GNAQ/GNA11 Mosaicism Causes Aberrant Calcium Signaling Susceptible to Targeted Therapeutics

Mosaic variants in genes GNAQ or GNA11 lead to a spectrum of vascular and pigmentary diseases including Sturge-Weber syndrome, in which progressive postnatal neurological deterioration led us to seek biologically targeted therapeutics. Using two cellular models, we find that disease-causing GNAQ/11 variants hyperactivate constitutive and G-protein coupled receptor ligand-induced intracellular calcium signaling in endothelial cells. We go on to show that the aberrant ligand-activated intracellular calcium signal is fueled by extracellular calcium influx through calcium-release-activated channels. Treatment with targeted small interfering RNAs designed to silence the variant allele preferentially corrects both the constitutive and ligand-activated calcium signaling, whereas treatment with a calcium-release-activated channel inhibitor rescues the ligand-activated signal. This work identifies hyperactivated calcium signaling as the primary biological abnormality in GNAQ/11 mosaicism and paves the way for clinical trials with genetic or small molecule therapies.

GNAQ/GNA11 Mosaicism Is Associated with Abnormal Serum Calcium Indices and Microvascular Neurocalcification

Mosaic mutations in genes GNAQ or GNA11 lead to a spectrum of diseases including Sturge-Weber syndrome and phakomatosis pigmentovascularis with dermal melanocytosis. The pathognomonic finding of localized "tramlining" on plain skull radiography, representing medium-sized neurovascular calcification and associated with postnatal neurological deterioration, led us to study calcium metabolism in a cohort of 42 children. In this study, we find that 74% of patients had at least one abnormal measurement of calcium metabolism, the commonest being moderately low serum ionized calcium (41%) or high parathyroid hormone (17%). Lower levels of ionized calcium even within the normal range were significantly associated with seizures, and with specific antiepileptics despite normal vitamin D levels. Successive measurements documented substantial intrapersonal fluctuation in indices over time, and DEXA scans were normal in patients with hypocalcemia. Neurohistology from epilepsy surgery in five patients revealed not only intravascular, but perivascular and intraparenchymal mineral deposition and intraparenchymal microvascular disease in addition to previously reported findings. Neuroradiology review clearly demonstrated progressive calcium deposition in individuals over time. These findings and those of the adjoining paper suggest that calcium deposition in the brain of patients with GNAQ/GNA11 mosaicism may not be a nonspecific sign of damage as was previously thought, but may instead reflect the central postnatal pathological process in this disease spectrum.

Mosaic BRAF Fusions Are a Recurrent Cause of Congenital Melanocytic Nevi Targetable by MAPK Pathway Inhibition

Among children with multiple congenital melanocytic nevi, 25% have no established genetic cause, of whom many develop a hyperproliferative and severely pruritic phenotype resistant to treatment. Gene fusions have been reported in individual cases of congenital melanocytic nevi. We studied 169 patients with congenital melanocytic nevi in this study, 38 of whom were double wild type for pathogenic NRAS/BRAF variants. Nineteen of these 38 patients had sufficient tissue to undergo RNA sequencing, which revealed mosaic BRAF fusions in 11 of 19 patients and mosaic RAF1 fusions in 1 of 19. Recurrently, fusions involved the loss of the 5´ regulatory domain of BRAF or RAF1 but preserved the kinase domain. We validated all cases and detected the fusions in two separate nevi in 5 of 12 patients, confirming clonality. The absence of the fusion in blood in 8 of 12 patients indicated mosaicism. Primary culture of BRAF-fusion nevus cells from 3 of 12 patients demonstrated highly increased MAPK activation, despite only mildly increased BRAF expression, suggesting additional mechanisms of kinase activation. Trametinib quenched MAPK hyperactivation in vitro, and treatment of two patients caused rapid improvement in bulk tissue, improving bodily movement and reducing inflammation and severe pruritus. These findings offer a genetic diagnosis to an additional group of patients and trametinib as a treatment option for the severe associated phenotypes.

Vitamin D status in children with congenital melanocytic nevi

Congenital melanocytic nevi (CMN) are rare, pigmented birthmarks that can predispose patients to melanoma of the central nervous system and skin. Data from non-CMN melanoma cohorts suggest that vitamin D levels may be connected to outcome, prompting this study of 25-hydroxyvitamin D levels in plasma samples from 40 children with CMN. While 27% were insufficient and 13% deficient, this was representative of European populations, and UK supplementation guidelines are already in place. Our data support routine vitamin D supplementation for all CMN patients during winter months, without routine serum measurement.

