Specific mosaicKRASmutations affecting codon 146 cause oculoectodermal syndrome and encephalocraniocutaneous lipomatosis

Encephalocraniocutaneous lipomatosis phenotype associated with mosaic biallelic pathogenic variants in the NF1 gene

Encephalocraniocutaneous lipomatosis (ECCL) is a sporadic congenital condition characterised by ocular, cutaneous and central nervous system involvement. Mosaic activating variants in FGFR1 and KRAS have been reported in several individuals with this syndrome. We report on a patient with neurofibromatosis type 1 (NF1) with a germline pathogenic variant in the NF1 gene and an ECCL phenotype, suggesting ECCL to be part of a spectrum of malformations associated with NF1 pathogenic variants. An anatomical hemispherectomy was performed for intractable epilepsy. Through genetic analysis of blood, cerebral tissue and giant cell lesions in both jaws, we identified the germline NF1 pathogenic variant in all samples and a second-hit pathogenic NF1 variant in cerebral tissue and both giant cell lesions. Both NF1 variants were located on different alleles resulting in somatic mosaicism for a biallelic NF1 inactivation originating in early embryogenesis (second-hit mosaicism or Happle type 2 mosaicism). The biallelic deficit in NF1 in the left hemicranium explains the severe localised, congenital abnormality in this patient. Identical first and second-hit variants in a giant cell lesion of both upper and lower jaws provide confirmatory evidence for an early embryonic second hit involving at least the neural crest. We suggest that the ECCL phenotype may be part of a spectrum of congenital problems associated with mosaic NF1 nullisomy originating during early embryogenesis. The biallelic NF1 inactivation during early embryogenesis mimics the severe activation of the RAS-MAPK pathway seen in ECCL caused by embryonic mosaic activating FGFR1 and KRAS variants in the cranial region. We propose that distinct mechanisms of mosaicism can cause the ECCL phenotype through convergence on the RAS-MAPK pathway.

Calcified Sclero-Choroidal Choristomas in Mosaic RASopathies: A Description of a New Imaging Sign

PURPOSE

To evaluate the imaging and clinical features of unusual calcified lesions seen in the fundus of patients with mosaic RASopathy.

DESIGN

Single-center retrospective observational study.

SUBJECTS

Ten eyes with calcified fundus lesions in 7 patients with mosaic RASopathy.

METHODS

The lesions were evaluated with fundus photography, oral fundus fluorescein angiography, B-scan ultrasonography, magnetic resonance imaging (MRI), and computed tomography (CT) scan where available.

MAIN OUTCOME MEASURES

The imaging characteristics of calcified fundus lesions were assessed.

RESULTS

We found 7 patients with mosaic RASopathies, 5 men and 2 women (3 with linear sebaceous nevus syndrome, 3 with oculoectodermal syndrome, and 1 with encephalocraniocutaneous lipomatosis) with molecular confirmation in 5 cases, all 5 having KRAS-pathogenic variants. Calcified fundus lesions were identified in 10 eyes (bilateral in 3 patients), appearing as slightly elevated, creamy-yellow lesions around or adjacent to the optic nerve, extending supero-nasally; all but 2 of these lesions involved both the choroid and sclera, with 2 of them only involving the sclera at the time of examination. One case developed a choroidal neovascular membrane necessitating intravitreal bevacizumab injections. All 7 patients had B-scan ultrasonography, and the lesion appeared as a hyperechogenic area with an acoustic shadow posteriorly despite reduced gain. Five patients had MRI, and where fundus lesions were present, there was a focal defect in the sclero-choroidal layer. Four patients had a CT scan, and all 4 showed calcifications affecting both the posteromedial sclero-choroid and adjacent medial rectus muscle. Two of these patients had normal eye movements, 1 had a unilateral fixed adducted eye and a vestigial fibrous medial rectus muscle seen in imaging and intraoperatively, and the fourth had marked exotropia with a right gaze deficit affecting both eyes.

CONCLUSIONS

We propose that the lesions seen in this cohort are calcified sclero-choroidal choristomas and should be suspected in mosaic RASopathies when creamy-yellow lesions are seen in the fundus. If identified, the possibility of choroidal neovascularization should be considered during follow-up. In all cases where a CT scan was performed, a novel sign of sclero-muscular calcification involving the medial rectus muscle was seen.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Mosaic RASopathies concept: different skin lesions, same systemic manifestations?

BACKGROUND

Cutaneous epidermal nevi are genotypically diverse mosaic disorders. Pathogenic hotspot variants in HRAS, KRAS, and less frequently, NRAS and BRAF may cause isolated keratinocytic epidermal nevi and sebaceous nevi or several different syndromes when associated with extracutaneous anomalies. Therefore, some authors suggest the concept of mosaic RASopathies to group these different disorders.

METHODS

In this paper, we describe three new cases of syndromic epidermal nevi caused by mosaic HRAS variants: one associating an extensive keratinocytic epidermal nevus with hypomastia, another with extensive mucosal involvement and a third combining a small sebaceous nevus with seizures and intellectual deficiency. Moreover, we performed extensive literature of all cases of syndromic epidermal nevi and related disorders with confirmed pathogenic postzygotic variants in HRAS, KRAS, NRAS or BRAF.

