title: Lactase persistence versus lactose intolerance: Is there an intermediate phenotype?
abstract: BACKGROUND
  According to the prevailing theory about the genetic background to lactose intolerance, there are three genotypes but only two adult physiological phenotypes: lactase persistence in individuals with the CT and TT genotypes and lactase non-persistence in individuals with the CC genotype. However, analysis of lactase activity from intestinal biopsies has revealed three distinct levels of activity, suggesting that an intermediate physiological phenotype may exist.
  
  
  OBJECTIVE
  To assess possible disparities between different genotypes with regard to biomarkers of lactase activity and physical symptoms during an oral lactose load test.
  
  
  METHODS
  A retrospective study using an oral lactose load test (n=487). Concentrations of hydrogen in exhaled air and blood glucose were measured. Afterwards, subjects were asked to provide oral mucosa samples for genotyping and answer a questionnaire (participation rate 56%, n=274).
  
  
  RESULTS
  Mean hydrogen levels in exhaled air at 120min were significantly higher in the CT genotype than in the TT genotype. There was no significant difference in blood glucose levels between the two groups. Reported symptoms, with the possible exception of abdominal pain, were equally prevalent in both groups.
  
  
  CONCLUSIONS
  Subjects with the CT and TT genotypes, hitherto classified as lactase-persistent, differ in their physiological response to lactose intake, indicating differences in phenotype which could have clinical significance.
authors.affiliation: University Health Care Research Center, School of Health and Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden. Electronic address: zbigniew.dzialanski@regionorebrolan.se.
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Dzialanski
authors.affiliation: Department of Clinical Physiology, School of Health and Medicine Sciences, Örebro University, SE 701 82 Örebro, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Barany
authors.affiliation: University Health Care Research Center, School of Health and Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Engfeldt
authors.affiliation: Clinical Epidemiology and Biostatistics, School of Health and Medicine Sciences, Örebro University, SE 701 82 Örebro, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Magnuson
authors.affiliation: Department of Clinical Chemistry, School of Health and Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden.
authors.forename: Lovisa A
authors.initials: LA
authors.lastname: Olsson
authors.affiliation: Department of Medical Biosciences/Clinical Chemistry, Faculty of Medicine and Health, Umeå University, SE 901 87 Umeå, Sweden.
authors.forename: Torbjörn K
authors.initials: TK
authors.lastname: Nilsson
mesh_terms: D015746:Abdominal Pain / Q000201:enzymology / Q000235:genetics; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D015415:Biomarkers / Q000097:blood; D005260:Female; D005838:Genotype; D006801:Humans; D043322:Lactase / Q000235:genetics / Q000378:metabolism*; D007787:Lactose Intolerance / Q000201:enzymology / Q000235:genetics*; D007789:Lactose Tolerance Test; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D015995:Prevalence; D012189:Retrospective Studies; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D015415:Biomarkers; D043322:Lactase; D001616:beta-Galactosidase
keywords: 13910 C/T allele; Abdominal pain; Hydrogen breath test; Oral lactose load test