PTPN11 Mosaicism Causes a Spectrum of Pigmentary and Vascular Neurocutaneous Disorders and Predisposes to Melanoma

Phakomatosis pigmentovascularis is a diagnosis that denotes the coexistence of pigmentary and vascular birthmarks of specific types, accompanied by variable multisystem involvement, including CNS disease, asymmetrical growth, and a predisposition to malignancy. Using a tight phenotypic group and high-depth next-generation sequencing of affected tissues, we discover here clonal mosaic variants in gene PTPN11 encoding SHP2 phosphatase as a cause of phakomatosis pigmentovascularis type III or spilorosea. Within an individual, the same variant is found in distinct pigmentary and vascular birthmarks and is undetectable in blood. We go on to show that the same variants can cause either the pigmentary or vascular phenotypes alone, and drive melanoma development within pigmentary lesions. Protein structure modeling highlights that although variants lead to loss of function at the level of the phosphatase domain, resultant conformational changes promote longer ligand binding. In vitro modeling of the missense variants confirms downstream MAPK pathway overactivation and widespread disruption of human endothelial cell angiogenesis. Importantly, patients with PTPN11 mosaicism theoretically risk passing on the variant to their children as the germline RASopathy Noonan syndrome with lentigines. These findings improve our understanding of the pathogenesis and biology of nevus spilus and capillary malformation syndromes, paving the way for better clinical management.

Impact of public exhibition on the perception of birthmarks

BACKGROUND

The importance of photographs in social media, the steep rise in popularity of tattoos, and the prominence of individuals with visibly different skin in fashion are likely to be changing the landscape of self- and public perception of birthmarks. Study objectives were to assess the impact of a photoshoot and public exhibition on the self-perception of individuals with extensive birthmarks, and to explore the viewing public's reactions.

METHODS

Thirty individuals with congenital melanocytic nevi (CMN) were recruited internationally. Each had a professional photoshoot portrait with their skin exposed, resulting in a public exhibition in London entitled "How do you C Me Now?" Participants/parents completed pre- and post-questionnaires relating to self-perception and the impact of their birthmarks on behavior. Over 8000 members of the public viewed the exhibition, 464 completing an on-site questionnaire on its effects.

RESULTS

All participants/parents rated the experience as positive, valuable and helpful. Scores on self-appreciation and self-confidence were significantly higher after the photo shoot. Members of the general public overwhelmingly reported the exhibition increased their positive feelings towards people with birthmarks. The majority of public respondents also reported that the exhibition made them feel better about their own skin and about their looks in general.

CONCLUSION

This unique exhibition and the associated research has provided a striking new perspective on potential psychological interventions for individuals with birthmarks.

Mosaic PRKACA duplication causing a novel and distinct phenotype of early-onset Cushing's syndrome and acral cutaneous mucinosis

SIGNIFICANCE STATEMENT

We describe a mosaic PRKACA duplication in a young infant who presented with a Carney-like complex: bilateral non-pigmented micronodular adrenal hyperplasia, severe early-onset Cushing's syndrome, and distinct acral soft tissue overgrowth due to cutaneous mucinosis. This represents a novel manifestation of PRKACA disruption and broadens the extra-adrenal phenotype of PRKACA-associated Cushing's syndrome. Our data suggest that Cushing's syndrome phenotypes arising from somatic and germline PRKACA abnormalities can exist on a spectrum. We emphasise the value of ascertaining a genetic diagnosis for PRKACA-mediated adrenal and extra-adrenal disease to guide individualised and targeted care.

Abstract 851: Functional dissection of GNAQ and GNA11 oncogenic mutations identifies potential targeted therapy

Background: Oncogenic variants of GNAQ and GNA11 arising in embryonic or fetal development lead to a spectrum of congenital mosaic disorders including Sturge-Weber syndrome (SWS) and Phakomatosis Pigmentovascularis (PPV). Both SWS and PPV are characterised by vascular malformations in brain, skin and eye, with worsening neurological sequelae after birth suggesting a potential treatment window. Although the genetic causes are understood, and previous data in non-disease-specific cell lines have suggested MAPK activation, the functional effects of the mutations in vascular endothelium have not been studied. The characteristic finding of intracerebral intravascular calcification led us to hypothesise that intra-cellular calcium-signalling disturbances leading to localised imbalances in calcium homeostasis may be involved in disease pathogenesis.

Methods: Stable cell lines were established to study cell signalling downstream of GNAQ c.548G>A, p.(R183Q) or GNA11 c.547C>T, p.(R183C) variants in endothelial cells. We re-expressed mutant GNAQ or GNA11 alleles in HEK293 cells in which both endogenous genes had been knocked out for validation purposes. Constitutive calcium signaling was evaluated by measuring inositol-monophosphate accumulation and by a NFAT-luciferase reporter assay, while ligand-stimulated calcium signaling was monitored over time following incubation with intra-cellular calcium probe Fluo-8. In a parallel complementary study, serum calcium and related indices were assayed in 35 patients with SWS or PPV, consented for research under appropriate approvals.

Results: GNAQ and GNA11 variants led to marked constitutive calcium signalling in vascular endothelial cells, but not to MAPK activation. GNAQ-mutant endothelial cells also showed aberrant calcium signalling responses to GPCR ligand, which led in turn to sustained replenishment of intracellular calcium stores from the extracellular space. These calcium signalling defects could be rescued by a specific calcium channel inhibitor. Strikingly, and previously undescribed in these diseases, 43% of patients were found to have hypocalcaemia, and 20% hyperparathyroidism, currently presumed secondary but under further investigation.

Conclusions: GNAQ mosaicism leads to constitutive and ligand-induced over-activation of intracellular calcium signalling, which increases influx of calcium from the extracellular to the intracellular space and could be the explanation for systemic hypocalcaemia in a substantial proportion of patients. These data have immediate implications for clinical management of these mosaic diseases, and shed light on the in vivo pathogenic actions of of GNAQ/GNA11 oncogenic variants.

