway signalopathies. Major mutational themes include hotspot activating mutations in Gαs, encoded by GNAS, and mutations that destabilize the PKA holoenzyme. With this review, we hope to incite further study and ultimately the development of new therapeutic strategies in the treatment of a wide range of human diseases. SIGNIFICANCE STATEMENT: Little recognition is given to the causative role of Gαs-PKA pathway dysregulation in disease, with effects ranging from infectious disease, endocrine syndromes, and many cancers, yet these disparate diseases can all be understood by common genetic themes and biochemical signaling connections. By highlighting these common pathogenic mechanisms and bridging multiple disciplines, important progress can be made toward therapeutic advances in treating Gαs-PKA pathway-driven disease.

Progressive Osseous Heteroplasia is not an Autosomal Dominant Trait but Reflects Superimposed Mosaicism in Different GNAS Inactivation Disorders

Progressive osseous heteroplasia (POH) is a rarely occurring genetic condition characterized by severe segmental ossification involving the skin and deep connective tissues including the muscles. So far, the disorder is generally described as an autosomal dominant trait. By contrast, the following arguments are in favor of the alternative concept that POH should rather be taken as a non-specific segmental manifestation of different GNAS inactivation disorders such as Albright hereditary osteodystrophy (AHO) with hormone resistance, AHO without hormone resistance, and osteomatosis cutis. Presently, POH has got its own OMIM number 166350 but this is obviously wrong because the disorder does not reflect heterozygosity for a GNAS mutation. Conversely, the disorder is most likely due to an early event of postzygotic loss of heterozygosity with loss of the corresponding wild-type allele. This alternative concept, as proposed in 2016, offers a plausible explanation for the following features of POH. Familial occurrence is usually absent. POH is usually observed in families with one of the three GNAS inactivation disorders as mentioned above. Mosaicism is suggested by the pronounced segmental manifestation of POH and by its lateralization. Some patients have, in addition to POH, bilaterally disseminated features of osteomatosis cutis or AHO, and other patients have family members with one of these nonsegmental disorders. Remarkably, POH tends to appear much earlier than the nonsegmental GNAS inactivation disorders. - Molecular support of the concept was documented in a superficial variant of POH called 'plate-like osteoma cutis'. In several other autosomal dominant skin disorders, molecular corroboration of the theory of superimposed mosaicism has been provided. - For all of these reasons, it is unlikely that POH can further be taken as a distinct autosomal dominant trait. Generation of more molecular data in multiple cases of POH occurring in GNAS inactivation disorders will be crucial to corroborate the proposed concept.

Biallelic loss of GNAS in a patient with pediatric medulloblastoma

Genome sequencing was performed on matched normal and tumor tissue from a 6.5-yr-old boy with a diagnosis of recurrent medulloblastoma. A pathogenic heterozygous c.432+1G>A canonical splice donor site variant in GNAS was detected on analysis of blood DNA. Analysis of tumor DNA showed the same splice variant along with copy-neutral loss of heterozygosity on Chromosome 20 encompassing GNAS, consistent with predicted biallelic loss of GNAS in the tumor specimen. This case strengthens the evidence implicating GNAS as a tumor-suppressor gene in medulloblastoma and highlights a scenario in which therapeutics targeting the cAMP pathway may be of great utility.

Single-Cell Transcriptomics in Medulloblastoma Reveals Tumor-Initiating Progenitors and Oncogenic Cascades during Tumorigenesis and Relapse

Progenitor heterogeneity and identities underlying tumor initiation and relapse in medulloblastomas remain elusive. Utilizing single-cell transcriptomic analysis, we demonstrated a developmental hierarchy of progenitor pools in Sonic Hedgehog (SHH) medulloblastomas, and identified OLIG2-expressing glial progenitors as transit-amplifying cells at the tumorigenic onset. Although OLIG2⁺ progenitors become quiescent stem-like cells in full-blown tumors, they are highly enriched in therapy-resistant and recurrent medulloblastomas. Depletion of mitotic Olig2⁺ progenitors or Olig2 ablation impeded tumor initiation. Genomic profiling revealed that OLIG2 modulates chromatin landscapes and activates oncogenic networks including HIPPO-YAP/TAZ and AURORA-A/MYCN pathways. Co-targeting these oncogenic pathways induced tumor growth arrest. Together, our results indicate that glial lineage-associated OLIG2⁺ progenitors are tumor-initiating cells during medulloblastoma tumorigenesis and relapse, suggesting OLIG2-driven oncogenic networks as potential therapeutic targets.

