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

From fish bowl to bedside: The power of zebrafish to unravel melanoma pathogenesis and discover new therapeutics

Melanoma is the most aggressive and deadliest form of skin cancer. A detailed knowledge of the cellular, molecular, and genetic events underlying melanoma progression is highly relevant to diagnosis, prognosis and risk stratification, and the development of new therapies. In the last decade, zebrafish have emerged as a valuable model system for the study of melanoma. Pathway conservation, coupled with the availability of robust genetic, transgenic, and chemical tools, has made the zebrafish a powerful model for identifying novel disease genes, visualizing cancer initiation, interrogating tumor-microenvironment interactions, and discovering new therapeutics that regulate melanocyte and melanoma development. In this review, we will give an overview of these studies, and highlight recent advancements that will help unravel melanoma pathogenesis and impact human disease.

Becker's Nevus and Lethal Beta-Actin Mutations

The etiology of Becker's nevus and Becker's nevus syndrome has been until now unknown. Cai et al. provide evidence that these disorders are caused by lethal mutations in ACTB, a gene coding for beta-actin. They hypothesize that these mutations may interfere with Hedgehog pathway signaling. Their findings have important implications for clinical genetics, and they open new aspects in hair research.

Intersection of diverse neuronal genomes and neuropsychiatric disease: The Brain Somatic Mosaicism Network

Neuropsychiatric disorders have a complex genetic architecture. Human genetic population-based studies have identified numerous heritable sequence and structural genomic variants associated with susceptibility to neuropsychiatric disease. However, these germline variants do not fully account for disease risk. During brain development, progenitor cells undergo billions of cell divisions to generate the ~80 billion neurons in the brain. The failure to accurately repair DNA damage arising during replication, transcription, and cellular metabolism amid this dramatic cellular expansion can lead to somatic mutations. Somatic mutations that alter subsets of neuronal transcriptomes and proteomes can, in turn, affect cell proliferation and survival and lead to neurodevelopmental disorders. The long life span of individual neurons and the direct relationship between neural circuits and behavior suggest that somatic mutations in small populations of neurons can significantly affect individual neurodevelopment. The Brain Somatic Mosaicism Network has been founded to study somatic mosaicism both in neurotypical human brains and in the context of complex neuropsychiatric disorders.

A somatic GNA11 mutation is associated with extremity capillary malformation and overgrowth

BACKGROUND

Capillary malformation is a cutaneous vascular anomaly that is present at birth, darkens over time, and can cause overgrowth of tissues beneath the stain. The lesion is caused by a somatic activating mutation in GNAQ. In a previous study, we were unable to identify a GNAQ mutation in patients with a capillary malformation involving an overgrown lower extremity. We hypothesized that mutations in GNA11 or GNA14, genes closely related to GNAQ, also may cause capillary malformations.

METHODS

Human capillary malformation tissue obtained from 8 patients that had tested negative for GNAQ mutations were studied. Lesions involved an extremity (n = 7) or trunk (n = 1). Droplet digital PCR (ddPCR) was used to detect GNA11 or GNA14 mutant cells (p.Arg183) in the specimens. Single molecule molecular inversion probe sequencing (smMIP-seq) was performed to search for other mutations in GNA11. Mutations were validated by subcloning and sequencing amplimers.

RESULTS

We found a somatic GNA11 missense mutation (c.547C > T; p.Arg183Cys) in 3 patients with a diffuse capillary malformation of an extremity. Mutant allelic frequencies ranged from 0.3 to 5.0%. GNA11 or GNA14 mutations were not found in 5 affected tissues or in unaffected tissues (white blood cell DNA).

CONCULSIONS

GNA11 mutations are associated with extremity capillary malformations causing overgrowth. Pharmacotherapy that affects GNA11 signaling may prevent the progression of capillary malformations.

Phacomatosis Cesioflammea with Cutis Marmorata-like Lesions and Unusual Extracutaneous Abnormalities: Is It a Distinct disorder?

A 2-month-old boy was presented with widespread lateralized blue macules (nevus cesius), an extensive nevus flammeus, and large patches of cutis marmorata telangiectatica congenita. Moreover, he had macrocephaly, a coarse facial appearance with depressed nasal bridge, retinal abnormalities, septal defects of the heart, and obliteration of the left brachiocephalic vein and major veins of the left arm with pronounced collateralization. The multisystem disorder of this boy cannot be categorized within the present classification of distinct types of phacomatosis pigmentovascularis. Although some similar complex cases have previously been reported, it seems too early to give them a specific name. Rather, the present case should be included, so far, into the group of unclassifiable types of phacomatosis pigmentovascularis.