Citation Format: Davide Zecchin, Nicole Knoepfel, Anna Gluck, Mark Stevenson, Kate E. Lines, Satyamaanasa Polubothu, Noreen Muwanga-Nanyonjo, Sara Barberan-Martin, Fanourios Michailidis, Dale Bryant, Ulrike Loebel, Asuka Inoue, Robert Semple, Sarah Aylett, Rajesh V. Thakker, Veronica A. Kinsler. Functional dissection of GNAQ and GNA11 oncogenic mutations identifies potential targeted therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 851.

Inherited duplications of PPP2R3B predispose to nevi and melanoma via a C21orf91-driven proliferative phenotype

PURPOSE

Much of the heredity of melanoma remains unexplained. We sought predisposing germline copy-number variants using a rare disease approach.

METHODS

Whole-genome copy-number findings in patients with melanoma predisposition syndrome congenital melanocytic nevus were extrapolated to a sporadic melanoma cohort. Functional effects of duplications in PPP2R3B were investigated using immunohistochemistry, transcriptomics, and stable inducible cellular models, themselves characterized using RNAseq, quantitative real-time polymerase chain reaction (qRT-PCR), reverse phase protein arrays, immunoblotting, RNA interference, immunocytochemistry, proliferation, and migration assays.

RESULTS

We identify here a previously unreported genetic susceptibility to melanoma and melanocytic nevi, familial duplications of gene PPP2R3B. This encodes PR70, a regulatory unit of critical phosphatase PP2A. Duplications increase expression of PR70 in human nevus, and increased expression in melanoma tissue correlates with survival via a nonimmunological mechanism. PPP2R3B overexpression induces pigment cell switching toward proliferation and away from migration. Importantly, this is independent of the known microphthalmia-associated transcription factor (MITF)-controlled switch, instead driven by C21orf91. Finally, C21orf91 is demonstrated to be downstream of MITF as well as PR70.

CONCLUSION

This work confirms the power of a rare disease approach, identifying a previously unreported copy-number change predisposing to melanocytic neoplasia, and discovers C21orf91 as a potentially targetable hub in the control of phenotype switching.

Somatic mutations of GNA11 and GNAQ in CTNNB1-mutant aldosterone-producing adenomas presenting in puberty, pregnancy or menopause

Most aldosterone-producing adenomas (APAs) have gain-of-function somatic mutations of ion channels or transporters. However, their frequency in aldosterone-producing cell clusters of normal adrenal gland suggests a requirement for codriver mutations in APAs. Here we identified gain-of-function mutations in both CTNNB1 and GNA11 by whole-exome sequencing of 3/41 APAs. Further sequencing of known CTNNB1-mutant APAs led to a total of 16 of 27 (59%) with a somatic p.Gln209His, p.Gln209Pro or p.Gln209Leu mutation of GNA11 or GNAQ. Solitary GNA11 mutations were found in hyperplastic zona glomerulosa adjacent to double-mutant APAs. Nine of ten patients in our UK/Irish cohort presented in puberty, pregnancy or menopause. Among multiple transcripts upregulated more than tenfold in double-mutant APAs was LHCGR, the receptor for luteinizing or pregnancy hormone (human chorionic gonadotropin). Transfections of adrenocortical cells demonstrated additive effects of GNA11 and CTNNB1 mutations on aldosterone secretion and expression of genes upregulated in double-mutant APAs. In adrenal cortex, GNA11/Q mutations appear clinically silent without a codriver mutation of CTNNB1.

Keratinocytic epidermal nevi associated with localized fibro-osseous lesions without hypophosphatemia

Keratinocytic epidermal nevi (KEN) are characterized clinically by permanent hyperkeratosis in the distribution of Blaschko's lines and histologically by hyperplasia of epidermal keratinocytes. KEN with underlying RAS mutations have been associated with hypophosphatemic rickets and dysplastic bone lesions described as congenital cutaneous skeletal hypophosphatemia syndrome. Here, we describe two patients with keratinocytic epidermal nevi, in one associated with a papular nevus spilus, who presented with distinct localized congenital fibro-osseous lesions in the lower leg, diagnosed on both radiology and histology as osteofibrous dysplasia, in the absence of hypophosphatemia or rickets, or significantly raised FGF23 levels but with distinct mosaic HRAS mutations. This expands the spectrum of cutaneous/skeletal mosaic RASopathies and alerts clinicians to the importance of evaluating for bony disease even in the absence of bone profile abnormalities.

Misaligned foveal morphology and sector retinal dysfunction in AKT1-mosaic Proteus syndrome

PURPOSE

Proteus syndrome arises as a result of a post-zygotic mosaic activating mutation in the AKT1 oncogene, causing a disproportionate overgrowth of affected tissues. A small number of ocular complications have been reported. We present the unique findings in a patient who had molecular confirmation of AKT1 mosaicism alongside fulfilling the clinical criteria for Proteus syndrome.

