title: Lactase persistence versus decline in human adults: multifactorial events are involved in down-regulation after weaning.
abstract: OBJECTIVE
  In nonhuman mammals, lactase activity declines during or after weaning. In contrast, about one half of the human species maintains high lactase activity even in adulthood. To clarify this difference, this study examined some parameters for which contrasting observations have been reported in connection with lactase decline.
  
  
  METHODS
  Lactase activity, lactase messenger RNA (mRNA) levels, and in vitro lactase biosynthesis were determined in normal jejunal samples from a large group of white adults, all born in or near Naples.
  
  
  RESULTS
  Of 44 individuals, 10 were lactase persistent and 34 were hypolactasic. Biosynthesis of prolactase correlated well with lactase mRNA levels, indicating transcriptional control; it did less so with steady-state lactase activity. Examination of lactase mRNA levels and lactase activity/lactase mRNA ratios revealed a heterogeneous pattern of lactase mRNA level, lactase synthesis, and activity in both lactase persistent and hypolactasic subjects.
  
  
  CONCLUSIONS
  Both transcriptional and posttranscriptional factors cause the decline of intestinal lactase. This probably explains the multifarious observations that most studies on adult-type hypolactasia have reported. The single overriding factor distinguishing lactase-persistent subjects from hypolactasic subjects is the high rate of lactase biosynthesis.
authors.affiliation: Department of Pediatrics, University Federico II, Naples, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Rossi
authors.forename: L
authors.initials: L
authors.lastname: Maiuri
authors.forename: M I
authors.initials: MI
authors.lastname: Fusco
authors.forename: V M
authors.initials: VM
authors.lastname: Salvati
authors.forename: A
authors.initials: A
authors.lastname: Fuccio
authors.forename: S
authors.initials: S
authors.lastname: Auricchio
authors.forename: N
authors.initials: N
authors.lastname: Mantei
authors.forename: L
authors.initials: L
authors.lastname: Zecca
authors.forename: S M
authors.initials: SM
authors.lastname: Gloor
authors.forename: G
authors.initials: G
authors.lastname: Semenza
mesh_terms: D000328:Adult; D000368:Aged; D046508:Culture Techniques; D005260:Female; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D010694:Lactase-Phlorizin Hydrolase / Q000235:genetics; D008297:Male; D008875:Middle Aged; D012333:RNA, Messenger / Q000378:metabolism; D014886:Weaning; D001616:beta-Galactosidase / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D001616:beta-Galactosidase; D010694:Lactase-Phlorizin Hydrolase