Tests for endoglin up-regulation in activated monocytes were performed in blood samples from six HHT2 patients in a single affected family.
6B emphasize that the expression index for endoglin up-regulation in those HHT2 patients is age-dependent, as compared with controls.
Haploinsufficiency is the molecular basis currently accepted for the clinical manifestations in HHT1 and HHT2 patients (3, 20, 22).
The relative deficiency of endoglin in activated monocytes from HHT1 patients is expected and has been used as complementary to endoglin analysis in HUVECs (newborns) and in mutation studies to differentiate between HHT1 and HHT2 families (10).
The down-regulation of endoglin in activated monocytes derived from HHT2 patients contrasts with a previous report (22) in which endoglin concentrations remained unaffected in HHT2 patients.
Hence, decreased concentrations of functional ALK1 receptor in HHT2 patients may also lead to improper endoglin up-regulation in monocytes.
From a pathogenic point of view, deficient up-regulation of endoglin in HHT2 patients suggests important consequences, i.e., that endoglin haploinsufficiency is the ultimate trigger mechanism underlying not only HHT1, but also HHT2.