METHODS

Pattern electroretinography, visual evoked potentials and multifocal electroretinography testing were performed alongside detailed retinal imaging and clinical examination to detail the ophthalmic characteristics.

RESULTS

Electrophysiological findings characterised unilateral macular dysfunction alongside sector retinal dysfunction of the right eye. This was demonstrated through optical coherence tomography and ultra-wide-field imaging to be associated with a misaligned foveal morphology and sector retinal dysfunction extending into the temporal retina.

CONCLUSION

We propose this patient has asymmetric foveal development and concomitant sector retinal dysfunction as the result of the mosaic AKT1 mutation, either through disruption in the retinal PI3K-AKT1 signalling pathway or through mechanical distortion of ocular growth, resulting in disproportionate inner retinal development. The findings expand the ocular phenotype of Proteus syndrome and encourage early assessment to identify any incipient ocular abnormalities.

Allele-Specific Small Interfering RNA Corrects Aberrant Cellular Phenotype in Keratitis-Ichthyosis-Deafness Syndrome Keratinocytes

Keratitis-ichthyosis-deafness (KID) syndrome is a severe, untreatable condition characterized by ocular, auditory, and cutaneous abnormalities, with major complications of infection and skin cancer. Most cases of KID syndrome (86%) are caused by a heterozygous missense mutation (c.148G>A, p.D50N) in the GJB2 gene, encoding gap junction protein Cx26, which alters gating properties of Cx26 channels in a dominant manner. We hypothesized that a mutant allele-specific small interfering RNA could rescue the cellular phenotype in patient keratinocytes (KCs). A KID syndrome cell line (KID-KC) was established from primary patient KCs with a heterozygous p.D50N mutation. This cell line displayed impaired gap junction communication and hyperactive hemichannels, confirmed by dye transfer, patch clamp, and neurobiotin uptake assays. A human-murine chimeric skin graft model constructed with KID-KCs mimicked patient skin in vivo, further confirming the validity of these cells as a model. In vitro treatment with allele-specific small interfering RNA led to robust inhibition of the mutant GJB2 allele without altering expression of the wild-type allele. This corrected both gap junction and hemichannel activity. Notably, allele-specific small interfering RNA treatment caused only low-level off-target effects in KID-KCs, as detected by genome-wide RNA sequencing. Our data provide an important proof-of-concept and model system for the potential use of allele-specific small interfering RNA in treating KID syndrome and other dominant genetic conditions.

Author Correction: Postzygotic inactivating mutations of RHOA cause a mosaic neuroectodermal syndrome

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Does the gene matter? Genotype-phenotype and genotype-outcome associations in congenital melanocytic naevi

Background

Genotype–phenotype studies can identify subgroups of patients with specific clinical features or differing outcomes, which can help shape management.

Objectives

To characterize the frequency of different causative genotypes in congenital melanocytic naevi (CMN), and to investigate genotype–phenotype and genotype–outcome associations.

Methods

We conducted a large cohort study in which we undertook MC1R genotyping from blood, and high‐sensitivity genotyping of NRAS and BRAF hotspots in 156 naevus biopsies from 134 patients with CMN [male 40%; multiple CMN 76%; projected adult size (PAS) > 20 cm, 59%].

Results

Mosaic NRAS mutations were detected in 68%, mutually exclusive with BRAF mutations in 7%, with double wild‐type in 25%. Two separate naevi were sequenced in five of seven patients with BRAF mutations, confirming clonality. Five of seven patients with BRAF mutations had a dramatic multinodular phenotype, with characteristic histology distinct from classical proliferative nodules. NRAS mutation was the commonest in all sizes of CMN, but was particularly common in naevi with PAS > 60 cm, implying more tolerance to that mutation early in embryogenesis. Facial features were less common in double wild‐type patients. Importantly, the incidence of congenital neurological disease, and apparently of melanoma, was not altered by genotype; no cases of melanoma were seen in BRAF‐mutant multiple CMN, however, this genotype is rare.

Conclusions

CMN of all sizes are most commonly caused by mutations in NRAS. BRAF is confirmed as a much rarer cause of multiple CMN, and appears to be commonly associated with a multinodular phenotype. Genotype in this cohort was not associated with differences in incidence of neurological disease in childhood. However, genotyping should be undertaken in suspected melanoma, for guidance of treatment.

What's already known about this topic?

Multiple congenital melanocytic naevi (CMN) have been shown to be caused by NRAS mosaic mutations in 70–80% of cases, by BRAF mosaicism in one case report and by inference in some previous cases.

There has been debate about genotypic association with different sizes of CMN, and no data on genotype–outcome.

What does this study add?

NRAS mosaicism was found in 68%, BRAF in 7% and double wild‐type in 25% of cases of CMN.

NRAS was the commonest mutation in all sizes of CMN, but was nearly universal in projected adult size > 60 cm.

BRAF is often associated with a distinct multinodular clinical/histological phenotype.

Adverse outcomes did not differ between genotypes on current numbers.

https://doi.org/10.1111/bjd.18747 available online

Final congenital melanocytic naevi colour is determined by normal skin colour and unaltered by superficial removal techniques: a longitudinal study

BACKGROUND

Spontaneous lightening of congenital melanocytic naevi (CMN) has not been studied systematically. Final colour is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth.

