ORIGINAL PAPERS

Concordance of Genetic and Breath Tests for Lactose Intolerance in a Tertiary Referral Centre

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Marcin Krawczyk1,2, Malgorzata Wolska1,2, Stephanie Schwartz2, Frank Gruenhage2,3, Birgit Terjung2, Piero Portincasa4, Tilman Sauerbruch2, Frank Lammert2,3

1) Medical University of Lublin, Poland;
2) Department of Internal Medicine I, University Hospital Bonn, University of Bonn, Bonn, Germany;
3) Department of Medicine II, Saarland University Hospital, Saarland University, Homburg/Saar, Germany;
4) Clinica Medica "Augusto Murri", Department of Internal Medicine and Public Medicine, UniversitÓ degli Studi di Bari, Bari, Italy


Abstract

Background & Aims. Lactase non-persistence causes gastrointestinal symptoms after milk ingestion. Hydrogen breath test (BTH) and genotyping of a single nucleotide polymorphism (SNP) C>T 13,910 base pairs upstream of the lactase gene represent potential methods for diagnosis of this autosomal-recessive trait. The aim of the study was to compare the results of both tests in detecting lactose non-persistence in a tertiary referral centre. Patients. A group of 58 patients admitted to a German university hospital for symptoms suggesting lactose intolerance.

Methods.
BTH after lactose ingestion (50 g) and SNP -13,910C>T genotyping using single nucleotide primer extension (SNaPshot) technology (CC genotype - lactase non-persistence; TC/TT genotypes - lactase persistence).

Results.
Overall, 17 (29%) patients had a positive and 41 (71%) had a negative BTH result; 15 (26%) patients were CC-positive and 43 (74%) were CC-negative [28 (48%) TC; 15 (26%) TT]. The genotype frequencies did not deviate from the Hardy-Weinberg equilibrium. In the CC-positive group, concordance between both tests was 100%. In contrast, in the CC-negative group concordance was 95%, and positive BTH results could be attributed to other gastrointestinal pathologies in two patients. BTH had 100% negative predictive value, 88% positive predictive value, 100% sensitivity and 95% specificity, as compared to genetic testing.

Conclusions.
In carriers of the CC-genotype, BTH and genotyping correlate perfectly, and the genetic test provides an unambiguous result. In BTH-positive individuals with a negative genetic test there is good reason to suspect secondary causes of lactase deficiency.

Key words

Breath test - lactase - lactose intolerance - single nucleotide polymorphism.