GNA14 Somatic Mutation Causes Congenital and Sporadic Vascular Tumors by MAPK Activation

Vascular tumors are among the most common neoplasms in infants and children; 5%-10% of newborns present with or develop lesions within the first 3 months of life. Most are benign infantile hemangiomas that typically regress by 5 years of age; other vascular tumors include congenital tufted angiomas (TAs), kaposiform hemangioendotheliomas (KHEs), and childhood lobular capillary hemangiomas (LCHs). Some of these lesions can become locally invasive and unresponsive to pharmacologic intervention, leading to significant complications. Recent investigation has revealed that activating mutations in HRAS, KRAS, NRAS, GNAQ, and GNA11 can cause certain types of rare childhood vascular tumors, and we have now identified causal recurrent somatic activating mutations in GNA14 by whole-exome and targeted sequencing. We found somatic activating GNA14 c.614A>T (p.Gln205Leu) mutations in one KHE, one TA, and one LCH and a GNA11 c.547C>T (p.Arg183Cys) mutation in two LCH lesions. We examined mutation pathobiology via expression of mutant GNA14 or GNA11 in primary human endothelial cells and melanocytes. GNA14 and GNA11 mutations induced changes in cellular morphology and rendered cells growth-factor independent by upregulating the MAPK pathway. Our findings identify GNA14 mutations as a cause of childhood vascular tumors, offer insight into mechanisms of oncogenic transformation by mutations affecting Gaq family members, and identify potential targets for therapeutic intervention.

Somatic Activating Mutations in GNAQ and GNA11 Are Associated with Congenital Hemangioma

Congenital hemangioma is a rare vascular tumor that forms in utero. Postnatally, the tumor either involutes quickly (i.e., rapidly involuting congenital hemangioma [RICH]) or partially regresses and stabilizes (i.e., non-involuting congenital hemangioma [NICH]). We hypothesized that congenital hemangiomas arise due to somatic mutation and performed massively parallel mRNA sequencing on affected tissue from eight participants. We identified mutually exclusive, mosaic missense mutations that alter glutamine at amino acid 209 (Glu209) in GNAQ or GNA11 in all tested samples, at variant allele frequencies (VAF) ranging from 3% to 33%. We verified the presence of the mutations in genomic DNA using a combination of molecular inversion probe sequencing (MIP-seq) and digital droplet PCR (ddPCR). The Glu209 GNAQ and GNA11 missense variants we identified are common in uveal melanoma and have been shown to constitutively activate MAPK and/or YAP signaling. When we screened additional archival formalin-fixed paraffin-embedded (FFPE) congenital cutaneous and hepatic hemangiomas, 4/8 had GNAQ or GNA11 Glu209 variants. The same GNAQ or GNA11 mutation is found in both NICH and RICH, so other factors must account for these tumors' different postnatal behaviors.

Epileptogenesis in neurocutaneous disorders with focus in Sturge Weber syndrome

Epilepsy is a major morbidity in Sturge Weber syndrome, a segmental vascular neurocutaneous disorder classically associated with facial angiomas, glaucoma, and leptomeningeal capillary-venous type vascular malformations. The extent of the latter correlates with neurological outcome. Post-zygotic mosaicism for the activating mutation p.R183Q of the GNAQ gene has been identified as the major cause.  GNAQ encodes for an alpha subunit of a heterotrimeric G protein critical to blood vessel development. The earlier the timing of the mutation in development, the more severe the involvement, e.g. from isolated port-wine stains to the full syndrome. The strongest predictors of adverse outcomes are MRI and the presence of angiomas involving any part of the forehead, delineated inferiorly from the outer canthus of the eye to the top of the ear, and including the upper eyelid.  The neurological course may be progressive and the typical constellation of symptoms is focal onset seizures, hemiparesis, headache, stroke-like episodes, behavior problems, intellectual disability, and visual field deficits. Antiseizure medications are effective in about half of patients. The presence of localized seizures, focal neurological deficits, and drug resistant epilepsy indicate epilepsy surgical evaluation. Earlier seizure onset, i.e. before six months of age, is associated with a more severe course with significant residual deficits. Factors contributing to epileptogenesis include decreased brain tissue perfusion due to abnormal venous drainage, anoxic injury contributing to cerebral calcification, breakdown of the blood-brain barrier, and the presence of developmental cortical malformations. Pre-symptomatic prophylactic treatment may be a future option to modify the course of the disease including the associated epileptogenesis.