A re-appraisal of lactose intolerance

Background: Lactose, β‐galactose‐1,4‐glucose, is hydrolysed by the enzyme lactase. Lactose intolerance occurs when lactase deficiency causes clinical symptoms. Aims: To provide an overview of lactose intolerance, including definition, aetiology and epidemiology, the clinical symptoms and diagnostic testing and management. Methods: A literature review was carried out to meet the aims of this paper. This resulted in the analysis of a database of patients tested for lactose intolerance to provide examples of the consequences of problems of terminology identified. Conclusions: The terminology relating to lactose intolerance is confusing for clinicians and researchers. Clinicians need to ensure that these problematic terms do not cause diagnostic mistakes and inappropriate treatment. Researchers should be aware of inconsistent terminology in studies and resultant problems with the interpretation of results.     

The biosynthetic basis of adult lactase deficiency.

The intestinal brush-border enzyme lactase splits lactose into its component monosaccharides, glucose and galactose. Relative deficiency of the enzyme during adulthood is a common condition worldwide and is frequently associated with symptoms of lactose intolerance. We studied the synthesis and processing of lactase in normal and adult hypolactasic subjects using human intestinal explants in organ culture. Metabolic labeling experiments in our control subjects with [35S]methionine followed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, and fluorography demonstrated that newly synthesized lactase is initially recognized as a precursor molecule with a relative molecular weight (Mr) of 205,000. Over the course of several hours most of the labeled lactase was converted to a mature form of 150,000 Mr. Transiently appearing forms of 215,000 and 190,000 Mr were identified and were felt to represent intermediary species generated during intracellular processing. We identified two distinct alterations in lactase biosynthesis accounting for adult hypolactasia. Studies in three deficient subjects demonstrated markedly reduced synthesis of the precursor protein though posttranslational processing appeared identical to normal. Multiple studies in a fourth deficient subject demonstrated synthesis of ample amounts of precursor lactase but reduced conversion to the mature active form of the enzyme.     

Selected disorders of malabsorption

Malabsorption syndrome encompasses numerous clinical entities that result in chronic diarrhea, abdominal distention, and failure to thrive. These disorders may be congenital or acquired and include cystic fibrosis and Shwachman-Diamond syndrome; the rare congenital lactase deficiency; glucose-galactose malabsorption; sucrase-isomaltase deficiency; adult-type hypolactasia leading to acquired lactose intolerance. The pathology may be due to impairment in absorption or digestion of nutrients resulting in Nutritional deficiency, gastrointestinal symptoms, and extra gastrointestinal symptoms. Treatment is aimed at correcting the deficiencies and symptoms to improve quality of life. Common disorders of malabsorption celiac disease, pernicious anemia, and lactase deficiency are discussed in this article.     

High-resolution melting analysis using unlabeled probe and amplicon scanning simultaneously detects several lactase persistence variants

Lactase persistence and thereby tolerance to lactose is a common trait in people of Northern European descent. It is linked to the LCT -13910C>T variant located in intron 13 of the MCM6 gene 13.9 kb upstream of the lactase (LCT) gene. In people of African and Middle Eastern descent, lactase persistence can be associated with other variants nearby the -13910C>T variant, limiting the use of the -13910C>T-based SNP analysis, e.g. TaqMan assays for the diagnosis of lactose intolerance. Using high-resolution melting analysis, we identified five samples that were heterozygous for the -13915T>G variant among 78 patients genotyped as -13910C/C by a TaqMan assay. All samples originated from patients of probable Middle Eastern descent. In order to detect the -13910 and -13915 variants simultaneously, we developed a new high-resolution melting (HRM) analysis assay based on unlabeled probe genotyping and simultaneous amplicon scanning analysis. By using this assay we were able to distinguish the -13910 and -13915 genotypes clearly. Furthermore, we identified two rare variants, the -13907C>G and -13913T>C. With this method, based on an inexpensive unlabeled probe, it is possible to simultaneously detect the -13910C>T and -13915T>G variants in addition to rarer variants surrounding the -13910 site. This new method may contribute to improve the diagnostic performance of the genetic analysis for lactose intolerance.     