OBJECTIVES

To quantify the natural history of CMN lightening over time, and explore phenotypic and genotypic predictors of colour change.

METHODS

A longitudinal cohort study was undertaken of 110 patients with CMN (mean follow-up 5·3 years). Accurate colour-space measurements were taken from professional serial photographs of CMN and normal skin. Changes in colour over time were modelled using multiple logistic regression, against phenotypic and genotypic variables.

RESULTS

Lightening of CMN was significantly associated with lighter normal skin colour (P < 0·001) and with MC1R variant alleles (red/blonde hair gene) (P < 0·001), but not with CMN colour in the first 3 months of life, NRAS genotype or projected adult size of CMN. Importantly, the final colours of adjacent treated and untreated areas of CMN were indistinguishable.

CONCLUSIONS

Final CMN colour in childhood is related to the genetically determined skin colour of the individual, is unrelated to the colour of CMN at birth, and is unaffected by superficial removal. What's already known about this topic? Final colour of congenital melanocytic naevi (CMN) is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth. The phenomenon of spontaneous lightening in CMN, in which naevi lighten gradually and sometimes dramatically during childhood, has been described but not systematically studied. What does this study add? Final CMN colour in childhood is significantly associated with the individual's normal skin colour, and with MC1R genotype, and is therefore genetically determined. Final CMN colour is not predictable from CMN colour in the first 3 months of life. Superficial removal techniques do not alter the final colour of CMN.

Mosaic abnormalities of the skin: review and guidelines from the European Reference Network for rare skin diseases

BACKGROUND

Cutaneous mosaicism is an area of dermatology in which there has been an explosion of knowledge within the current decade. This has led to fundamental changes in the understanding of the conditions in this field, and to an ongoing paradigm shift in the approach to management of mosaic skin disorders.

OBJECTIVES

To lay out the general principles of mosaicism as they are currently understood, summarize the known cutaneous mosaic abnormalities of the skin with associated phenotypic and genotypic information, review the latest trials on targeted therapies and propose guidelines for the general approach to a patient with suspected mosaicism.

METHODS

This was a consensus expert review as part of the European Reference Network project (ERN-Skin).

CONCLUSIONS

This study provides clinicians with a practical approach to the patient with suspected mosaicism, redefines mosaicism for the modern genetic era, and proposes a new classification system based on genetic mechanism. What's already known about this topic? Cutaneous mosaicism is a complex field of dermatology that encompasses most birthmarks, and many rare syndromes. Some cutaneous patterns are known to be seen in mosaicism. Very few treatment options are available for most mosaic abnormalities of the skin. Recent high-sensitivity genetic techniques have led to an explosion of knowledge about genotype and phenotype in the literature. What does this study add? Expert consensus from the European Reference Network project. Review of knowledge of confirmed mosaic abnormalities of the skin, including cutaneous phenotype, extracutaneous associated features and genotype. Proposed new classification of mosaic abnormalities of the skin by genetic mechanism and therefore inheritance potential. Practical tips on correct sample collection and genetic investigation. Review of trials of targeted therapies. Guidelines for a practical clinical approach to the patient with suspected mosaicism.

Striking contiguous depigmentation across the lower limbs in piebaldism and its implications for understanding melanocytic migration and development

Piebaldism is a rare autosomal dominant disorder of pigmentation that is characterized by variable patches of depigmentation on the face, chest, abdomen, and extremities. We describe two cases of piebaldism, in whom the remarkable asymmetric distribution of the depigmented patches in a connected, contiguous pattern across the legs provides embryologic insights. This finding is not explained by the traditional theory that melanocytic migration only originates in the neural crest and progresses unilaterally down each leg. We propose that our cases, and other similar cases, can be explained by a recent theory of mesodermal melanocyte migration.

Aggressive melanoma in an infant with congenital melanocytic nevus syndrome and multiple, NRAS and BRAF mutation-negative nodules

We report the case of a newborn boy with multinodular NRAS and BRAF mutation-negative congenital melanocytic nevi and cerebral lesions compatible with congenital intraparenchymal melanosis. Histopathology from skin lesions showed atypical nodular melanocytic proliferation with marked melanocytic atypia and a large number of mitoses and apoptosis, indicating aggressive proliferation. The child developed several new subcutaneous tumors and multiple internal lesions, which were confirmed to be metastases, and died at 5 months of age. This case may represent an infantile melanoma developing from a giant congenital melanocytic nevus or a congenital melanoma.

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).

Widespread dynamic and pleiotropic expression of the melanocortin-1-receptor (MC1R) system is conserved across chick, mouse and human embryonic development

Background

MC1R, a G‐protein coupled receptor with high affinity for alpha‐melanocyte stimulating hormone (αMSH), modulates pigment production in melanocytes from many species and is associated with human melanoma risk. MC1R mutations affecting human skin and hair color also have pleiotropic effects on the immune response and analgesia. Variants affecting human pigmentation in utero alter the congenital phenotype of both oculocutaneous albinism and congenital melanocytic naevi, and have a possible effect on birthweight.

