Question: A 55-year-old man, the father of a celiac son, with iron deficiency anemia and a recent increase in the rhythm of deposition, has been determined to have a negative HLA-DQ2 and HLADQ8 allele. Which diagnostic study is the most appropriate in this case? 
 Options:  <1> Determination of IgA anti-transglutaminase antibodies. <2> Upper digestive endoscopy with taking of duodenal biopsies. <3> D-xylose test. <4> Evaluate the response to a gluten-free diet. <5> Colonoscopy
5