RESULTS

Most patients presented with bone, ophthalmological or neurological anomalies. Rhabdomyosarcoma, urothelial cell carcinoma and pubertas praecox are also repeatedly reported. KRAS pathogenic variants are involved in 50% of the cases, especially in sebaceous nevi, oculoectodermal syndrome and encephalocraniocutaneous lipomatosis. They are frequently associated with eye and brain anomalies. Pathogenic variants in HRAS are rather present in syndromic keratinocytic epidermal nevi and phacomatosis pigmentokeratotica.

CONCLUSION

This review delineates genotype/phenotype correlations of syndromic epidermal nevi with somatic RAS and BRAF pathogenic variants and may help improve their follow-up.

Encephalocraniocutaneous Lipomatosis: A Case Report

ABSTRACT

Encephalocraniocutaneous lipomatosis (ECCL) is a rare congenital syndrome and subclassification of oculoectodermal syndrome. Encephalocraniocutaneous lipomatosis may be associated with postzygotic mutations. However, absence of an identifiable mutation does not preclude a diagnosis of ECCL. Encephalocraniocutaneous lipomatosis commonly causes skin, eye, and central nervous system anomalies. Diagnosis can be made through genetic sequencing or standardized clinical criteria. One clinically apparent major criterion for the diagnosis of ECCL is nevus psiloliparus (NP), a fatty nevus with overlying nonscarring alopecia. In this case, a 50-day-old female infant with uncomplicated birth history presented to dermatology clinic for evaluation of 2 superficial cranial masses that had been present since birth without regression or evolution. One of the masses was located within the hairline and demonstrated overlying nonscarring alopecia, suspicious of NP. Because of concern for ECCL, brain magnetic resonance imaging was ordered and revealed 2 intracranial lipomas. Genetic testing was inconclusive. Excision of the masses was performed at the request of the parents for cosmetic purposes. Histologic evaluation of the surgical specimens confirmed the diagnosis of NP and ECCL. A suspected NP should raise concern for ECCL and prompt further evaluation for systemic involvement. In particular, patients with suspected ECCL should be screened for ocular and CNS involvement. Early identification and diagnosis are important for prognostication because patients with ECCL are at increased risk of developing neoplasms of the head and neck and may require more frequent screening examinations.

Next generation sequencing aids diagnosis and management in a case of encephalocraniocutaneous lipomatosis

Encephalocraniocutaneous lipomatosis (ECCL) is a rare neurocutaneous disorder caused by somatic FGFR1 and KRAS variants. It shares significant phenotypic overlap with several closely related disorders caused by mutations in the RAS-MAPK pathway (mosaic RASopathies). We report a diagnostically challenging case of ECCL in which next-generation sequencing of affected tissue identified a pathologic FGFR1 p.K656E variant, thereby establishing a molecular diagnosis. Patients with FGFR1-associated ECCL carry a risk of developing malignant brain tumors; thus, genetic testing of patients with suspected ECCL has important management implications.

Utility of Neonatal Findings in Early Diagnosis of a Case of Haberland Syndrome

Haberland syndrome or encephalocraniocutaneous lipomatosis (ECCL) is a rare, congenital syndrome characterized by lipomas and noncancerous tumors of the scalp, skin, and eyes, in addition to intellectual disability, early onset seizures, and ectomesodermal dysgenesis. The diagnosis of ECCL is classically made by clinical presentation, imaging, and histopathological findings, but due to the spectrum of clinical presentation and symptom severity, diagnosis is often delayed until adolescence or adulthood. Here we present a newborn male infant, one of the earliest case diagnoses to our knowledge, with a unique constellation of physical exam and neuroimaging findings consistent with this diagnosis. We aim to address important neonatal findings to aid in early detection and diagnosis of this unique disease, which is thought to improve clinical outcomes and patient quality of life.

Lymphatic disorders caused by mosaic, activating KRAS variants respond to MEK inhibition

Central conducting lymphatic anomaly (CCLA) due to congenital maldevelopment of the lymphatics can result in debilitating and life-threatening disease with limited treatment options. We identified 4 individuals with CCLA, lymphedema, and microcystic lymphatic malformation due to pathogenic, mosaic variants in KRAS. To determine the functional impact of these variants and identify a targeted therapy for these individuals, we used primary human dermal lymphatic endothelial cells (HDLECs) and zebrafish larvae to model the lymphatic dysplasia. Expression of the p.Gly12Asp and p.Gly13Asp variants in HDLECs in a 2‑dimensional (2D) model and 3D organoid model led to increased ERK phosphorylation, demonstrating these variants activate the RAS/MAPK pathway. Expression of activating KRAS variants in the venous and lymphatic endothelium in zebrafish resulted in lymphatic dysplasia and edema similar to the individuals in the study. Treatment with MEK inhibition significantly reduced the phenotypes in both the organoid and the zebrafish model systems. In conclusion, we present the molecular characterization of the observed lymphatic anomalies due to pathogenic, somatic, activating KRAS variants in humans. Our preclinical studies suggest that MEK inhibition should be studied in future clinical trials for CCLA due to activating KRAS pathogenic variants.

