The acronym PHACE (posterior fossa anomalies, infantile hemangiomas, arterial anomalies, cardiac defects and eye anomalies) was coined to describe the features of an uncommon sporadic condition with a vascular tumor (infantile hemangioma), developmental and progressive vascular abnormalities. Here, we report the findings of our analysis of whole genome sequencing of germline samples from 98 unrelated trios in which the probands had PHACE. Two coding variants, RASA3–p.Val85Met and THBS2–p.Asp859Asn, were predicted to be pathogenic by numerous algorithms. This analysis was negative for a shared gene across multiple probands; however, a g:Profiler pathway analysis of the genes with rare, de novo variants demonstrated combinatorial variants in the RAS/MAPK pathway. Coding and noncoding variants in six RAS pathway genes were prioritized based on the vascular abnormalities reported in knockout mouse models. To identify lineages in which the genes may be acting, we explored the expression of the prioritized candidate genes RASA3, AFF2, DLC1, EPHA3, PIK3CA, and THBS2 across diverse cell types in the human developing heart by incorporating chromatin accessibility (scATAC-seq) and gene expression (scRNA-seq) datasets. We observed that AFF2, EPHA3, PIK3CA, and THBS2 are co-expressed in the vascular smooth muscle cells in the fetal heart, whilst AFF2, EPHA3, and PIK3CA are co-expressed in the vascular endothelium. These findings suggest oligogenic variants in RAS pathway genes may contribute to the developmental vascular abnormalities in PHACE.

BACKGROUND:Pseudoxanthoma elasticum (PXE) manifests with cutaneous lesions consisting of yellowish papules coalescing into plaques of inelastic skin. Histopathology demonstrates accumulation of pleiomorphic elastic structures with progressive mineralization. The classic form of PXE is caused by mutations in the ABCC6 gene. OBJECTIVES:A 2-year-old patient with PXE of the neck, inguinal folds and lower abdomen, and with extensive tissue mineralization, was evaluated for the underlying mutations in candidate genes known to be involved in ectopic mineralization disorders. METHODS:The patient's genotype was studied by sequencing ABCC6, MGP and ENPP1 genes, encoding proteins which harbour mutations in ectopic mineralization disorders. RESULTS:No pathogenetic mutations were found in the ABCC6 or MGP genes. Sequencing of ENPP1 disclosed a homozygous missense mutation, p.Y513C, associated with generalized arterial calcification of infancy. CONCLUSIONS:This study demonstrates the presence of the cutaneous features of PXE in a genetically distinct disease, generalized arterial calcification of infancy, and thus expands the spectrum of PXE-related disorders.