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. 2003 May;52(5):647-52.
doi: 10.1136/gut.52.5.647.

Transcriptional regulation of the lactase-phlorizin hydrolase gene by polymorphisms associated with adult-type hypolactasia

M Kuokkanen  1 , N S Enattah, A Oksanen, E Savilahti, A Orpana, I Järvelä
Affiliations

Transcriptional regulation of the lactase-phlorizin hydrolase gene by polymorphisms associated with adult-type hypolactasia

M Kuokkanen et al. Gut. 2003 May.

Abstract

Background and aims: The mechanism of the developmental downregulation of the lactase-phlorizin hydrolase (LPH) gene underlying adult-type hypolactasia is unknown. We have determined the functional significance of the recently identified two single nucleotide polymorphisms (SNPs), C/T(-13910) and G/A(-22018), associated with adult-type hypolactasia by studying LPH mRNA levels in intestinal biopsy samples with different genotypes.

Methods: Intestinal biopsy samples were taken from 52 patients with abdominal complaints. Hypolactasia was diagnosed by determining lactase and sucrase activities and calculating their ratio (L/S ratio). The functional effect of the C/T(-13910) and G/A(-22018) genotype on expression of LPH mRNA was demonstrated in patients heterozygous for the C/T(-13910) and G/A(-22018) polymorphism and an informative expressed SNP located in the coding region of the LPH mRNA. Reverse transcription-polymerase chain reaction followed by solid phase minisequencing was used for accessing the relative expression levels of the LPH alleles using informative SNPs located in exons 1, 2, 6, 10, 13, or 17 as markers.

Results: Statistically significant differences between the three different genotypes CC(-13910) GG(-22018), CT(-13910) GA(-22018), and TT(-13910) AA(-22018) and their respective L/S ratios were observed. Relative quantitation of the expressed LPH alleles showed that the persistent allele represented 92 (6)% (mean (SEM), range 78-99%; n=14) of the expressed LPH mRNA. The patient with the homozygous persistent TT(-13910) AA(-22018), as well as hypolactasic patients with CC(-13910) GG(-22018), showed equal expression of both alleles (47 (1)%; n=7).

Conclusions: Expression of LPH mRNA in the intestinal mucosa in individuals with T(-13910) A(-22018) alleles is several times higher than that found in individuals with C(-13910), G(-22018) alleles. These findings suggest that the two SNPs, C/T(-13910) and G/A(-22018), associated with adult-type hypolactasia, are associated with the transcriptional regulation of the LPH gene. The presence of the T(-13910) A(-22018) allele also shows significant elevation of the L/S ratio.

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Figures

Figure 1
Figure 1
The principle of quantitation of mRNA levels by solid phase minisequencing. RT-PCR, reverse transcription-polymerase chain reaction.
Figure 2
Figure 2
Standard curve constructed for determination of the amount of expressed alleles (%) using solid phase minisequencing. The amount of A+593 allele in total RNA is plotted as a function of the AG+593 ratio on a log scale.
Figure 3
Figure 3
Ratio of lactase/sucrase (L/S) activities versus genotype of each individual.
Figure 4
Figure 4
Expression levels of the lactase-phlorizin hydrolase gene between hypolactasic and heterozygous persistent individuals could be distinguished from each other—for example, exon 1 (allelic ratio on log scale versus genotype).
See this image and copyright information in PMC

Comment in

  • Changing genes; losing lactase.
    Grand RJ, Montgomery RK, Chitkara DK, Hirschhorn JN. Grand RJ, et al. Gut. 2003 May;52(5):617-9. doi: 10.1136/gut.52.5.617. Gut. 2003. PMID: 12692040 Free PMC article. No abstract available.

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