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.

RNA therapy for oncogenic NRAS-driven naevi induces apoptosis.

RAS proteins regulate cell division, differentiation and apoptosis via multiple downstream effector pathways. Oncogenic RAS variants are the commonest drivers in cancers, however they also drive many benign lesions predisposing to malignancy, such as melanocytic naevi, thyroid nodules, and colonic polyps. Reversal of these benign lesions could reduce cancer incidence, however the effects of oncogenic RAS have been notoriously difficult to target with downstream pathway inhibitors. Here we show effective suppression of oncogenic and currently undruggable NRASQ61K in primary cells from melanocytic naevi using siRNA targeted to the recurrent causal variant. This results in striking reduction in expression of ARL6IP1, a known inhibitor of endoplasmic reticulum stress-induced apoptosis not previously linked to NRAS. We go on to show that a single dose of siRNA in primary cells triggers an apoptotic cascade, in contrast to treatment with a MEK inhibitor. Protective packaging of the targeted siRNA into lipid nanoparticles permits successful delivery into a humanised mouse model of melanocytic naevi, and results in variant NRAS knockdown in vivo. These data show that RAS-induced protection from apoptosis is involved in persistence of NRAS-driven melanocytic naevi and anticipate that targeted siRNA could form the basis of clinical trials for RAS-driven benign tumours.

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.