Clinical overview on RASopathies

RASopathies comprise a group of clinically overlapping developmental disorders caused by genetic variations affecting components or modulators of the RAS-MAPK signaling cascade, which lead to dysregulation of signal flow through this pathway. Noonan syndrome and the less frequent, clinically related disorders, Costello syndrome, cardiofaciocutaneous syndrome, Noonan syndrome with multiple lentigines, and Noonan syndrome-like disorder with loose anagen hair are part of the RASopathy spectrum and share a recognizable pattern of multisystem involvement. This review describes the "Noonan syndrome-like" phenotype as a common phenotypic signature of generalized developmental RAS pathway dysregulation. Distinctive features of the different entities are revisited against the background of the understanding of underlying genetic alterations and genotype correlations, which has evolved rapidly during the past 20 years, thereby leading to suggestions regarding the nosology of RASopathies.

Mosaic RASopathies: A review of disorders caused by somatic pathogenic variants in the genes of the RAS/MAPK pathway

Mosaic RASopathies are a heterogeneous group of diseases characterized by the presence at birth or early onset of congenital anomalies, cutaneous and vascular anomalies, segmental overgrowth, and increased cancer risk. They are caused by somatic pathogenic variants of the genes belonging the RAt Sarcoma Mitogen-activated protein kinase (RAS/MAPK) pathway causing its hyperactivation. Here, we review the clinical and molecular characteristics of this heterogeneous group of diseases, including the possibilities of molecular diagnosis and new therapeutic perspectives.

Fibrous dysplasia in cardio-facio-cutaneous syndrome: A case report and review of literature

Cardio-facio-cutaneous (CFC) syndrome (OMIM #:115150, 615278, 615279, 615280) is a rare genetic condition caused by variants in the RAS/mitogen-activated protein kinase (MAPK) signal transduction pathway. Up to 75% of cases are caused by mutations in the BRAF gene, whereas KRAS gene mutation has only been reported in <2% of cases. CFC syndrome is characterized by cardiac abnormalities, distinctive craniofacial dysmorphism, and various cutaneous abnormalities. Musculoskeletal and orthopedic manifestations are also prevalent in patients with CFC syndrome, among which the most common are skeletal deformities and joint laxities. Dysplastic bone disorders, on the other hand, have not been reported in CFC syndrome before. We report on a case of symmetrical polyostotic fibrous dysplasia (FD) in a patient with CFC syndrome with the KRAS(NM_004985.5):c.57G>C; p.Leu19Phe variant. The FDs were incidentally picked up, and patient was conservatively managed and remained asymptomatic on follow-up. The same variant was reported previously in a patient with Oculoectodermal Syndrome (OES), who developed polyostotic non-ossifying fibroma (NOF). This case explores FD as a possible new clinical feature of CFC syndrome, and when linked to the historical case of OES, explores whether the KRAS(NM_004985.5):c.57G>C; p.Leu19Phe mutation may potentially contribute to the development of dysplastic bone lesions in patients with this particular mutation.

A primary DICER1-sarcoma with KRAS and TP53 mutations in a child with suspected ECCL

A child had been followed since infancy by our multi-disciplinary neuro-oncology clinic with annual magnetic resonance imaging (MRI) under the presumed diagnosis of encephalocraniocutaneous lipomatosis (ECCL), with clinical features including nevus psiloliparus, scalp lipoma, nodular skin tag on and coloboma of the eyelid, cortical atrophy and meningeal angiomatosis. At the age of 4, she was found to have a large temporoparietal lesion causing elevated intracranial pressure requiring surgical resection. Histopathological exam of the tumor was suggestive of an intracranial sarcoma. Sequencing analysis of the tumor revealed mutations in DICER1, KRAS and TP53. Subsequent germline testing confirmed DICER1 syndrome and revealed an insignificant FGFR1 variant at a low frequency. Methylation profile of the tumor showed the tumor clustered most closely with sarcoma (rhabdomyosarcoma-like), confirming this tumor to be a primary DICER1-sarcoma. Compared to the previously reported cases, our unique case of primary DICER1-sarcoma also demonstrated neurofilament and chromogranin positivity, and genomic instability with loss of chromosome 4p, 4q, 8p, 11p, and 19p, as well as gains in chromosome 7p, 9p, 9q, 13q, and 15q on copy variant analysis. The detailed sequencing and methylation information discovered in this unique case of DICER1-sarcoma will hopefully help further our understanding of this rare and emerging entity.

