Concordance of Genetic and Breath Tests for Lactose Intolerance
in a Tertiary Referral Centre
Full Article (PDF file)
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,
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.
Breath test - lactase - lactose intolerance - single nucleotide