Correlation of G/A -22018 single-nucleotide polymorphism with lactase activity and its usefulness in improving the diagnosis of adult-type hypolactasia among North Indian children

Abstract

Adult-type hypolactasia (AtH or lactase non-persistence) is the physiological decline in lactase activity that manifests in majority of the world's population after weaning. Recently, various single-nucleotide polymorphisms (SNPs) upstream of lactase gene (LCT) have been suggested to be associated with AtH or the lactase persistent trait in different human populations. C/T -13910 SNP was found be completely associated with AtH in Finnish population, and G/A -22018 SNP was found to be strongly, but not completely, associated with AtH. The aim of this study was to correlate G/A -22018 SNP with intestinal lactase activity in North Indian children. These children were also genotyped for C/T -13910 SNP. We also examined the differences in milk consumption and milk-related clinical symptoms in children with different genotypes of G/A -22018 and C/T -13910 SNPs. Intestinal biopsies were obtained from 231 children aged 2-16 years undergoing routine endoscopy for various abdominal complaints. The biopsies were assayed for lactase, sucrase, and maltase activities and genotyped for G/A -22018 and C/T -13910 SNPs using restriction fragment length polymorphism and DNA sequencing analysis. There was a significant correlation between lactase activity and different genotypes of G/A -22018 SNP. Children with G/G -22018 genotype had low lactase activity. With a reference value of <10 U/g protein (lactase activity) to be indicative of AtH, the sensitivity and specificity of genetic test based on G/A -22018 SNP was 94.4 and 94.1 %, respectively. Furthermore, the consumption of milk was lower in children with G/G -22018 genotype. Flatulence was the only symptom significantly more frequent among the children with G/G -22018 genotype compared to those with G/A and A/A -22018 genotypes. However, most of the children with G/G -22018 genotype seem to tolerate small amounts of milk without any significant difference in gastrointestinal symptoms from those with G/A and A/A -22018 genotypes.

Fig. 1

Genotyping of individuals for C/T -13910 and G/A -22018 single-nucleotide polymorphisms by restriction digestion with BsmF1 and HhaΙ. Lane M DNA molecular weight marker (100 bp, Banglore Genei, India). Lane U Undigested PCR product. C/C, C/T, and T/T represent individuals with respective genotypes at -13910 position. G/G, G/A, and A/A represent individuals with respective genotypes at -22018 position