A NOTCH3 homozygous nonsense mutation in familial Sneddon syndrome with pediatric stroke

Sneddon syndrome is a rare disorder affecting small and medium-sized blood vessels that is characterized by the association of livedo reticularis and stroke. We performed whole-exome sequencing (WES) in 2 affected siblings of a consanguineous family with childhood-onset stroke and identified a homozygous nonsense mutation within the epidermal growth factor repeat (EGFr) 19 of NOTCH3, p.(Arg735Ter). WES of 6 additional cases with adult-onset stroke revealed 2 patients carrying heterozygous loss-of-function variants in putative NOTCH3 downstream genes, ANGPTL4, and PALLD. Our findings suggest that impaired NOTCH3 signaling is one underlying disease mechanism and that bi-allelic loss-of-function mutation in NOTCH3 is a cause of familial Sneddon syndrome with pediatric stroke.

A Novel Mechanism for Wnt Activation of Canonical Signaling through the LRP6 Receptor

ABSTRACT LDL receptor-related protein 6 (LRP6) is a Wnt coreceptor in the canonical signaling pathway, which plays essential roles in embryonic development. We demonstrate here that wild-type LRP6 forms an inactive dimer through interactions mediated by epidermal growth factor repeat regions within the extracellular domain. A truncated LRP6 comprising its transmembrane and cytoplasmic domains is expressed as a constitutively active monomer whose signaling ability is inhibited by forced dimerization. Conversely, Wnts are shown to activate canonical signaling through LRP6 by inducing an intracellular conformational switch which relieves allosteric inhibition imposed on the intracellular domains. Thus, Wnt canonical signaling through LRP6 establishes a novel mechanism for receptor activation which is opposite to the general paradigm of ligand-induced receptor oligomerization.