**3.2 Telangiectasia**

The localized abnormal vascular formations that A-T patients show in several parts of their bodies—particularly in the eyes—is one of the most obvious and yet least investigated phenotypes of the disease [119]. Telangiectasia is highly prevalent in A-T, only missing in patients bearing mild ATM mutations that maintain some residual protein function [120]. Very little is known about the molecular mechanism that prompts telangiectasia when ATM is absent or dysfunctional. The current model proposes that oxidative stress caused by a lack of functional ATM may upregulate HIF1A levels, a hypoxia-activated transcription factor that can induce vascularization by increasing the levels of angiogenesis factor VEGF [120]. Intriguingly, SAPS also induces secretion of VEGF, suggesting a link between this DDR controlled pathway and vascularization [121, 122].
