Genotyping of the lactase-phlorizin hydrolase-13910 polymorphism by LightCycler PCR and implications for the diagnosis of lactose intolerance

Background: Hypolactasia and lactose intolerance are common conditions worldwide. Hypolactasia seems to be strongly correlated with genotype C/C of the genetic variant C -> T-13910 upstream of the lactase phlorizin hydrolase (LPFD) gene. We developed a rapid genotyping assay for LPH C -> T-13910 and investigated the relationship of positive lactose breath hydrogen test (LBHT) results suggesting lactose intolerance with LPH C -> T-13910 genotype. Methods: Using automated DNA purification on the MagNA Pure LC and real-time PCR on the Light-Cycler, we examined samples from 220 individuals to estimate genotype frequencies; we then determined LPH C -> T-13910 genotype in samples from 54 Caucasian patients with a positive LBHT result and symptoms of lactose intolerance. Results: Genotyping of 220 individuals revealed frequencies of 21.4%, 41.81%, and 36.89% for genotypes C/C, C/T, and T/T. Of the patients with positive LBHT results, only 50% had the C/C genotype suggestive of primary adult hypolactasia in our study population. The other patients had various degrees of secondary hypolactasia or symptoms of lactose intolerance. Patients with C/C genotype had a mean (SD) peak H-2 increase in the LBHT [108 (58) ppm] that was significantly higher than in patients with the C/T [65 (54) ppm] and T/T [44 (34) ppm] genotypes. Conclusions: The new real-time PCR assay provides a rapid, labor-saving means for the gencityping of LPH C -> T-13910. Use of the assay may assist in differentiating patients with primary hypolactasia from those with secondary hypolactasia and lactose intolerance, who may need further clinical examinations to diagnose their underlying primary diseases. (c) 2006 American Association for Clinical Chemistry.