Selective alteration of brush-border hydrolases in intestinal diseases in childhood

1. Biochemical estimates of lactase, sucrase and maltase activities, carried out on intestinal biopsies appearing histologically normal, were compared with those obtained from children suffering from coeliac disease, cow's milk protein intolerance/postenteritis syndrome and the intractable diarrhoea syndrome of infancy. Lactase deficiency in these children was found to be more pronounced than sucrase or maltase deficiencies. 2. Quantitative cytochemical investigations showed characteristic disease-induced changes in the ability of enterocytes to express alpha- and beta-glucosidases, but not alkaline phosphatase activities, during migration along stunted villi. 3. Separate estimates of the time course describing hydrolase development in normal and coeliac tissue showed the initial rate of lactase appearance to be halved in coeliac patients, while that for alpha-glucosidases remained constant and that for alkaline phosphatase increased by a factor of four. Enteroblastic replacement of mature enterocytes cannot provide a general explanation for hydrolase deficiency in diseased intestine.     

Lactose intolerance. Pinpointing the source of nonspecific gastrointestinal symptoms

Lactose intolerance is a common condition that can cause nonspecific gastrointestinal symptoms. A reliable diagnosis cannot be made on the basis of the patient's history. The breath hydrogen test is simple, noninvasive, accurate, and inexpensive and is the diagnostic method of choice. In addition to traditional dietary restriction of lactose, treatment may consist of alterations in dietary fat content or caloric density to reduce symptoms and use of dairy products or additives that provide lactase activity.     

婴儿原发性乳糖不耐受症的临床诊断与治疗

目的 探讨婴儿原发性乳糖不耐受症的临床特征和诊治方法.方法 对我院消化科门诊2009年10月至201 1年2月诊断为原发性乳糖不耐受症婴儿的临床资料进行分析.结果 26例患儿均生后1～2个月内发病,病程1～4个月;母乳喂养10例,混合喂养8例,奶粉喂养8例.临床表现为慢性或迁延性腹泻,大便稀水样或泡沫状,每天4～8次;19例曾接受抗生素治疗无好转.经去乳糖饮食及口服益生菌均于1周症状好转,再次食用乳类临床症状复发.结论 婴儿原发性乳糖不耐受症主要表现为长期腹泻,易误诊并滥用抗生素,去乳糖饮食有助于确诊并治疗本病.     

High-resolution melting analysis using unlabeled probe and amplicon scanning simultaneously detects several lactase persistence variants

Abstract

Lactase persistence and thereby tolerance to lactose is a common trait in people of Northern European descent. It is linked to the LCT ?13910C>T variant located in intron 13 of the MCM6 gene 13.9 kb upstream of the lactase (LCT) gene. In people of African and Middle Eastern descent, lactase persistence can be associated with other variants nearby the ?13910C>T variant, limiting the use of the ?13910C>T-based SNP analysis, e.g. TaqMan assays for the diagnosis of lactose intolerance. Using high-resolution melting analysis, we identified five samples that were heterozygous for the ?13915T>G variant among 78 patients genotyped as ?13910C/C by a TaqMan assay. All samples originated from patients of probable Middle Eastern descent. In order to detect the ?13910 and ?13915 variants simultaneously, we developed a new high-resolution melting (HRM) analysis assay based on unlabeled probe genotyping and simultaneous amplicon scanning analysis. By using this assay we were able to distinguish the ?13910 and ?13915 genotypes clearly. Furthermore, we identified two rare variants, the ?13907C>G and ?13913T>C. With this method, based on an inexpensive unlabeled probe, it is possible to simultaneously detect the ?13910C>T and ?13915T>G variants in addition to rarer variants surrounding the ?13910 site. This new method may contribute to improve the diagnostic performance of the genetic analysis for lactose intolerance.     

Intestinal β-galactosidases: II. Biochemical alteration in human lactase deficiency

Despite the high prevalence of intestinal lactase deficiency in some racial groups and in patients with intestinal disease, the biochemical defect has not been characterized.In the preceding paper normal intestine was found to have two lactases with distinctly different pH optima. Therefore, pH activity curves of homogenates from lactase-deficient intestine were studied, and the pH optimum was found to be shifted from the normal of 5.8 to 4.8. Density gradient ultracentrifugation of intestinal material from five lactase-deficient patients demonstrated absence of a lactase with pH optimum 6.0 and molecular weight 280,000. A second lactase with pH optimum 4.5 and molecular weights of 156,000 and 660,000 remained at normal levels accounting for the shift in the pH optimum in whole intestinal homogenates. In addition, three of the five patients had absence of a smaller beta-galactosidase (molecular weight 80,000) that had specificity only for synthetic substrates. Although not a lactase, this enzyme had a pH optimum identical with the missing lactase, and its activity was inhibited by lactose in a partially competitive manner suggesting that it is capable of binding lactose. It is possible that this enzyme is a precursor or fragment of the missing lactase.The residual lactase activity provided by the lactase with low pH optimum represents 20-70% of the activity of the missing enzyme, and yet these patients are not able to digest dietary lactose. Thus it appears that the residual enzyme plays no significant role in the hydrolysis of ingested lactose.     

