Young H. Lim

Multilineage somatic activating mutations in HRAS and NRAS cause mosaic cutaneous and skeletal lesions, elevated FGF23 and hypophosphatemia

Pathologically elevated serum levels of fibroblast growth factor-23 (FGF23), a bone-derived hormone that regulates phosphorus homeostasis, result in renal phosphate wasting and lead to rickets or osteomalacia. Rarely, elevated serum FGF23 levels are found in association with mosaic cutaneous disorders that affect large proportions of the skin and appear in patterns corresponding to the migration of ectodermal progenitors. The cause and source of elevated serum FGF23 is unknown. In those conditions, such as epidermal and large congenital melanocytic nevi, skin lesions are variably associated with other abnormalities in the eye, brain and vasculature. The wide distribution of involved tissues and the appearance of multiple segmental skin and bone lesions suggest that these conditions result from early embryonic somatic mutations. We report five such cases with elevated serum FGF23 and bone lesions, four with large epidermal nevi and one with a giant congenital melanocytic nevus. Exome sequencing of blood and affected skin tissue identified somatic activating mutations of HRAS or NRAS in each case without recurrent secondary mutation, and we further found that the same mutation is present in dysplastic bone. Our finding of somatic activating RAS mutation in bone, the endogenous source of FGF23, provides the first evidence that elevated serum FGF23 levels, hypophosphatemia and osteomalacia are associated with pathologic Ras activation and may provide insight in the heretofore limited understanding of the regulation of FGF23.

Somatic Activating RAS Mutations Cause Vascular Tumors Including Pyogenic Granuloma

Young H. Lim1,2,5, Stephanie R. Douglas3, Christine J. Ko1,2, Richard J. Antaya1,4, Jennifer M. McNiff1,2, Jing Zhou1,2,5, Yale Center for Genome Analysis, Keith A. Choate1,2,5,*, and Deepak Narayan3,* 1Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut, USA 2Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, USA 3Section of Plastic Surgery, Department of Surgery, Yale University School of Medicine, New Haven, Connecticut, USA

Assembling a protein-protein interaction map of the SSU processome from existing datasets.

Background The small subunit (SSU) processome is a large ribonucleoprotein complex involved in small ribosomal subunit assembly. It consists of the U3 snoRNA and ∼72 proteins. While most of its components have been identified, the protein-protein interactions (PPIs) among them remain largely unknown, and thus the assembly, architecture and function of the SSU processome remains unclear. Methodology We queried PPI databases for SSU processome proteins to quantify the degree to which the three genome-wide high-throughput yeast two-hybrid (HT-Y2H) studies, the genome-wide protein fragment complementation assay (PCA) and the literature-curated (LC) datasets cover the SSU processome interactome. Conclusions We find that coverage of the SSU processome PPI network is remarkably sparse. Two of the three HT-Y2H studies each account for four and six PPIs between only six of the 72 proteins, while the third study accounts for as little as one PPI and two proteins. The PCA dataset has the highest coverage among the genome-wide studies with 27 PPIs between 25 proteins. The LC dataset was the most extensive, accounting for 34 proteins and 38 PPIs, many of which were validated by independent methods, thereby further increasing their reliability. When the collected data were merged, we found that at least 70% of the predicted PPIs have yet to be determined and 26 proteins (36%) have no known partners. Since the SSU processome is conserved in all Eukaryotes, we also queried HT-Y2H datasets from six additional model organisms, but only four orthologues and three previously known interologous interactions were found. This provides a starting point for further work on SSU processome assembly, and spotlights the need for a more complete genome-wide Y2H analysis.

Symptomatic Congenital Hemangioma and Congenital Hemangiomatosis Associated With a Somatic Activating Mutation in GNA11.

