Effect of C/T -13910 cis-acting regulatory variant on expression and activity of lactase in Indian children and its implication for early genetic screening of adult-type hypolactasia

New insights into the molecular basis of lactase non-persistence/persistence: a brief review

Lactose, a disaccharide and main carbohydrate in milk, requires hydrolysis in the intestinal tract to release its monosaccharides galactose and glucose for use as energy source by enterocytes. This hydrolysis is catalyzed by the enzyme lactase, a β-galactosidase located in the brush border membrane of small intestinal enterocytes. In most mammals, lactase activity declines after the weaning, a condition known as lactase non-persistence (LNP). Lactase persistence (LP) is an autosomal dominant trait enabling the continued production of the enzyme lactase throughout adult life. Non-persistence or persistence of lactase expression into adult life being a polymorphic trait has been attributed to various single nucleotide polymorphisms in the enhancer region surrounding lactase gene (LCT). However, latest research has pointed to 'genetic-epigenetic interactions' as key to regulation of lactase expression. LNP and LP DNA haplotypes have demonstrated markedly different epigenetic aging as genetic factors contribute to gradual accumulation of epigenetic changes with age to affect lactase expression. This review will attempt to present an overview of latest insights into molecular basis of LNP/LP including the crucial role of 'genetic-epigenetic interactions' in regulating lactase expression.

Lactase Non-persistence and Lactose Intolerance

PURPOSE OF REVIEW

To evaluate the clinical and nutritional significance of genetically determined lactase non-persistence and potential lactose and milk intolerance in 65-70% of the world's adult population.

RECENT FINDINGS

Milk consumption is decreasing in the USA and is the lowest in countries with a high prevalence of lactase non-persistence. The dairy industry and Minnesota investigators have made efforts to minimize the influence of lactose intolerance on milk consumption. Some lactose intolerant individuals, without co-existent irritable bowel syndrome, are able to consume a glass of milk with a meal with no or minor symptoms. The high frequency of lactase persistence in offspring of Northern European countries and in some nomadic African tribes is due to mutations in the promoter of the lactase gene in association with survival advantage of milk drinking. Educational and commercial efforts to improve calcium and Vitamin D intake have focused on urging consumption of tolerable amounts of milk with a meal, use of lowered lactose-content foods including hard cheeses, yogurt, and lactose-hydrolyzed milk products.

A study of the molecular variants associated with lactase persistence in different Ecuadorian ethnic groups

OBJECTIVE

Lactase persistence (LP) is an adaptive trait that certain human populations have acquired in response to lactose consumption in adulthood. The T-13910 variant has been reported as a causal polymorphism in Europeans. The Ecuadorian population has been described as multicultural and multiethnic, comprised of three main ethnic groups (Mestizo, Native Amerindian, and Afro-Ecuadorian). The aim of the study was to identify the molecular basis of LP in these admixed populations for the first time and determine the association between the T-13910 marker and the European ancestry proportion of each ethnic group.

METHODS

Genotyping was performed in 741 Ecuadorian individuals by sequencing a 576 bp region around the -13910 position upstream of the LCT gene. The ancestry proportions of Mestizo, Afro-Ecuadorian, and Native Amerindians were calculated using Ancestry Informative Markers and were compared with the diversity panel of the Human Genome Diversity Project.

RESULTS

LP prevalence calculated from T-13910 allele frequency in Mestizo, Afro-Ecuadorian, and Native Amerindians was 24.4%, 16%, and 12.5%, respectively. The ancestry percentage correlated to the admixture proportion of each ethnic group, and the C/T-13910 genotype frequency was influenced by the European ancestry proportion.

CONCLUSIONS

The presence of the T-13910 polymorphism in the Ecuadorian population suggested that LP was a trait introduced by European migration and inherited by admixture that occurred during the colonization of South America. This variant was not fixed in a population with a history of admixture, and its allele frequency was proportional to the ancestry proportion of each Ecuadorian ethnic group. Am. J. Hum. Biol. 28:774-781, 2016. © 2016Wiley Periodicals, Inc.

A prospective study comparing histology and enteric enzyme function of patients with extrahepatic portal vein obstruction before and after shunt surgery

BACKGROUND

This was a prospective observational study carried out to objectively assess the effect of shunt surgery on intestinal morphology and function in patients with extrahepatic portal vein obstruction (EHPVO) and correlate it with growth improvement.

PATIENTS AND METHODS

Twenty patients who were operated upon for EHPVO were divided into two groups for the purpose of analysis depending on the outcome of surgery: group A--patients who underwent successful shunt surgery (n=14) and group B--patients who underwent splenectomy with devascularization (n=1) and those with thrombosed shunts (n=5). The patient groups were created on the basis of the type and outcome of the surgery and not prospective stratification. Growth parameters, endoscopy findings, duodenal histology, brush border enzyme activity, urinary D-xylose levels, fecal steatocrit, fecal α-1 antitrypsin, serum growth hormone and insulin-like growth factor-1 levels, and quality-of-life scores were assessed before surgery and at a mean of 24.9 weeks after surgery.

RESULTS

There was no significant difference between the preoperative and postoperative duodenal histology. Preoperative brush border lactase activity was significantly lower than normal and did not change significantly after surgery. EHPVO did not affect intestinal absorption or permeability. Shunt surgery resulted in significantly improved z scores for height after surgery as well as quality of life. There was no significant growth hormone resistance.

CONCLUSION

Our patients did not have any significant malabsorption or abnormality in small intestinal structure and function when compared with established normal levels. There was no significant change in the above parameters after shunt surgery, although an improvement in growth was observed. Thus, factors other than enteropathy or other lesser known enteral factors seem to be responsible for the growth retardation observed in EHPVO and its subsequent improvement after shunt surgery.

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

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.