Frequent causes of diarrhea: celiac disease and lactose intolerance

Celiac disease and lactose intolerance are both relatively frequent diseases with symptoms occurring after ingestion of certain food components.In celiac disease wheat gluten and related proteins of other cereals induce an inflammatory disease of the small intestine in predisposed individuals, leading to gastrointestinal and extraintestinal symptoms. Moreover, there is an association with many other diseases and besides classic symptoms (diarrhea, weight loss, malabsorption) atypical courses with less or lacking gastrointestinal symptoms exist. The prevalence is about 1 : 100 (Europe, USA) and higher than supposed earlier. Diagnostic criteria include serologic tests (tissue transglutaminase antibody, endomysial antibody) and characteristic small bowel histology (lymphocytic infiltration, villous atrophy). Therapy is a strict and lifelong gluten-free diet. Rarely, refractory disease or lack of compliance are associated with increased risk of malignancy and worse prognosis.Lactose intolerance is attributed to low intestinal lactase levels, due to reduced genetic expression or mucosal injury and consequent intolerance to dairy products. The frequency is varying in different ethnic groups, occurring in 10-15% of Northern European people. Intensity of clinical symptoms (diarrhea, abdominal pain, bloating) depends on the amount of ingested lactose and individual activity of intestinal lactase. The capacity of lactose malabsorption can be measured using the noninvasive lactose breath hydrogen test. The treatment is based on a reduced dietary lactose intake or in case of secondary form treatment of the underlying disease.     

Some new and important clues to the causes of colic

Colic, or persistent unexplained crying in infants, is commonly encountered by health professionals. While not harmful to the child, it can place a great deal of stress on the parents and family. The cause of colic has not been definitively identified. Transient lactose intolerance, as a result of inadequate production of the enzyme lactase, is one possibility. Studies have shown a reduced crying time when formula or breast milk is incubated with lactase. Colief Infant Drops consist of lactase in a glycerol and water solution which, when added to formula or breast milk, converts lactose to simple sugars and makes the feed more easily digestible.     

Hydrogen breath testing versus LCT genotyping for the diagnosis of lactose intolerance: a matter of age?

BACKGROUND: Two single nucleotide polymorphisms (-13910 C/T and -22018 G/A) upstream of the lactase gene (LCT) have been found to be associated with lactose tolerance in Europeans. METHODS: In one hundred and twenty Austrian outpatients, who visited the physician's office for symptoms of irritable bowel syndrome (IBS), hydrogen breath testing (HBT) and LCT genotyping by polymerase chain reaction and reverse-hybridisation were performed in parallel. RESULTS: The coincidence between a genotype suggesting lactase non-persistence (lactose intolerance) and a positive HBT result was almost perfect (97.4% for LCT-13910 C/T and 100% for LCT-22018 G/A). Between a genotype indicating lactase persistence (lactose tolerance) and a negative HBT result the coincidence was lower (72% and 71.4%, respectively). Among heterozygotes, there was a statistically significant increase in the proportion of positive HBT results with age. Both SNPs were in accordance in 117/120 (97.5%) patients. CONCLUSION: Genetic analysis of LCT-13910 C/T and LCT-22018 G/A is a good indicator for the presence of lactose intolerance. Because age, as well as a number of secondary causes (e.g. celiac disease), can influence HBT results, it is useful to combine HBT and genetic analysis in the diagnostic assessment of IBS.     

Genotyping of the lactase-phlorizin hydrolase -13910 polymorphism by LightCycler PCR and implications for the diagnosis of lactose intolerance

