Heterozygous Loss-of-Function Mutations in DLL4 Cause Adams-Oliver Syndrome

Abstract

Adams-Oliver syndrome (AOS) is a rare developmental disorder characterized by the presence of aplasia cutis congenita (ACC) of the scalp vertex and terminal limb-reduction defects. Cardiovascular anomalies are also frequently observed. Mutations in five genes have been identified as a cause for AOS prior to this report. Mutations in EOGT and DOCK6 cause autosomal-recessive AOS, whereas mutations in ARHGAP31, RBPJ, and NOTCH1 lead to autosomal-dominant AOS. Because RBPJ, NOTCH1, and EOGT are involved in NOTCH signaling, we hypothesized that mutations in other genes involved in this pathway might also be implicated in AOS pathogenesis. Using a candidate-gene-based approach, we prioritized DLL4, a critical NOTCH ligand, due to its essential role in vascular development in the context of cardiovascular features in AOS-affected individuals. Targeted resequencing of the DLL4 gene with a custom enrichment panel in 89 independent families resulted in the identification of seven mutations. A defect in DLL4 was also detected in two families via whole-exome or genome sequencing. In total, nine heterozygous mutations in DLL4 were identified, including two nonsense and seven missense variants, the latter encompassing four mutations that replace or create cysteine residues, which are most likely critical for maintaining structural integrity of the protein. Affected individuals with DLL4 mutations present with variable clinical expression with no emerging genotype-phenotype correlations. Our findings demonstrate that DLL4 mutations are an additional cause of autosomal-dominant AOS or isolated ACC and provide further evidence for a key role of NOTCH signaling in the etiology of this disorder.

Mapping Sites of O-Glycosylation and Fringe Elongation on Drosophila Notch

“…Moreover, mutations in human EOGT have been reported in an autosomal recessive form of a human disease called AdamsOliver syndrome (55,56). Notably, mutations in several Notch pathway components cause an autosomal dominant form of the same disease (39,40,(57)(58)(59). Together, these reports provide strong evidence that O-GlcNAcylation might modulate Notch signaling.…”

CdGAP/ARHGAP31, a Cdc42/Rac1 GTPase regulator, is critical for vascular development and VEGF-mediated angiogenesis

“…Interestingly, mutations in the DOCK6 gene encoding a Rac1/Cdc42 guanine nucleotide exchange factor responsible for an autosomal-recessive variant of AOS were recently associated with impaired vascular functions, supporting the importance of Rac1/Cdc42 signaling processes in vascular development4547. Furthermore, mutations in several genes of the Notch signaling pathway, including EOGT, RBPJ, Notch, and the Notch ligand Dll4, that encode important regulators of vascular development484950 were recently identified in AOS patients51525354. Together with our findings, these recent genetic studies converge towards two major altered signaling pathways in the etiology of the disorder, the Notch and Cdc42/Rac1 pathways, which may be interconnected to control the development of the embryonic vasculature55.…”

Notch Signaling in Vascular Smooth Muscle Cells

“… References: 1 Spinner et al (2001); 2 Eldadah et al (2001); 3 Meester et al (2015); 4 Stittrich et al (2014); 5 Garg et al (2005); 6 McDaniell et al (2006); 7 Simpson et al (2011); 8 Chabriat, Joutel, Dichgans, Tournier-Lasserve, and Bousser (2009); 9 Joutel et al (2000); 10 Joutel et al (1996); 11 Joutel et al (1997); 12 Gripp et al (2015); 13 Lee (2013); 14 Chida et al (2014); 15 Hassed et al (2012); 16 Shaheen et al (2013). …”