Methods and Results

By in situ hybridization, RT‐PCR and immunohistochemistry, we show that MC1R is widely expressed during human, chick and mouse embryonic and fetal stages in many somatic tissues, particularly in the musculoskeletal and nervous systems, and conserved across evolution in these three amniotes. Its dynamic pattern differs from that of TUBB3, a gene overlapping the same locus in humans and encoding class III β‐tubulin. The αMSH peptide and the transcript for its precursor, pro‐opiomelanocortin (POMC), are similarly present in numerous extra‐cutaneous tissues. MC1R genotyping of variants p.(V60M) and p.(R151C) was undertaken for 867 healthy children from the Avon Longitudinal Study of Parent and Children (ALSPAC) cohort, and birthweight modeled using multiple logistic regression analysis. A significant positive association initially found between R151C and birth weight, independent of known birth weight modifiers, was not reproduced when combined with data from an independent genome‐wide association study of 6,459 additional members of the same cohort.

Conclusions

These data clearly show a new and hitherto unsuspected role for MC1R in noncutaneous solid tissues before birth.

The patterns of birthmarks suggest a novel population of melanocyte precursors arising around the time of gastrulation

Systematic work in the mouse and chicken has mapped out two neural crest-derived pathways of melanocyte precursor migration. With these in mind, this study reappraises the patterns of congenital pigmentary disorders in humans and identifies three recurrent patterns consistent across genetically different diseases. Only two of these are seen in diseases known to be melanocyte cell-autonomous. The segmental pattern correlates well with the classical dorsolateral population from animal studies, demonstrating respect of the midline, cranio-caudal axial mixing, unilateral migration and involvement of key epidermally derived structures. Importantly however, the melanocyte precursors responsible for the non-segmental pattern, which demonstrates circular, bilateral migration centred on the midline, and not involving key epidermally derived structures, have not been identified previously. We propose that this population originates around the time of gastrulation, most likely within the mesoderm, and ultimately resides within the dermis. Whether it contributes to mature melanocytes in non-disease states is not known; however, parallels with the patterns of acquired vitiligo would suggest that it does. The third pattern, hypo- or hyperpigmented fine and whorled Blaschko's lines, is proposed to be non-cell-autonomous.

MEK inhibition appears to improve symptom control in primary NRAS-driven CNS melanoma in children

BACKGROUND

Primary melanoma of the CNS in children is extremely rare, and usually linked to congenital melanocytic naevus syndrome, caused by mosaicism for oncogenic NRAS mutations. Outcome is fatal in all cases. Data from murine and in vitro studies suggest that MEK inhibition is a possible therapeutic option.

METHODS

Four children with NRAS-mutated CNS melanoma were treated with Trametinib on a compassionate basis.

RESULTS

All four had an improvement in symptoms and objectively in signs. These varied from mild improvement for 1 month, to a sustained symptom-free period of 9 months in one case. In all cases there was eventual disease progression through treatment, followed by rapid death after discontinuation. There were no clinically-significant side effects.

CONCLUSIONS

Trametinib is the first therapy to show any objective or measurable effect in NRAS-mutated primary CNS melanoma, with few side effects in this small series. The role of this therapy should be explored further in this rare paediatric tumour.

Melanoma in congenital melanocytic naevi

Congenital melanocytic naevi (CMN) are a known risk factor for melanoma, with the greatest risk currently thought to be in childhood. There has been controversy over the years about the incidence of melanoma, and therefore over the clinical management of CMN, due partly to the difficulties of histological diagnosis and partly to publishing bias towards cases of malignancy. Large cohort studies have demonstrated that melanoma risk in childhood is related to the severity of the congenital phenotype. New understanding of the genetics of CMN offers the possibility of improvement in diagnosis of melanoma, identification of those at highest risk, and new treatment options. We review the world literature and our centre's experience over the last 25 years, including the molecular characteristics of melanoma in these patients and new melanoma incidence and outcome data from our prospective cohort. Management strategies are proposed for presentation of suspected melanoma of the skin and the central nervous system in patients with CMN, including use of oral mitogen-activated protein kinase kinase inhibitors in NRAS-mutated tumours.

Tissue Kallikrein Inhibitors Based on the Sunflower Trypsin Inhibitor Scaffold - A Potential Therapeutic Intervention for Skin Diseases

Tissue kallikreins (KLKs), in particular KLK5, 7 and 14 are the major serine proteases in the skin responsible for skin shedding and activation of inflammatory cell signaling. In the normal skin, their activities are controlled by an endogenous protein protease inhibitor encoded by the SPINK5 gene. Loss-of-function mutations in SPINK5 leads to enhanced skin kallikrein activities and cause the skin disease Netherton Syndrome (NS). We have been developing inhibitors based on the Sunflower Trypsin Inhibitor 1 (SFTI-1) scaffold, a 14 amino acids head-to-tail bicyclic peptide with a disulfide bond. To optimize a previously reported SFTI-1 analogue (I10H), we made five analogues with additional substitutions, two of which showed improved inhibition. We then combined those substitutions and discovered a variant (Analogue 6) that displayed dual inhibition of KLK5 (tryptic) and KLK7 (chymotryptic). Analogue 6 attained a tenfold increase in KLK5 inhibition potency with an Isothermal Titration Calorimetry (ITC) K_d of 20nM. Furthermore, it selectively inhibits KLK5 and KLK14 over seven other serine proteases. Its biological function was ascertained by full suppression of KLK5-induced Protease-Activated Receptor 2 (PAR-2) dependent intracellular calcium mobilization and postponement of Interleukin-8 (IL-8) secretion in cell model. Moreover, Analogue 6 permeates through the cornified layer of in vitro organotypic skin equivalent culture and inhibits protease activities therein, providing a potential drug lead for the treatment of NS.

Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans

Venous malformations (VMs) are painful and deforming vascular lesions composed of dilated vascular channels, which are present from birth. Mutations in the TEK gene, encoding the tyrosine kinase receptor TIE2, are found in about half of sporadic (nonfamilial) VMs, and the causes of the remaining cases are unknown. Sclerotherapy, widely accepted as first-line treatment, is not fully efficient, and targeted therapy for this disease remains underexplored. We have generated a mouse model that faithfully mirrors human VM through mosaic expression of Pik3ca(H1047R), a constitutively active mutant of the p110α isoform of phosphatidylinositol 3-kinase (PI3K), in the embryonic mesoderm. Endothelial expression of Pik3ca(H1047R)resulted in endothelial cell (EC) hyperproliferation, reduction in pericyte coverage of blood vessels, and decreased expression of arteriovenous specification markers. PI3K pathway inhibition with rapamycin normalized EC hyperproliferation and pericyte coverage in postnatal retinas and stimulated VM regression in vivo. In line with the mouse data, we also report the presence of activating PIK3CA mutations in human VMs, mutually exclusive with TEK mutations. Our data demonstrate a causal relationship between activating Pik3ca mutations and the genesis of VMs, provide a genetic model that faithfully mirrors the normal etiology and development of this human disease, and establish the basis for the use of PI3K-targeted therapies in VMs.

Mosaic Activating Mutations in GNA11 and GNAQ Are Associated with Phakomatosis Pigmentovascularis and Extensive Dermal Melanocytosis

Common birthmarks can be an indicator of underlying genetic disease but are often overlooked. Mongolian blue spots (dermal melanocytosis) are usually localized and transient, but they can be extensive, permanent, and associated with extracutaneous abnormalities. Co-occurrence with vascular birthmarks defines a subtype of phakomatosis pigmentovascularis, a group of syndromes associated with neurovascular, ophthalmological, overgrowth, and malignant complications. Here, we discover that extensive dermal melanocytosis and phakomatosis pigmentovascularis are associated with activating mutations in GNA11 and GNAQ, genes that encode Gα subunits of heterotrimeric G proteins. The mutations were detected at very low levels in affected tissues but were undetectable in the blood, indicating that these conditions are postzygotic mosaic disorders. In vitro expression of mutant GNA11^R183C and GNA11^Q209L in human cell lines demonstrated activation of the downstream p38 MAPK signaling pathway and the p38, JNK, and ERK pathways, respectively. Transgenic mosaic zebrafish models expressing mutant GNA11^R183C under promoter mitfa developed extensive dermal melanocytosis recapitulating the human phenotype. Phakomatosis pigmentovascularis and extensive dermal melanocytosis are therefore diagnoses in the group of mosaic heterotrimeric G-protein disorders, joining McCune-Albright and Sturge-Weber syndromes. These findings will allow accurate clinical and molecular diagnosis of this subset of common birthmarks, thereby identifying infants at risk for serious complications, and provide novel therapeutic opportunities.

Growth and hormone profiling in children with congenital melanocytic naevi

Background

Multiple congenital melanocytic naevi (CMN) is a rare mosaic RASopathy, caused by postzygotic activating mutations in NRAS. Growth and hormonal disturbances are described in germline RASopathies, but growth and hormone status have not previously been investigated in individuals with CMN.

Objectives

To explore premature thelarche, undescended testes, and a clinically abnormal fat distribution with CMN through prospective endocrinological assessment of a cohort of subjects with CMN, and a retrospective review of longitudinal growth of a larger group of patients with CMN from outpatient clinics (which included all subjects in the endocrinological assessment group).

Patients and methods

Longitudinal growth in a cohort of 202 patients with single or multiple CMN was compared with the U.K. National Child Measurement Programme 2010. Forty‐seven children had hormonal profiling including measurement of circulating luteinizing hormone, follicle‐stimulating hormone, thyroid stimulating hormone, adrenocorticotrophic hormone, growth hormone, prolactin, pro‐opiomelanocortin, estradiol, testosterone, cortisol, thyroxine, insulin‐like growth factor‐1 and leptin; 10 had oral glucose tolerance testing 25 had dual‐energy X‐ray absorptiometry scans for body composition.

Results

Body mass index increased markedly with age (coefficient 0·119, SE 0·016 standard deviation scores per year), at twice the rate of the U.K. population, due to increased adiposity. Three per cent of girls had premature thelarche variant and 6% of boys had persistent undescended testes. Both fat and muscle mass were reduced in areas underlying large naevi, resulting in limb asymmetry and abnormal truncal fat distribution. Anterior pituitary hormone profiling revealed subtle and variable abnormalities. Oral glucose tolerance tests revealed moderate–severe insulin insensitivity in five of 10, and impaired glucose tolerance in one.

