Vascular anomalies are variably associated with overgrowth, skeletal anomalies, and abnormalities of the brain, leptomeninges, and eye. We assembled a 16-institution network to determine the range of genetic variants associated with a spectrum of vascular anomalies with overgrowth, ranging from mild to severe. Because of the overlap between cancer-associated variants and previously described somatic variants in vascular overgrowth syndromes, we employed tumor genetic profiling via high-depth next-generation sequencing using a panel to assay affected tissue from a diverse cohort of subjects with vascular anomalies with overgrowth. Seventy-five percent (43/57) harbored pathogenic or likely pathogenic variants in 10 genes. We identified two genes (mTOR, PIK3R1) and several variants previously described in the setting of cancer but that, to our knowledge, have not been described in vascular malformations. All were identified at low variant allele frequency consistent with somatic mosaic etiology. By leveraging somatic variant detection technology typically applied to cancer in a cohort inclusive of broad phenotypic severity, we demonstrated that most vascular anomalies with overgrowth harbor postzygotic gain-of-function mutations in oncogenes. Furthermore, continued interrogation of oncogenes in benign developmental disorders could provide insight into fundamental mechanisms regulating cell growth.

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Dr Adotama and Mr Tinker had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Adotama, Glass, Allen.

Capillary malformation-arteriovenous malformation (CM-AVM) syndrome, due to inactivating mutations in RASA1 in 68% of cases, is characterized by the development of cutaneous capillary malformations and arteriovenous malformations or fistulas; no known genetic etiology has been identified in patients with CM-AVM syndrome without RASA1 mutations. We present the case of a child with RASA1-negative CM-AVM syndrome with a de novo missense mutation in EPHB4, a transmembrane tyrosine kinase receptor essential for vasculogenesis. Inactivating the mutation in EPHB4 has been shown to upregulate the mitogen-activated protein kinase pathway and the mammalian target of rapamycin complex 1, possibly contributing to the development of vascular malformations.