Identification of the genetic bases of atypical Capillary Malformations
(2024)
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- Vascular Anomalies (VAs) arise from abnormalities in vascular development which result into locally malformed vessels. VAs are typically classified based on the type of vessel affected, the most common being venous malformations (VMs), lymphatic malformations (LMs), arteriovenous malformations (AVMs) and capillary malformations (CMs). However, several combined and syndromic phenotypes also exist. The advent of high-throughput sequencing technologies has facilitated the identification of somatic mutations and signaling pathways implicated in the pathogenesis of these conditions, with the two major ones being the PI3K/AKT/mTOR and the RAS/RAF/MAPK pathways. Signalling via these pathways is also often impaired in many types of cancers, prompting the idea of repurposing cancer drugs for the treatment of VAs as an alternative or complement to invasive procedures such as surgery or sclerotherapy. Although several key mutations contributing to the onset of VAs have been identified, many lesions, especially those affecting multiple structures, remain unexplained. This lack of understanding leaves affected patients without the option of targeted, noninvasive treatment. This thesis focuses on the identification of genes and mutations underlying so-called “atypical CMs”, validating such changes, and understanding the cellular and molecular mechanisms that contribute to the pathogenesis of the disease. The umbrella term “atypical CMs” regroups all those conditions characterized by CMs accompanied by additional, variable features. Unlike simple CMs, typically associated with GNAQ or GNA11 mutations, atypical CMs often lack a gene association. The absence of a precise clinical and genetic classification for these conditions frequently results in misdiagnosis, leading to suboptimal therapeutic strategies. In this study, we genetically characterized a clinical entity that we named CMDV (Capillary Malformation with Dilated Veins), associating it with somatic PIK3CA (non-hotspot) and PIK3R1 variants. Prior to this study, CMDV patients were classified as atypical, without any identified associated gene. PIK3R1 is a relatively novel gene in the context of VAs, reported only in few cases of vascular malformations characterized by extensive overgrowth. Using patient-derived ECs, we assessed the impact of two PIK3R1 mutations on the activation of PI3K/AKT/mTOR and RAS/RAF/MAPK pathways. Notably, we found that the activation of these pathways could be partially reversed by existing targeted drugs, including the PIK3CA-inhibitor Alpelisib, the AKT-inhibitor MK-2206, and the mTOR- inhibitor Sirolimus. Furthermore, in a zebrafish model, we showed that endothelial-specific expression of three PIK3R1 mutations could recapitulate the phenotype observed in patients, suggesting the potential use of this model for future drug screenings. Patients with complex phenotypes often face challenges in obtaining a conclusive diagnosis. Here, we present two patients with severe epilepsy along with atypical CMs, both found to harbor a somatic variant in the AKT3 gene. While vascular and cerebral anomalies are commonly linked to pathogenic variants in genes within the PI3K pathway, particularly PIK3CA, AKT3-related phenotypes remain still rare occurrences. Conducting genetic analysis, thus, contributed to expand the spectrum of AKT3-related diseases and facilitated the formulation of a precise diagnosis for these patients. Moreover, the identification of AKT3 as a gene underlying this condition, will potentially allow such patients to benefit from targeted therapies such as already available AKT-inhibitors. In conclusion, our findings increase our understanding on the genetic and molecular mechanisms underlying previously unclassified conditions. As we enter in the theragnostic era of treatment for VAs, genetic studies become of vital importance to ensure proper stratification and accurate diagnosis of patients, based not only on symptoms but also on genetic features. This provides valuable information for clinicians to determine the most suitable treatment.
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De Bortoli, M. (2024). Identification of the genetic bases of atypical Capillary Malformations. https://hdl.handle.net/2078.5/30575