Conclusions

Interpersonal variation may reflect the mosaic nature of this disease and patients should be considered individually. Postnatal weight gain is potentially related to the underlying genetic defect; however, environmental reasons cannot be excluded. Naevus‐related reduction of fat and muscle mass suggests local hormonal or metabolic effects on development or growth of adjacent tissues, or mosaic involvement of these tissues at the genetic level. Premature thelarche and undescended testes should be looked for, and investigated, as for any child.

What's already known about this topic?

CMN are caused by postzygotic mutations in the gene NRAS in the majority of cases, classifying it within the group of mosaic RASopathies.

Other germline and mosaic RASopathies are known to have growth and hormonal abnormalities.

No studies have been done on growth or endocrinology in children with CMN.

What does this study add?

Average body mass index increases markedly with age compared with the normal population; this is due to increased adiposity, and can be associated with insulin insensitivity.

Premature thelarche variant and persistent undescended testes are not infrequent findings, but puberty appears to develop normally.

Both fat and muscle mass can be reduced in areas underlying large naevi, resulting in asymmetry.

Linked Comment:Millington, Br J Dermatol 2015; 173: 1366–67.

Classification of neurological abnormalities in children with congenital melanocytic naevus syndrome identifies magnetic resonance imaging as the best predictor of clinical outcome

Background

The spectrum of central nervous system (CNS) abnormalities described in association with congenital melanocytic naevi (CMN) includes congenital, acquired, melanotic and nonmelanotic pathology. Historically, symptomatic CNS abnormalities were considered to carry a poor prognosis, although studies from large centres have suggested a much wider variation in outcome.

Objectives

To establish whether routine MRI of the CNS is a clinically relevant investigation in children with multiple CMN (more than one at birth), and to subclassify radiological abnormalities.

Methods

Of 376 patients seen between 1991 and 2013, 289 fulfilled our criterion for a single screening CNS MRI, which since 2008 has been more than one CMN at birth, independent of size and site of the largest naevus. Cutaneous phenotyping and radiological variables were combined in a multiple regression model of long‐term outcome measures (abnormal neurodevelopment, seizures, requirement for neurosurgery).

Results

Twenty‐one per cent of children with multiple CMN had an abnormal MRI. Abnormal MRI was the most significant predictor of all outcome measures. Abnormalities were subclassified into group 1 ‘intraparenchymal melanosis alone’ (n = 28) and group 2 ‘all other pathology’ (n = 18). Group 1 was not associated with malignancy or death during the study period, even when symptomatic with seizures or developmental delay, whereas group 2 showed a much more complex picture, requiring individual assessment.

Conclusions

For screening for congenital neurological lesions a single MRI in multiple CMN is a clinically relevant strategy. Any child with a stepwise change in neurological/developmental symptoms or signs should have an MRI with contrast of the brain and spine to look for new CNS melanoma.

What's already known about this topic?

Multiple congenital melanocytic naevi (CMN; more than one lesion at birth) can be associated with abnormalities of the central nervous system (CNS). The spectrum of these abnormalities includes congenital and acquired pathologies, melanotic and nonmelanotic lesions, rendering the term ‘CMN syndrome’ more appropriate than ‘neurocutaneous melanosis’.

Symptomatic CNS abnormalities were previously thought to carry a universally poor prognosis, although cohort data in the last decade have argued against this.

What does this study add?

A single CNS magnetic resonance imaging scan in multiple CMN, independent of projected adult size or site of the largest naevus, and ideally in the first 6 months of life, is currently an appropriate screening strategy.

An abnormal result is a better statistical predictor of clinical outcome than cutaneous phenotype.

Clinical management is altered as a result of the radiological result.

Acute Inhibition of MEK Suppresses Congenital Melanocytic Nevus Syndrome in a Murine Model Driven by Activated NRAS and Wnt Signaling

Congenital melanocytic nevus (CMN) syndrome is the association of pigmented melanocytic nevi with extra-cutaneous features, classically melanotic cells within the central nervous system, most frequently caused by a mutation of NRAS codon 61. This condition is currently untreatable and carries a significant risk of melanoma within the skin, brain, or leptomeninges. We have previously proposed a key role for Wnt signaling in the formation of melanocytic nevi, suggesting that activated Wnt signaling may be synergistic with activated NRAS in the pathogenesis of CMN syndrome. Some familial pre-disposition suggests a germ-line contribution to CMN syndrome, as does variability of neurological phenotypes in individuals with similar cutaneous phenotypes. Accordingly, we performed exome sequencing of germ-line DNA from patients with CMN to reveal rare or undescribed Wnt-signaling alterations. A murine model harboring activated NRAS(Q61K) and Wnt signaling in melanocytes exhibited striking features of CMN syndrome, in particular neurological involvement. In the first model of treatment for this condition, these congenital, and previously assumed permanent, features were profoundly suppressed by acute post-natal treatment with a MEK inhibitor. These data suggest that activated NRAS and aberrant Wnt signaling conspire to drive CMN syndrome. Post-natal MEK inhibition is a potential candidate therapy for patients with this debilitating condition.