Toward clinical and molecular dissection of frontonasal dysplasia with facial skin polyps: From Pai syndrome to differential diagnosis through a series of 27 patients

Unique or multiple congenital facial skin polyps are features of several rare syndromes, from the most well-known Pai syndrome (PS), to the less recognized oculoauriculofrontonasal syndrome (OAFNS), encephalocraniocutaneous lipomatosis (ECCL), or Sakoda complex (SC). We set up a research project aiming to identify the molecular bases of PS. We reviewed 27 individuals presenting with a syndromic frontonasal polyp and initially referred for PS. Based on strict clinical classification criteria, we could confirm only nine (33%) typical and two (7%) atypical PS individuals. The remaining ones were either OAFNS (11/27-41%) or presenting with an overlapping syndrome (5/27-19%). Because of the phenotypic overlap between these entities, OAFNS, ECCL, and SC can be either considered as differential diagnosis of PS or part of the same spectrum. Exome and/or genome sequencing from blood DNA in 12 patients and from affected tissue in one patient failed to identify any replication in candidate genes. Taken together, our data suggest that conventional approaches routinely utilized for the identification of molecular etiologies responsible for Mendelian disorders are inconclusive. Future studies on affected tissues and multiomics studies will thus be required in order to address either the contribution of mosaic or noncoding variation in these diseases.

Identification of Codon 146 KRAS Variants in Isolated Epidermal Nevus and Multiple Lesions in Oculoectodermal Syndrome: Confirmation of the Phenotypic Continuum of Mosaic RASopathies

Mosaic RASopathies are a molecularly heterogeneous group of (neuro)cutaneous syndromes with high phenotypical variability. Postzygotic variants in KRAS have been described in oculoectodermal syndrome (OES), encephalocraniocutaneous lipomatosis (ECCL) and epidermal nevus syndrome (ENS). This study confirms the continuum of mosaic neurocutaneous RASopathies showing codon 146 KRAS variants in an individual with OES and, for the first time, in an individual with (isolated) epidermal nevus. The presence of a nevus psiloliparus in individuals with OES indicates that this finding is not specific for ECCL and highlights the phenotypical overlap between ECCL and OES. The presence of the somatic KRAS variant in the nevus psiloliparus resolves the underlying molecular etiology of this fatty-tissue nevus. In addition, this finding refutes the theory of non-allelic twin-spotting as an underlying hypothesis to explain the concurrent presence of two different mosaicisms in one individual. The identification of codon 146 KRAS variants in isolated epidermal nevus introduces a new hot spot for this condition, which is useful for increasing molecular genetic testing using targeted gene sequencing panels.

Classification of KRAS-Activating Mutations and the Implications for Therapeutic Intervention

Members of the family of RAS proto-oncogenes, discovered just over 40 years ago, were among the first cancer-initiating genes to be discovered. Of the three RAS family members, KRAS is the most frequently mutated in human cancers. Despite intensive biological and biochemical study of RAS proteins over the past four decades, we are only now starting to devise therapeutic strategies to target their oncogenic properties. Here, we highlight the distinct biochemical properties of common and rare KRAS alleles, enabling their classification into functional subtypes. We also discuss the implications of this functional classification for potential therapeutic avenues targeting mutant subtypes.

SIGNIFICANCE

Efforts in the recent past to inhibit KRAS oncogenicity have focused on kinases that function in downstream signal transduction cascades, although preclinical successes have not translated to patients with KRAS-mutant cancer. Recently, clinically effective covalent inhibitors of KRASG12C have been developed, establishing two principles that form a foundation for future efforts. First, KRAS is druggable. Second, each mutant form of KRAS is likely to have properties that make it uniquely druggable.

Expending the Phenotypic Spectrum of Encephalocraniocutaneous Lipomatosis: About a Prenatal Case With Complete Autopsy

Encephalocraniocutaneous lipomatosis (ECCL) or Haberland syndrome (MIM #613001) is a rare congenital neurocutaneous disorder. It is characterized by unilateral ocular, cutaneous and central nervous system anomalies. Key clinical features include hairless fatty tissue nevus of the scalp, choristoma of the eye and intraspinal and intracerebral lipomas. We report one of the first cases diagnosed after termination of pregnancy at 35 WG, including antenatal and post-mortem imaging, complete autopsy and genetic analysis. Prenatal ultrasound and MRI of the third trimester showed multifocal spinal lesions and left lateral cerebral ventriculomegaly with cerebral atrophy. Diagnosis of ECCL was suggested at complete autopsy which revealed nevus psiloliparus of the scalp, facial hamartomas and intracranial and spinal lipomas. In addition, our case also exhibited a cardiac rhabdomyoma and a multicystic dysplastic kidney, both never reported to date in this syndrome. ECCL was confirmed by the identification of a postzygotic FGFR1 mutation. We reviewed the literature and discuss the pathogenesis of this syndrome.

Choroidal calcifications in two cases of aplasia cutis congenita and oculoectodermal syndrome

PURPOSE

To describe choroidal calcifications as an ophthalmic feature in aplasia cutis congenita (ACC) with oculoectodermal syndrome (OES).

OBSERVATIONS

Two cases of ACC/OES with characteristic echographic evidence of choroidal calcifications are described.

