*3.2. Epistaxis*

The most common clinical manifestation of HHT in pediatric patients was spontaneous recurrent epistaxis, present among 172/205 (83.9%) of our patients. There was no significant association between genotype and the presence of epistaxis (*p* = 0.865).


**Table 1.** Demographic and clinical characteristics of pediatric HHT patients.

1 Combined phenotype: combined presence of both pulmonary AVM(s) and brain VM(s). HHT: hereditary hemorrhagic Telangiectasia; VM: vascular malformation; AVM: Arteriovenous malformation; GI: gastrointestinal.

#### *3.3. Mucocutaneous Telangiectases*

Approximately half (50.7%) of patients in our cohort had typical mucocutaneous telangiectases. The prevalence by genotype was almost equivalent between patients with *ENG* and *ACVRL1* mutations at 46.5% and 47.5%, respectively. Four (36.4%) patients with a *SMAD4* mutation had typical mucocutaneous telangiectases. There was no significant association between genotype and the presence of telangiectasia (*p* = 0.790).

#### *3.4. GI Bleeding*

A history of GI bleeding was reported in 9/205 (4.4%) patients. Patients with a *SMAD4* mutation were significantly more likely to experience GI bleeding (*p* < 0.001), compared to patients with *ENG* or *ACVRL1* mutations. Clinical and endoscopic data was available in 7/9 (77.8%) patients with GI bleeding. All 7/7 (100%) had lower GI bleeding; none reported upper GI bleeding. In 5/7 (71.4%) patients, polyps were identified as the cause of GI bleeding. No cause was identified in the remaining 2/7 (28.6%) patients with GI bleeding and GI bleeding resolved spontaneously
