The aim of this study is to assess effect of gluten on the gut barrier function in patients at high risk for celiac disease and non-celiac gluten sensitivity (NCGS) patients. This study will assess the gut permeability in three groups of patients 1) children who are at high risk for developing celiac disease (CD) (siblings of patients with celiac disease), 2) Children who are self-diagnosed with NCGS and 3) control group of patients matched for age and gender. Patients will undergo celiac serologic and genetic testing, after which the rhamnose test will be performed to assess the presence of increased gut permeability.