CONCLUSIONS AND IMPORTANCE

The ophthalmic manifestations of ACC/OES may be expanded to include choroidal calcifications. The presence of a choroidal calcification with B-scan ultrasound in a case suspicious for ACC/OES may facilitate a more timely diagnosis and inform future follow-up regimens to monitor ophthalmic and systemic manifestations of this disease.

Lateralized and Segmental Overgrowth in Children

Congenital disorders of lateralized or segmental overgrowth (LO) are heterogeneous conditions with increased tissue growth in a body region. LO can affect every region, be localized or extensive, involve one or several embryonic tissues, showing variable severity, from mild forms with minor body asymmetry to severe ones with progressive tissue growth and related relevant complications. Recently, next-generation sequencing approaches have increased the knowledge on the molecular defects in LO, allowing classifying them based on the deranged cellular signaling pathway. LO is caused by either genetic or epigenetic somatic anomalies affecting cell proliferation. Most LOs are classifiable in the Beckwith-Wiedemann spectrum (BWSp), PI3KCA/AKT-related overgrowth spectrum (PROS/AROS), mosaic RASopathies, PTEN Hamartoma Tumor Syndrome, mosaic activating variants in angiogenesis pathways, and isolated LO (ILO). These disorders overlap over common phenotypes, making their appraisal and distinction challenging. The latter is crucial, as specific management strategies are key: some LO is associated with increased cancer risk making imperative tumor screening since childhood. Interestingly, some LO shares molecular mechanisms with cancer: recent advances in tumor biological pathway druggability and growth downregulation offer new avenues for the treatment of the most severe and complicated LO.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

Somatic KRAS mutation affecting codon 146 in linear sebaceous nevus syndrome

Linear Sebaceous Nevus Syndrome is a rare disorder that presents with nevus sebaceus in association with corneal dermoids, colobomas, choroidal osteomas, and arachnoid cysts. It is thought to represent a mosaic RASopathy. These are disorders characterized by postzygotic somatic mutation in genes involved in RAS/MAPK signaling pathway. In this report we describe two patients with linear sebaceous nevus syndrome found to have mutations in codon 146 of KRAS with evidence of mosaicism. This specific mutation has previously been reported in Oculoectodermal Syndrome and Encephalocraniocutaneous Lipomatosis, two other mosaic RASopathies with predominantly cerebrooculocutaneous manifestations. These findings suggest that, while initially classified as different syndromes, these disorders should be evaluated and managed as a spectrum of related disorders.

Novel findings and expansion of phenotype in a mosaic RASopathy caused by somatic KRAS variants

Mosaic KRAS variants and other RASopathy genes cause oculoectodermal, encephalo-cranio-cutaneous lipomatosis, and Schimmelpenning-Feuerstein-Mims syndromes, and a spectrum of vascular malformations, overgrowth and other associated anomalies, the latter of which are only recently being characterized. We describe eight individuals in total (six unreported cases and two previously reported cases) with somatic KRAS variants and variably associated features. Given the findings of somatic overgrowth (in seven individuals) and vascular or lymphatic malformations (in eight individuals), we suggest mosaic RASopathies (mosaic KRAS variants) be considered in the differential diagnosis for individuals presenting with asymmetric overgrowth and lymphatic or vascular anomalies. We expand the association with embryonal tumors, including the third report of embryonal rhabdomyosarcoma, as well as novel findings of Wilms tumor and nephroblastomatosis in two individuals. Rare or novel findings in our series include the presence of epilepsy, polycystic kidneys, and T-cell deficiency in one individual, and multifocal lytic bone lesions in two individuals. Finally, we describe the first use of targeted therapy with a MEK inhibitor for an individual with a mosaic KRAS variant. The purposes of this report are to expand the phenotypic spectrum of mosaic KRAS-related disorders, and to propose possible mechanisms of pathogenesis, and surveillance of its associated findings.

Pathogenic postzygotic mosaicism in the tyrosine receptor kinase pathway: potential unidentified human disease hidden away in a few cells

Mutations occurring during embryonic development affect only a subset of cells resulting in two or more distinct cell populations that are present at different levels, also known as postzygotic mosaicism (PZM). Although PZM is a common biological phenomenon, it is often overlooked as a source of disease due to the challenges associated with its detection and characterization, especially for very low-frequency variants. Moreover, PZM can cause a different phenotype compared to constitutional mutations. Especially, lethal mutations in receptor tyrosine kinase (RTK) pathway genes, which exist only in a mosaic state, can have completely new clinical manifestations and can look very different from the associated monogenic disorder. However, some key questions are still not addressed, such as the level of mosaicism resulting in a pathogenic phenotype and how the clinical outcome changes with the development and age. Addressing these questions is not trivial as we require methods with the sensitivity to capture some of these variants hidden away in very few cells. Recent ultra-accurate deep-sequencing approaches can now identify these low-level mosaics and will be central to understand systemic and local effects of mosaicism in the RTK pathway. The main focus of this review is to highlight the importance of low-level mosaics and the need to include their detection in studies of genomic variation associated with disease.