GPCR-Hippo Signaling in Cancer

The Hippo signaling pathway is involved in tissue size regulation and tumorigenesis. Genetic deletion or aberrant expression of some Hippo pathway genes lead to enhanced cell proliferation, tumorigenesis, and cancer metastasis. Recently, multiple studies have identified a wide range of upstream regulators of the Hippo pathway, including mechanical cues and ligands of G protein-coupled receptors (GPCRs). Through the activation related G proteins and possibly rearrangements of actin cytoskeleton, GPCR signaling can potently modulate the phosphorylation states and activity of YAP and TAZ, two homologous oncogenic transcriptional co-activators, and major effectors of the Hippo pathway. Herein, we summarize the network, regulation, and functions of GPCR-Hippo signaling, and we will also discuss potential anti-cancer therapies targeting GPCR-YAP signaling.

Diagnosis and management of pseudohypoparathyroidism and related disorders: first international Consensus Statement

This Consensus Statement covers recommendations for the diagnosis and management of patients with pseudohypoparathyroidism (PHP) and related disorders, which comprise metabolic disorders characterized by physical findings that variably include short bones, short stature, a stocky build, early-onset obesity and ectopic ossifications, as well as endocrine defects that often include resistance to parathyroid hormone (PTH) and TSH. The presentation and severity of PHP and its related disorders vary between affected individuals with considerable clinical and molecular overlap between the different types. A specific diagnosis is often delayed owing to lack of recognition of the syndrome and associated features. The participants in this Consensus Statement agreed that the diagnosis of PHP should be based on major criteria, including resistance to PTH, ectopic ossifications, brachydactyly and early-onset obesity. The clinical and laboratory diagnosis should be confirmed by a molecular genetic analysis. Patients should be screened at diagnosis and during follow-up for specific features, such as PTH resistance, TSH resistance, growth hormone deficiency, hypogonadism, skeletal deformities, oral health, weight gain, glucose intolerance or type 2 diabetes mellitus, and hypertension, as well as subcutaneous and/or deeper ectopic ossifications and neurocognitive impairment. Overall, a coordinated and multidisciplinary approach from infancy through adulthood, including a transition programme, should help us to improve the care of patients affected by these disorders.

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

The G protein Gαs acts as a tumor suppressor in sonic hedgehog signaling-driven tumorigenesis

G protein-coupled receptors (GPCRs) are critical players in tumor growth and progression. The redundant roles of GPCRs in tumor development confound effective treatment; therefore, targeting a single common signaling component downstream of these receptors may be efficacious. GPCRs transmit signals through heterotrimeric G proteins composed of Gα and Gβγ subunits. Hyperactive Gαs signaling can mediate tumor progression in some tissues; however, recent work in medulloblastoma and basal cell carcinoma revealed that Gαs can also function as a tumor suppressor in neoplasms derived from ectoderm cells including neural and epidermal stem/progenitor cells. In these stem-cell compartments, signaling through Gαs suppresses self-renewal by inhibiting the Sonic Hedgehog (SHH) and Hippo pathways. The loss of GNAS, which encodes Gαs, leads to activation of these pathways, over-proliferation of progenitor cells, and tumor formation. Gαs activates the cAMP-dependent protein kinase A (PKA) signaling pathway and inhibits activation of SHH effectors Smoothened-Gli. In addition, Gαs-cAMP-PKA activation negatively regulates the Hippo pathway by blocking the NF2-LATS1/2-Yap signaling. In this review, we will address the novel function of the signaling network regulated by Gαs in suppression of SHH-driven tumorigenesis and the therapeutic approaches that can be envisioned to harness this pathway to inhibit tumor growth and progression.

Hedgehog Signal Transduction: Key Players, Oncogenic Drivers, and Cancer Therapy

The Hedgehog (Hh) signaling pathway governs complex developmental processes, including proliferation and patterning within diverse tissues. These activities rely on a tightly regulated transduction system that converts graded Hh input signals into specific levels of pathway activity. Uncontrolled activation of Hh signaling drives tumor initiation and maintenance. However, recent entry of pathway-specific inhibitors into the clinic reveals mixed patient responses and thus prompts further exploration of pathway activation and inhibition. In this review, we share emerging insights into regulated and oncogenic Hh signaling, supplemented with updates on the development and use of Hh pathway-targeted therapies.