IMPORTANCE Congenital hemangiomas are uncommon benign vascular tumors that present fully formed at birth. They are rarely associated with transient hematologic abnormalities, which are typically less severe than the Kasabach-Merritt phenomenon associated with kaposiform hemangioendotheliomas. Congenital hemangiomas are typically solitary and have not been reported to occur in a multifocal, generalized pattern. OBJECTIVE To describe a male infant born with an unusual, large vascular mass complicated by anemia, thrombocytopenia, and disseminated intravascular coagulopathy, as well as innumerable small vascular papules in a generalized cutaneous distribution. DESIGN, SETTING, AND PARTICIPANT This case report is a descriptive observation of the results of clinical, pathologic, and genetic studies performed in a single male infant observed for 2 years (May 2013 to June 2015) for vascular anomalies at a tertiary care referral center. MAIN OUTCOMES AND MEASURES Histopathologic, immunohistochemical, and genetic study results of tumor specimens and saliva. RESULTS Careful pathologic study of 3 tumor specimens revealed similar lobular proliferations of bland endothelial cells. Lesional vessels did not express GLUT1 or the lymphatic marker D2-40, whereas WT1 was expressed. A somatic c.A626C, p.Q209P mutation in the GNA11 gene was identified in tumoral tissue. CONCLUSIONS AND RELEVANCE These findings support a unifying diagnosis of congenital hemangioma for these vascular tumors. To date, this is the first-reported case of a hemangiomatosis presentation of congenital hemangioma. In addition to highlighting this novel phenotype, this case indicates the rare association of congenital hemangioma with hematologic abnormalities and verifies somatic activating mutations as the underlying cause of congenital hemangioma.

Somatic p.T771R KDR (VEGFR2) Mutation Arising in a Sporadic Angioma During Ramucirumab Therapy.

IMPORTANCE Inhibition of angiogenesis is an effective anticancer strategy because neoplasms require a rich blood supply. Ramucirumab, approved by the US Food and Drug Administration in 2014 to treat gastric adenocarcinomas and non-small cell lung carcinomas, targets vascular endothelial growth factor 2 (VEGFR2). We identified a patient prescribed a regimen of irinotecan hydrochloride, cetuximab, and ramucirumab for metastatic rectal cancer (diagnosed in November 2013 and treated through early January 2015) who developed a new-onset, expanding vascular lesion on his right leg. Via exome sequencing, we found that the lesion contained a single somatic mutation in KDR (encodes VEGFR2), possibly in response to ramucirumab. Vascular tumors are not a known complication of antiangiogenic therapeutics. OBSERVATIONS Exome sequencing of the well-demarcated, blanching vascular lesion on the lateral right shin revealed a somatic p.T771R mutation in KDR, without evidence of other somatic mutations or loss of heterozygosity. Histological features included lobules of small vessels within the dermis, resembling a tufted angioma. CONCLUSIONS AND RELEVANCE A potential adverse effect of ramucirumab in combination therapy is the development of sporadic angiomas. The p.T771R mutation was previously implicated in autophosphorylation of VEGFR2 and reported in angiosarcomas alongside other driver mutations. Our observations suggest that this mutation confers a proliferative advantage in the setting of ramucirumab therapy. Patients receiving ramucirumab should be monitored for the development of new vascular lesions.

Revertant mosaicism in genodermatoses

Inherited monogenic skin disorders include blistering disorders, inflammatory disorders, and disorders of differentiation or development. In most cases, the skin is broadly involved throughout the affected individual’s lifetime, but rarely, appearance of normal skin clones has been described. In these cases of revertant mosaicism, cells undergo spontaneous correction to ameliorate the effects of genetic mutation. While targeted reversion of genetic mutation would have tremendous therapeutic value, the mechanisms of reversion in the skin are poorly understood. In this review, we provide an overview of genodermatoses that demonstrate widespread reversion and their corrective mechanisms, as well as the current research aimed to understand this “natural gene therapy”.

Mass Spectrometry Imaging Can Distinguish on a Proteomic Level Between Proliferative Nodules Within a Benign Congenital Nevus and Malignant Melanoma.