Ocular manifestations of ectodermal dysplasia

Purpose

The ectodermal dysplasias (EDs) constitute a group of disorders characterized by abnormalities in two or more ectodermal derivatives, including skin, hair, teeth, and sweat glands. The purpose of the current study was to evaluate ocular manifestations in pediatric patients with ED.

Methods

Retrospective case series including consecutive ED subjects who were treated in the ophthalmology department at the Children’s Hospital of Philadelphia over a 12-year period (2009–2020). Main Outcome Measures were ocular and ocular adnexal abnormalities.

Results

Thirty subjects were included: 20 males (67%), mean age of 4.5 years (range 0.3–18). Patients with different subtypes were included, with the hypohidrotic ED and ectrodactyly-ectodermal dysplasia-clefting variants being most prevalent. Most common findings were: lacrimal drainage obstruction in 12 (40%) including punctal agenesis in 10 (33%), refractive errors in 13 (43%) and amblyopia in 6 (20%). A new finding of eyelid ptosis or eyelash ptosis was demonstrated in 11 subjects (37%), mostly associated with TP63 or EDA1 genes variants.

Conclusion

Ectodermal dysplasias are associated with various ocular pathologies and amblyopia in the pediatric population. We report a possible genetic association between lash ptosis and EDA1 gene, and eyelid ptosis and TP63 or EDA1 genes variants.

Neuroimaging manifestations of epidermal nevus syndrome

Epidermal nevus syndrome (ENS) represents a diverse group of rare neurocutaneous diseases associated with the presence of characteristic epidermal nevi (EN) in the skin and extracutaneous manifestations in the eyes, skeletal, urogenital and central nervous systems. We present a case series of 7 children with ENS, with specific attention to the neuroradiological characteristics of this entity.

Disorders Caused by Genetic Mosaicism

BACKGROUND

Genetic mosaics arise through new mutations occurring after fertiliza- tion (i.e., postzygotic mutations). Mosaics have been described in recent years as the cause of many different disorders; many of these are neurocutaneous diseases and syndromal developmental disorders, each with a characteristic phenotype. In some of these disorders, there is a genetic predisposition to the development of tumors. This article is intended as an overview of selected mosaic diseases.

METHODS

This review is based on publications retrieved by a selective search in PubMed, with particular attention to recent articles in high-ranking journals dealing with asymmetric growth disturbances, focal brain malformations, mosaic diseases due to dysregulation of the RAS/RAF signaling pathway (mosaic RASopathies), and vascular malformations.

RESULTS

The identification of postzygotic mutations has led to the reclassification of traditional disease entities and to a better understanding of their pathogenesis. Diagnosis is aided by modern next-generation sequencing (NGS) techniques that allow the detection even of low-grade mosaics. Many mosaic mutations are not detectable in blood, but only in the affected tissue, e.g., the skin. Genetic mosaic diseases often manifest themselves in the skin and brain, and by facial dysmorphism, asymmetrical growth disturbances, and vascular malformations.

CONCLUSION

The possibility of a mosaic disease should be kept in mind in the diag- nostic evaluation of patients with asymmetrical growth disturbances, focal neuronal migration disturbances, vascular malformations, and linear skin abnormalities. The demonstration of a postzygotic mutation often affords relief to the parents of an affected child, since this means that there is no increased risk for recurrence of the same disorder in future children. Correct classification is important, as molecular available for certain mosaic diseases, e.g., PIK3CA-related overgrowth spectrum (PROS) disorder.

An update on oculocerebrocutaneous (Delleman-Oorthuys) syndrome

Oculocerebrocutaneous syndrome (OCCS) is a rare disorder characterized primarily by congenital skin, eye, and brain anomalies. The most distinctive findings are hypoplastic or aplastic skin defects; pedunculated, typically hamartomatous, or nodular skin appendages; cystic microphthalmia; and a combination of forebrain anomalies and a specific mid-hindbrain malformation. Based on a review of 40 patients with OCCS, existing clinical criteria have been revised. Because of the asymmetric and patchy distribution of features, lack of recurrence in families, male preponderance and completely skewed X-inactivation in one female, OCCS is hypothesized to result from postzygotic mosaic variants in an X-linked gene. Whole exome and genome sequencing on blood DNA in two patients failed to identify pathogenic variants so far. In view of the overlapping features, in particular of the brain, of OCCS and Aicardi syndrome, both may be pathogenetically related or even result from different variants in the same gene. For the elucidation of the cause of OCCS, exome or genome sequencing on multiple lesional tissues is the primary goal.

FGFR1 Mosaic Pathogenic Variant in Encephalocraniocutaneous Lipomatosis with Leptomeningeal Angiomatosis

Encephalocraniocutaneous lipomatosis (ECCL) is a congenital neurocutaneous disorder. It is characterized by ocular anomalies (epibulbar choristomas), skin lesions (as nevus psiloliparus and subcutaneous lipomas), and central nervous system abnormalities (mostly arachnoid cysts, brain anomalies, vascular defects, and intracranial and spinal lipomas). Mutations in KRAS and fibroblast growth factor receptor gene-1 (FGFR1) are related to ECCL, explaining additional manifestations such as jaw tumors or gliomas. We report a pediatric patient with clinical, radiological, and histological findings consistent with ECCL and a mosaic pathogenic variant in FGFR1 found in the DNA from a non-cultured biopsy of the nevus psiloliparus and absent in blood and DNA from buccal mucosa.