Progressive osseous heteroplasia is not a Mendelian trait but a type 2 segmental manifestation of GNAS inactivation disorders: A hypothesis

Progressive osseous heteroplasia (POH) is a segmental disorder characterized by progressive heterotopic ossification that extends from dermal and subcutaneous tissues to deeper structures. So far, it has been taken as a rarely occurring bone disease with autosomal dominant inheritance. Here, arguments are presented in favor of the alternative concept that the disorder is merely a type 2 segmental manifestation of autosomal dominant GNAS inactivation disorders. Type 2 segmental mosaicism arises, in a heterozygous embryo, from a somatic mutational event that occurs at an early developmental stage, resulting in loss of the corresponding wild-type allele and giving rise to a homozygous or hemizygous cell clone. As a characteristic feature, such type 2 segmental involvement is far more pronounced than the type 1 segmental mosaicism as noted in otherwise healthy individuals. The concept of type 2 segmental mosaicism has been proven at the molecular level in six human traits including neurofibromatosis 1, Hailey-Hailey disease, and Gorlin syndrome. In POH, molecular proof of principle is so far lacking. The following lines of reasoning, however, support the hypothesis that POH can be explained by a similar mechanism. Firstly, POH has been found to be associated with different phenotypes caused by inactivating GNAS mutations, which is why it cannot be categorized as one distinct Mendelian trait. Secondly, POH occurs as a rather rare complication of these autosomal dominant traits, which is not compatible with the assumption of a separate Mendelian disorder. Thirdly, in a case of plate-like osteoma that represents a more superficial variant of POH, molecular proof of the concept of type 2 segmental manifestation has already been provided, and the available literature suggests that POH can be best explained by a similar mechanism. Moreover, findings obtained in animal experiments support the assumption that human POH represents such superimposed segmental manifestation of GNAS inactivation disorders.

G-Protein Gαs controls medulloblastoma initiation by suppressing sonic hedgehog signaling

We identify Gαs as a novel tumor suppressor in medulloblastoma that functions principally by inhibition of sonic hedgehog signaling. Gαs not only stimulates cyclic adenosine monophosphate (cAMP)-dependent signaling but also inhibits ciliary trafficking of hedgehog components. Elevation of cAMP inhibits medulloblastoma growth and augments inhibition of smoothened to decrease tumor cell proliferation, thus highlighting Gαs as a potential therapeutic target.

GNAS mutations in Pseudohypoparathyroidism type 1a and related disorders

Pseudohypoparathyroidism type 1a (PHP1a) is characterized by hypocalcaemia and hyperphosphatemia due to parathyroid hormone resistance, in association with the features of Albright's hereditary osteodystrophy (AHO). PHP1a is caused by maternally inherited inactivating mutations of Gs-alpha, which is encoded by a complex imprinted locus termed GNAS. Paternally inherited mutations can lead either to pseudopseudohypoparathyroidism (PPHP) characterized by AHO alone, or to progressive osseous heteroplasia (POH), characterized by severe heterotopic ossification. The clinical aspects and molecular genetics of PHP1a and its related disorders are reviewed together with the 343 kindreds with Gs-alpha germline mutations reported so far in the literature. These 343 (176 different) mutations are scattered throughout the 13 exons that encode Gs-alpha and consist of 44.9% frameshift, 28.0% missense, 14.0% nonsense, and 9.0% splice-site mutations, 3.2% in-frame deletions or insertions, and 0.9% whole or partial gene deletions. Frameshift and other highly disruptive mutations were more frequent in the reported 37 POH kindreds than in PHP1a/PPHP kindreds (97.3% vs. 68.7%, P < 0.0001). This mutation update and respective genotype-phenotype data may be of use for diagnostic and research purposes and contribute to a better understanding of these complex disorders.

The G protein α subunit Gαs is a tumor suppressor in Sonic hedgehog-driven medulloblastoma

Medulloblastoma, the most common malignant childhood brain tumor, exhibits distinct molecular subtypes and cellular origins. Genetic alterations driving medulloblastoma initiation and progression remain poorly understood. Herein, we identify GNAS, encoding the G-protein Gsα, as a potent tumor suppressor gene that defines a subset of aggressive Sonic Hedgehog (Shh)-driven human medulloblastomas. Ablation of the single Gnas gene in anatomically-distinct progenitors is sufficient to induce Shh-associated medulloblastomas, which recapitulate their human counterparts. Gsα is highly enriched at the primary cilium of granule neuron precursors and suppresses Shh-signaling by regulating both the cAMP-dependent pathway and ciliary trafficking of Hedgehog pathway components. Elevation of a Gsα effector, cAMP, effectively inhibits tumor cell proliferation and progression in Gnas mutants. Thus, our gain- and loss-of-function studies identify a previously unrecognized tumor suppressor function for Gsα that acts as a molecular link across Shh-group medulloblastomas of disparate cellular and anatomical origins, illuminating G-protein modulation as a potential therapeutic avenue.