EVALUATION OF AGREEMENT BETWEEN C/T-13910 POLYMORPHISM GENOTYPING RESULTS AND LACTOSE TOLERANCE TEST RESULTS: A RETROSPECTIVE POPULATION-BASED STUDY IN BRAZIL.

Background: Lactose tolerant test (LTT) is the most broadly used diagnostic test for lactose intolerance in Brazil, is an indirect, minimally invasive and a low-cost test that is widely available in primary care and useful in clinical practice. The C/T-13910 polymorphism in lactase persistence has been well characterized in Caucasian populations, but there are no studies evaluating the concordance between C/T-13910 polymorphism genotyping results and LTT results in Brazil, where the population is highly mixed.

Objective: We aimed to evaluate agreement between presence of C/T-13910 polymorphism genotyping and malabsorption in LTT results.

Methods: This is a retrospective analysis of a Brazilian population whose data were collected from a single laboratory database present in several Brazilian states. Results of individuals who underwent both genetic testing for lactose intolerance (C/T-13910 polymorphism genotyping) and an LTT from April 2016 until February 2019 were analysed to evaluate agreement between tests. Groups were classified according to age (<10-year-old (yo), 10-17 yo, ≥18 yo groups) and state of residence (São Paulo or Rio Grande do Sul). Results: Among the 404 patients evaluated, there was agreement between the genotyping and LTT results in 325 (80.4%) patients and discordance in 79 (19.6%) patients (k=0.42 -moderate agreement). Regarding the genotype, 47 patients with genotype C/C (lactase nonpersistence) had normal LTT results, and 32 with genotype C/T or T/T (indicating lactase persistence) had abnormal LTT results. Neither age nor state of residence (Rio Grande do Sul or São Paulo) affected the agreement between test results.

Conclusion: Considering the moderate agreement between C/T-13910 polymorphism genotyping and LTT results (κ=0.42) in the Brazilian population, we hypothesize that an analysis of other polymorphisms could be a strategy to improve the agreement between genotyping and established tests and suggest that additional studies should focus on exploring this approach.

Background: • Lactose intolerance is highly prevalent and may be implicated as a cofactor, or as a differential diagnosis, in many gastrointestinal conditions.

Background: • The C/T-13910 polymorphism in lactase persistence is well characterized in Caucasian populations for lactase persistence.

Background: • Concordance between genotyping and functional tests does not occur in all patients.

Background: • Brazil has a highly mixed population and knowledge regarding presence of other polymorphisms is of importance in clarifying difficult cases.