Abstract: Histopathological interpretation of proliferative nodules occurring in association with congenital melanocytic nevi can be very challenging due to their similarities with congenital malignant melanoma and malignant melanoma arising in association with congenital nevi. We hereby report a diagnostically challenging case of congenital melanocytic nevus with proliferative nodules and ulcerations, which was originally misdiagnosed as congenital malignant melanoma. Subsequent histopathological examination in consultation by one of the authors (R.L.) and mass spectrometry imaging analysis rendered a diagnosis of congenital melanocytic nevus with proliferative nodules. In this case, mass spectrometry imaging, a novel method capable of distinguishing benign from malignant melanocytic lesions on a proteomic level, was instrumental in making the diagnosis of a benign nevus. We emphasize the importance of this method as an ancillary tool in the diagnosis of difficult melanocytic lesions.

Keratoacanthoma Shares Driver Mutations with Cutaneous Squamous Cell Carcinoma

(Kaplan et al., 2008; Udey et al., 2008). From a clinical point of view this could make sense, becauseT-cell responses are often more hazardous than protective, and the presence of cells counteracting such immune reactions could be beneficial (Schwarz, 2010). The results of this study suggest that LCs are negatively regulated by UCA, representing another level of control on cutaneous immune reactions. Accordingly, it was reported that in the epidermis of patients with atopic dermatitis who have reduced UCA levels because of mutations in the filaggrin gene, more mature LCs were observed than in patients with atopic dermatitiswithwild type filaggrin (Leitch et al., 2016). Although our results are compatible with the fact that cis-UCA is an important mediator of UV-induced immunosuppression, they also indicate that transUCA exerts negative regulatory effects on LCs in nonirradiated skin. Further studies are necessary to define the roles of both isomers of endogenous UCA and their mechanisms of action in pathophysiological contexts.

Mosaicism in Cutaneous Disorders

Genetic mosaicism arises when a zygote harbors two or more distinct genotypes, typically due to de novo, somatic mutation during embryogenesis. The clinical manifestations largely depend on the differentiation status of the mutated cell; earlier mutations target pluripotent cells and generate more widespread disease affecting multiple organ systems. If gonadal tissue is spared-as in somatic genomic mosaicism-the mutation and its effects are limited to the proband, whereas mosaicism also affecting the gametes, such as germline or gonosomal mosaicism, is transmissible. Mosaicism is easily appreciated in cutaneous disorders, as phenotypically distinct mutant cells often give rise to lesions in patterns determined by the affected cell type. Genetic investigation of cutaneous mosaic disorders has identified pathways central to disease pathogenesis, revealing novel therapeutic targets. In this review, we discuss examples of cutaneous mosaicism, approaches to gene discovery in these disorders, and insights into molecular pathobiology that have potential for clinical translation.

Mutations in PERP cause dominant and recessive keratoderma

Investigation of genetic determinants of Mendelian skin disorders has substantially advanced understanding of epidermal biology. Here we show that mutations in PERP, encoding a crucial component of desmosomes, cause both dominant and recessive human keratoderma. Heterozygosity for a C-terminal truncation, which produces a protein that appears to be unstably incorporated into desmosomes, causes Olmsted syndrome with severe periorificial and palmoplantar keratoderma in multiple unrelated kindreds. Homozygosity for an N-terminal truncation ablates expression and causes widespread erythrokeratoderma, with expansion of epidermal differentiation markers. Both exhibit epidermal hyperproliferation, immature desmosomes lacking a dense midline observed via electron microscopy, and impaired intercellular adhesion upon mechanical stress. Localization of other desmosomal components appears normal, which is in contrast to other conditions caused by mutations in genes encoding desmosomal proteins. These discoveries highlight the essential role of PERP in human desmosomes and epidermal homeostasis and further expand the heterogeneous spectrum of inherited keratinization disorders.