Department of Biochemistry, Panjab University, Chandigarh, India.
Clin Chim Acta. 2011 Oct 9;412(21-22):1924-30. doi: 10.1016/j.cca.2011.06.032. Epub 2011 Jul 6.
Absorption of milk sugar (lactose) is regulated by the activity of lactase enzyme in gut wall. Intestinal lactase activity declines during childhood in majority of human populations leading to adult-type hypolactasia (primary lactose malabsorption), limiting the use of fresh milk due to lactose intolerance. Aim of this study was to correlate lactase expression and activity with C/T -13910 variant in Indian children, determine the age of onset of down-regulation of lactase activity and assess the applicability of the C/T -13910 variant as a diagnostic marker for identifying children genetically inclined to develop adult-type hypolactasia.
Intestinal biopsies were obtained from 176 children aged 1-16 years undergoing routine endoscopy for various abdominal complaints. The biopsies were assayed for lactase, sucrase and maltase activities and genotyped for C/T 13910 variant using PCR-RFLP analysis. The functional effect of the C/T -13910 variant on expression of lactase mRNA and protein in these children was examined using reverse-transcription PCR and western blotting.
Among the 176 children investigated in our study, 56.8% (100/176) carried the C/C -13910 genotype, which has been associated with the onset of adult-type hypolactasia, while 40.9% (72/176) carried the C/T -13910 genotype and 2.3% (4/176) the T/T -13910 genotype. There was a significant correlation between lactase activity and C/T -13910 variant (P<0.001). The mean level of lactase activity among children with C/C -13910 genotype was 15.9 U/g protein and with C/T and T/T -13910 genotypes was 30.9 U/g protein. The age of onset of down-regulation of lactase activity in children with C/C -13910 genotype was between 3 and 5 years and keeping 10 U/g protein lactase activity as cut off, adult-type hypolactasia was evident in all the individuals>8 years of age for this genotype. C/C -13910 genotype was associated with low expression of lactase mRNA and protein compared with C/T genotype. Considering lactase activity of 10 U/g protein as gold standard, predictive value of genetic test based on C/T -13910 variant for adult-type hypolactasia was 100% in children>8 years of age.
C/T -13910 cis-acting regulatory variant located ≈14 kb upstream of lactase gene (LCT) completely correlates with lactase phenotype in Indian children. The genetic testing for the C/T -13910 variant may be helpful in the diagnosis of adult-type hypolactasia in Indian children.
乳糖（乳糖）的吸收受肠壁乳糖酶活性的调节。在大多数人群中，儿童期肠道乳糖酶活性下降，导致成人型低乳糖血症（原发性乳糖吸收不良），由于乳糖不耐受，限制了新鲜牛奶的使用。本研究的目的是在印度儿童中，将乳糖酶表达和活性与 C/T -13910 变体相关联，确定乳糖酶活性下调的发病年龄，并评估 C/T -13910 变体作为识别具有发展为成人型低乳糖血症遗传倾向的儿童的诊断标志物的适用性。
对 176 名年龄在 1-16 岁的儿童进行常规内镜检查，以治疗各种腹部不适，收集这些儿童的肠道活检样本。使用 PCR-RFLP 分析测定活检样本的乳糖酶、蔗糖酶和麦芽糖酶活性，并对 C/T 13910 变体进行基因分型。使用逆转录 PCR 和 Western 印迹分析研究 C/T -13910 变体对这些儿童中乳糖酶 mRNA 和蛋白表达的功能影响。
在我们研究的 176 名儿童中，56.8%（100/176）携带与成人型低乳糖血症发病相关的 C/C -13910 基因型，而 40.9%（72/176）携带 C/T -13910 基因型和 2.3%（4/176）携带 T/T -13910 基因型。乳糖酶活性与 C/T -13910 变体之间存在显著相关性（P<0.001）。C/C -13910 基因型儿童的乳糖酶活性平均值为 15.9 U/g 蛋白，C/T 和 T/T -13910 基因型儿童的乳糖酶活性平均值为 30.9 U/g 蛋白。C/C -13910 基因型儿童的乳糖酶活性下调发病年龄在 3 至 5 岁之间，以 10 U/g 蛋白乳糖酶活性为截断值，该基因型所有>8 岁的个体均表现为成人型低乳糖血症。与 C/T 基因型相比，C/C -13910 基因型与乳糖酶 mRNA 和蛋白的低表达相关。考虑到 10 U/g 蛋白乳糖酶活性为金标准，基于 C/T -13910 变体的遗传检测对>8 岁儿童成人型低乳糖血症的预测值为 100%。
位于乳糖酶基因（LCT）上游 ≈14 kb 的 C/T -13910 顺式作用调节变体与印度儿童的乳糖酶表型完全相关。C/T -13910 变体的基因检测可能有助于印度儿童成人型低乳糖血症的诊断。
