Evaluation of a new DNA test compared with the lactose hydrogen breath test for the diagnosis of lactase non-persistence.

BACKGROUND AND AIMS: Recent publications have found that the CC genotype of the DNA variant -13910 T/C upstream of the LCT gene is associated with lactase non-persistence. We therefore compared the value of DNA testing for this variant (DNA test) with the lactose hydrogen breath test (H2 test), which is the clinical standard for the diagnosis of lactase non-persistence. PATIENTS AND METHODS: One hundred and twenty-three consecutive patients with suspected lactose malabsorption were tested for the presence of the -13910 T/C variant by polymerase chain reaction-restriction fragment length polymorphism analysis. These patients also underwent the H2 test after ingestion of 50 g lactose.
RESULTS: Thirty-seven subjects had a CC genotype of the -13910 T>C polymorphism suggesting lactase non-persistence; 36 (97%) had also a positive H2 test. Eighty-six subjects had either a TC or a TT genotype suggestive of lactase persistence. Seventy-four (86%) of these tested negative on the H2 test, while 12 patients had a positive H2 test. In eight of these 12 patients duodenal biopsies showed no evidence of small bowel disease. One patient carrying a CC genotype had a negative H2 test. In this patient the rise in serum glucose after oral lactose was normal, furthermore H2 non-excretion was also excluded.
CONCLUSIONS: An excellent correlation is observed between a CC genotype and a positive H2 test, whereas the correlation between a TC or TT genotype and a negative H2 test result is less strong. Analysis of the -13910 T/C variant can be considered a good test for predicting the presence of lactase non-persistence in a patient population with suspected lactose malabsorption.