Sensitive detection of FGFR1 N546K mosaic mutation in patient with encephalocraniocutaneous lipomatosis and pilocytic astrocytoma

Encephalocraniocutaneous lipomatosis (ECCL) is a rare neurocutaneous disorder, with only about 100 cases reported worldwide. It is characterized by congenital lesions of the eye, skin, and central nervous system. Only recently, potential causative FGFR1 point mutations have been identified in brain tumors and cultured skin biopsies from patients with this condition. Here, we analyzed the molecular status of a patient with ECCL and a coexisting pilocytic astrocytoma with detected FGFR1 N546K mutation. The presence of the alteration in both affected and unaffected tissues has been evaluated using Sanger sequencing and droplet digital polymerase chain reaction (ddPCR) technique. The ddPCR analysis showed differential distribution of the alteration in all specimens, including unaffected and untreated samples. Therefore, we confirm that FGFR1 N546K is a plausible causative mutation of ECCL patients and could be associated with a risk of brain tumor development. We also show the usefulness of sensitive ddPCR method for detection of low levels of autosomal mosaic mutation in blood or swabs. We suggest that utilization of this method may improve the diagnostic process, especially when targeted therapies are considered.

Expansion of the phenotypic spectrum and description of molecular findings in a cohort of patients with oculocutaneous mosaic RASopathies

BACKGROUND

Postzygotic KRAS, HRAS, NRAS, and FGFR1 mutations result in a group of mosaic RASopathies characterized by related developmental anomalies in eye, skin, heart, and brain. These oculocutaneous disorders include oculoectodermal syndrome (OES) encephalo-cranio-cutaneous lipomatosis (ECCL), and Schimmelpenning-Feuerstein-Mims syndrome (SFMS). Here, we report the results of the clinical and molecular characterization of a novel cohort of patients with oculocutaneous mosaic RASopathies.

METHODS

Two OES, two ECCL, and two SFMS patients were ascertained in the study. In addition, two subjects with unilateral isolated epibulbar dermoids were also enrolled. Molecular analysis included PCR amplification and Sanger sequencing of KRAS, HRAS, NRAS, and FGFR1 genes in DNA obtained from biopsies (skin/epibulbar dermoids), buccal mucosa, and blood leukocytes. Massive parallel sequencing was employed in two cases with low-level mosaicism.

RESULTS

In DNA from biopsies, mosaicism for pathogenic variants, including KRAS p.Ala146Thr in two OES subjects, FGFR1 p.Asn546Lys and KRAS p.Ala146Val in ECCL patients, and KRAS p.Gly12Asp in both SFMS patients, was demonstrated. No mutations were shown in DNA from conjunctival lesions in two subjects with isolated epibubar dermoids.

CONCLUSION

Our study allowed the expansion of the clinical spectrum of mosaic RASopathies and supports that mosaicism for recurrent mutations in KRAS and FGFR1 is a commonly involved mechanism in these rare oculocutaneous anomalies.

Posterior quadrantic dysplasia with localized hemimegalencephaly in a patient with giant congenital melanocytic nevus: First case report

Giant congenital melanocytic nevus (GCMN) is associated with neurocutaneous melanocytosis and various other neurological complications. Its association with migrational anomalies of the brain is extremely rare. Herein, we document the first case of GCMN in a one-day-old baby associated with localized hemimegalencephaly (HME) of the brain with extensive malformation of cortical development including polymicrogyria, pachygyria and sublobar dysplasia, limited to an enlarged quadrant of the brain. HME and GCMN are considered embryological anomalies of cell migration and proliferation. We discuss the unusual magnetic resonance imaging findings along with a brief review of the literature. To the best of our knowledge, our case is the first to report the association of GCMN with localized HME.

The oculoauriculofrontonasal syndrome: Further clinical characterization and additional evidence suggesting a nontraditional mode of inheritance

The oculoauriculofrontonasal syndrome (OAFNS) is a rare disorder characterized by the association of frontonasal dysplasia (widely spaced eyes, facial cleft, and nose abnormalities) and oculo-auriculo-vertebral spectrum (OAVS)-associated features, such as preauricular ear tags, ear dysplasia, mandibular asymmetry, epibulbar dermoids, eyelid coloboma, and costovertebral anomalies. The etiology is unknown so far. This work aimed to identify molecular bases for the OAFNS. Among a cohort of 130 patients with frontonasal dysplasia, accurate phenotyping identified 18 individuals with OAFNS. We describe their clinical spectrum, including the report of new features (micro/anophtalmia, cataract, thyroid agenesis, polymicrogyria, olfactory bulb hypoplasia, and mandibular cleft), and emphasize the high frequency of nasal polyps in OAFNS (56%). We report the negative results of ALX1, ALX3, and ALX4 genes sequencing and next-generation sequencing strategy performed on blood-derived DNA from respectively, four and four individuals. Exome sequencing was performed in four individuals, genome sequencing in one patient with negative exome sequencing result. Based on the data from this series and the literature, diverse hypotheses can be raised regarding the etiology of OAFNS: mosaic mutation, epigenetic anomaly, oligogenism, or nongenetic cause. In conclusion, this series represents further clinical delineation work of the rare OAFNS, and paves the way toward the identification of the causing mechanism.