BACKGROUND: Hypolactasia and lactose intolerance are common conditions worldwide. Hypolactasia seems to be strongly correlated with genotype C/C of the genetic variant C-->T(-13910) upstream of the lactase phlorizin hydrolase (LPH) gene. We developed a rapid genotyping assay for LPH C-->T(-13910) and investigated the relationship of positive lactose breath hydrogen test (LBHT) results suggesting lactose intolerance with LPH C-->T(-13910) genotype. METHODS: Using automated DNA purification on the MagNA Pure LC and real-time PCR on the LightCycler, we examined samples from 220 individuals to estimate genotype frequencies; we then determined LPH C-->T(-13910) genotype in samples from 54 Caucasian patients with a positive LBHT result and symptoms of lactose intolerance. RESULTS: Genotyping of 220 individuals revealed frequencies of 21.4%, 41.8%, and 36.8% for genotypes C/C, C/T, and T/T. Of the patients with positive LBHT results, only 50% had the C/C genotype suggestive of primary adult hypolactasia in our study population. The other patients had various degrees of secondary hypolactasia or symptoms of lactose intolerance. Patients with C/C genotype had a mean (SD) peak H2 increase in the LBHT [108 (58) ppm] that was significantly higher than in patients with the C/T [65 (54) ppm] and T/T [44 (34) ppm] genotypes. CONCLUSIONS: The new real-time PCR assay provides a rapid, labor-saving means for the genotyping of LPH C-->T(-13910). Use of the assay may assist in differentiating patients with primary hypolactasia from those with secondary hypolactasia and lactose intolerance, who may need further clinical examinations to diagnose their underlying primary diseases.     

Noninvasive evaluation of intestinal lactase with 4-galactosylxylose: comparison with 3- and 2-galactosylxylose and optimization of the method in rats

BACKGROUND: Urinary excretion of D-xylose by suckling rats after ingestion of a mixture of 4-, 3-, and 2-galactosylxyloses reflects lactase activity in vivo. We aimed to select the most convenient of these disaccharides for detecting changes of the enzyme activity in vivo and to optimize the method. METHODS: 4-, 3-, and 2-galactosylxyloses were synthesized and purified, then orally administered to suckling rats of different ages. D-Xylose was measured colorimetrically by the phloroglucinol reaction in urine and plasma. Lactase activity was determined in extracts of small intestine mucosa with lactose, galactosylxyloses, and phlorizin as substrates. RESULTS: D-Xylose appeared in the urine in a dose-dependent manner after ingestion of any of the 3 galactosylxylose disaccharides. Correlation between D-xylose elimination and intestinal lactase activity was highest with 4-galactosylxylose (r = 0.97; n = 24), lower with 2-galactosylxylose (r = 0.89; n = 24), and lowest with 3-galactosylxylose (r = 0.34; n = 23). The kinetic properties of intestinal lactase accounted for these differences. D-Xylose concentration in plasma after administration of 4-galactosylxylose also correlated with lactase activity (r = 0.93; n = 33). CONCLUSIONS: 4-Galactosylxylose is the most suitable compound for the evaluation of lactase activity in vivo. Measurement of the derived D-xylose in either urine or blood gives an estimate of the total lactose digestive capacity of the small intestine. The optimized method holds promise for development of a simple, low-cost, and reliable new test for the noninvasive diagnosis of hypolactasia.     

Patients with functional bowel disorder have disaccharidase deficiency: A single-center study from Russia

BACKGROUNDFunctional bowel disorder (FBD) may be caused by a decrease in disaccharidase activity. Thus, the timely diagnosis of disaccharidase deficiency could lead to a better prognosis in patients with this condition.AIMTo determine the potential value of intestinal disaccharidases glucoamylase, maltase, sucrase, and lactase in understanding the etiology and pathogenesis of FBD.METHODSA total of 82 FBD patients were examined. According to the Rome IV criteria (2016), 23 patients had diarrhea-predominant irritable bowel syndrome (IBS), 33 had functional diarrhea, 10 had constipation-predominant IBS, 4 had functional constipation, and 12 had mixed IBS. The Dahlqvist method was used to measure disaccharidase activity in the brush-border membrane of mature enterocytes of the small intestine, in duodenal biopsies obtained during esophagogastroduodenoscopy.RESULTSLactase deficiency was detected in 86.5% of patients, maltase deficiency in 48.7%, sucrase deficiency in 50%, and glucoamylase deficiency in 84.1%. The activities of all enzymes were reduced in 31.7% of patients, and carbohydrase deficiency was detected in 63.5% of patients. The low activity of enzymes involved in membrane digestion in the small intestine was found in 95.2% of patients.CONCLUSIONIn 78 of the 82 patients with FBD, gastrointestinal symptoms were associated with disaccharidase deficiency.     