The Rare Neurocutaneous Disorders: Update on Clinical, Molecular, and Neuroimaging Features

Phakomatoses, also known as neurocutaneous disorders, comprise a vast number of entities that predominantly affect structures originated from the ectoderm such as the central nervous system and the skin, but also the mesoderm, particularly the vascular system. Extensive literature exists about the most common phakomatoses, namely neurofibromatosis, tuberous sclerosis, von Hippel-Lindau and Sturge-Weber syndrome. However, recent developments in the understanding of the molecular underpinnings of less common phakomatoses have sparked interest in these disorders. In this article, we review the clinical features, current pathogenesis, and modern neuroimaging findings of melanophakomatoses, vascular phakomatoses, and other rare neurocutaneous syndromes that may also include tissue overgrowth or neoplastic predisposition.

Mosaic RAS/MAPK variants cause sporadic vascular malformations which respond to targeted therapy

BACKGROUND. Sporadic vascular malformations (VMs) are complex congenital anomalies of blood vessels that lead to stroke, life-threatening bleeds, disfigurement, overgrowth, and/or pain. Therapeutic options are severely limited, and multidisciplinary management remains challenging, particularly for high-flow arteriovenous malformations (AVM).

METHODS. To investigate the pathogenesis of sporadic intracranial and extracranial VMs in 160 children in which known genetic causes had been excluded, we sequenced DNA from affected tissue and optimized analysis for detection of low mutant allele frequency.

RESULTS. We discovered multiple mosaic-activating variants in 4 genes of the RAS/MAPK pathway, KRAS, NRAS, BRAF, and MAP2K1, a pathway commonly activated in cancer and responsible for the germline RAS-opathies. These variants were more frequent in high-flow than low-flow VMs. In vitro characterization and 2 transgenic zebrafish AVM models that recapitulated the human phenotype validated the pathogenesis of the mutant alleles. Importantly, treatment of AVM-BRAF mutant zebrafish with the BRAF inhibitor vemurafinib restored blood flow in AVM.

CONCLUSION. Our findings uncover a major cause of sporadic VMs of different clinical types and thereby offer the potential of personalized medical treatment by repurposing existing licensed cancer therapies.

FUNDING. This work was funded or supported by grants from the AVM Butterfly Charity, the Wellcome Trust (UK), the Medical Research Council (UK), the UK National Institute for Health Research, the L’Oreal-Melanoma Research Alliance, the European Research Council, and the National Human Genome Research Institute (US).

Nonepithelial Tumors and Tumor-like Lesions of the Skin and Subcutis in Children

This overview of mesenchymal tumors presenting in the skin and/or subcutis in children brings together the range of neoplasms and hamartomas which are seen in this age-group. It is not surprising from the perspective of the pediatric or general surgical pathologist that vascular anomalies, including true neoplasms and vascular malformations, are the common phenotypic category. Since there is considerable morphologic overlap among these lesions, clinicopathologic correlation may be more important than for many of the other mesenchymal tumors. The skin and subcutis are the most common sites of clinical presentation for the infantile myofibroma which is the most common of fibrous mesenchymal tumors in children. Several of the other mesenchymal tumors are more common adults-like dermatofibrosarcoma protuberans, but nonetheless have an important presence in children, even as a congenital neoplasm. A lipomatous tumor in a young child should be considered as a possible manifestation of an overgrowth syndrome.

Down syndrome, RASopathies, and other rare syndromes

In this article we discuss the occurrence of myeloid neoplasms in patients with a range of syndromes that are due to germline defects of the RAS signaling pathway and in patients with trisomy 21. Both RAS mutations and trisomy 21 are common somatic events contributing to leukemogenis. Thus, the increased leukemia risk observed in children affected by these conditions is biologically highly plausible. Children with myeloid neoplasms in the context of these syndromes require different treatments than children with sporadic myeloid neoplasms and provide an opportunity to study the role of trisomy 21 and RAS signaling during leukemogenesis and development.

Rationale for RAS mutation-tailored therapies

RAS mutations are among the most common genetic alterations found in cancerous tumors but rational criteria or strategies for targeting RAS-dependent tumors are only recently emerging. Clinical and laboratory data suggest that patient selection based on specific RAS mutations will be an essential component of these strategies. A thorough understanding of the biochemical and structural properties of mutant RAS proteins form the theoretical basis for these approaches. Direct inhibition of KRAS G12C by covalent inhibitors is a notable recent example of the RAS mutation-tailored approach that establishes a paradigm for other RAS mutation-centered strategies.