Lactose intolerance: analysis of underlying factors

BACKGROUND: We studied the degree of lactose digestion and orocecal transit time (OCTT) as possible causes for the variability of symptoms of lactose intolerance (LI) in a sample of a population with genetically determined low lactase activity. METHODS: Lactose digestion index (LDI) was measured by the recently developed 13C-lactose/2H-glucose test. The OCTT was determined using the breath hydrogen test. Based on a 6-h symptom score (SSC) after a challenge dose of 25 g of lactose the subjects were divided into a tolerant group (T: n= 15; SSC = 0) and an intolerant group (IT: n= 28; SSC 1-40). The intolerant group was subdivided according to the severity of symptoms: group ITa (n = 17; mild symptoms without diarrhoea) and group ITb (n = 11; with diarrhoea). RESULTS: The LDI was lower in the intolerant group (0.34 +/- 0.14) (mean +/- SD) than in the tolerant group (0.47 +/- 0.14) (P = 0.008). The OCTT of group IT (60, 30-90 min) (median, quartiles) was significantly shorter than that of group T (105, 60-120 min) (P = 0.003) and was positively correlated with the LDI (P = 0.050). In groups ITa and ITb the OCTT (60, 30-90 min; 60, 26-83 min) and LDI (0.30 +/- 0.14; 0.39 +/- 0.14) were similar. CONCLUSIONS: Lactose digestion capacity, which is determined by small intestinal lactase activity as well as by OCTT, affects the occurrence of lactose intolerance. However, the major difference in intolerance symptoms is caused by differences in the colonic processing of maldigested lactose.     

13CO2 breath test using naturally 13C-enriched lactose for detection of lactase deficiency in patients with gastrointestinal symptoms

A 13CO2 breath test using naturally enriched 13C-lactose as a substrate was performed in 47 patients with chronic abdominal pain or chronic diarrhea, taken from a population with a low prevalence of primary acquired lactase deficiency. The cumulative 13CO2 excretion 4 hours after 13C-lactose intake was compared with the H2 breath excretion and with jejunal lactase activity. A physiologically significant relation was found between the cumulative 13CO2 excretion (at 4 hours) and lactase activity, 14.5% 13CO2 excretion being the best cutoff point for discrimination between patients with low and normal lactase activity. The 13CO2 breath test was found to be more sensitive (0.84 versus 0.68) and more specific (0.96 versus 0.89) than the H2 breath test in detecting low jejunal lactase activity. Concordant results of both breath tests performed simultaneously give a reliable picture of the lactose absorption status of the patient. Discordance in results of 13CO2 and H2 lactose breath tests, if not explained by history, indicates in which patients a jejunal biopsy should be performed. If lactase activity and morphology of the biopsy are normal, other causes of discordance must be investigated.     

食物不耐受血清特异性IgG抗体检测在临床中的应用

目的 探讨血清中14种食物不耐受特异性IgG抗体与临床疾病的关系,为临床提供诊治相关疾病的依据.方法 应用酶联免疫法检测110例临床常见慢性疾病患者及30例健康人血清中食物特异性IgG水平.结果 人群中食物不耐受特异性IgG升高均有1～8种不等,总阳性率为100%,顺序为:牛奶＞小麦＞螃蟹＞鸡蛋＞虾米＞鳕鱼＞大豆＞牛肉＞猪肉＞大米＞鸡肉＞玉米＞蘑菇＞番茄.根据试验结果调整所有患者的饮食,患者症状多可以明显改善.结论 测定食物不耐受特异性IgG抗体,并尽早将阳性食物从患者食谱中去除,在临床疾病诊治中有重要意义.     

Wide variations in the testing of lactose tolerance: results of a questionnaire study in Finnish health care centres

About 70% of the world's adult population is unable to digest lactose, the sugar found naturally only in milk. This disability leads to gastrointestinal symptoms called lactose intolerance. In Finland, many patients visit health care centres because they are suffering from gastrointestinal symptoms. A few of them are diagnosed as being lactose intolerant. However, a far larger number diagnose themselves as suffering from lactose intolerance. Therefore the diagnostic tests used should be carefully validated and standardized in clinical laboratories throughout the country. The aim of this questionnaire study was to clarify the situation centres with adult patients in Finnish health care and to try to standardize procedures for administering lactose tolerance tests.     

Wide variations in the testing of lactose tolerance: results of a questionnaire study in Finnish health care centres

About 70% of the world's adult population is unable to digest lactose, the sugar found naturally only in milk. This disability leads to gastrointestinal symptoms called lactose intolerance. In Finland, many patients visit health care centres because they are suffering from gastrointestinal symptoms. A few of them are diagnosed as being lactose intolerant. However, a far larger number diagnose themselves as suffering from lactose intolerance. Therefore the diagnostic tests used should be carefully validated and standardized in clinical laboratories throughout the country. The aim of this questionnaire study was to clarify the situation centres with adult patients in Finnish health care and to try to standardize procedures for administering lactose tolerance tests.