Lactose malabsorption in Finnish children of school age

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.

Lactose digestion in humans: intestinal lactase appears to be constitutive whereas the colonic microbiome is adaptable

Globally, ∼70% of adults are deficient in intestinal lactase, the enzyme required for the digestion of lactose. In these individuals, the consumption of lactose-containing milk and dairy products can lead to the development of various gastrointestinal (GI) symptoms. The primary solution to lactose intolerance is withdrawing lactose from the diet either by eliminating dairy products altogether or substituting lactose-free alternatives. However, studies have shown that certain individuals erroneously attribute their GI symptoms to lactose and thus prefer to consume lactose-free products. This has raised the question whether consuming lactose-free products reduces an individual's ability to absorb dietary lactose and if lactose-absorbers should thus avoid these products. This review summarizes the current knowledge regarding the acclimatization of lactose processing in humans. Human studies that have attempted to induce intestinal lactase expression with different lactose feeding protocols have consistently shown lack of enzyme induction. Similarly, withdrawing lactose from the diet does not reduce intestinal lactase expression. Evidence from cross-sectional studies shows that milk or dairy consumption is a poor indicator of lactase status, corroborating the results of intervention studies. However, in lactase-deficient individuals, lactose feeding supports the growth of lactose-digesting bacteria in the colon, which enhances colonic lactose processing and possibly results in the reduction of intolerance symptoms. This process is referred to as colonic adaptation. In conclusion, endogenous lactase expression does not depend on the presence of dietary lactose, but in susceptible individuals, dietary lactose might improve intolerance symptoms via colonic adaptation. For these individuals, lactose withdrawal results in the loss of colonic adaptation, which might lower the threshold for intolerance symptoms if lactose is reintroduced into the diet.

Genetic determinants of beverage consumption: Implications for nutrition and health

Beverages make important contributions to nutritional intake and their role in health has received much attention. This review focuses on the genetic determinants of common beverage consumption and how research in this field is contributing insight to what and how much we consume and why this genetic knowledge matters from a research and public health perspective. The earliest efforts in gene-beverage behavior mapping involved genetic linkage and candidate gene analysis but these approaches have been largely replaced by genome-wide association studies (GWAS). GWAS have identified biologically plausible loci underlying alcohol and coffee drinking behavior. No GWAS has identified variants specifically associated with consumption of tea, juice, soda, wine, beer, milk or any other common beverage. Thus far, GWAS highlight an important behavior-reward component (as opposed to taste) to beverage consumption which may serve as a potential barrier to dietary interventions. Loci identified have been used in Mendelian randomization and gene×beverage interaction analysis of disease but results have been mixed. This research is necessary as it informs the clinical relevance of SNP-beverage associations and thus genotype-based personalized nutrition, which is gaining interest in the commercial and public health sectors.

Oral Diets and Nutrition Support for Inflammatory Bowel Disease: What Is the Evidence?

Inflammatory bowel disease (IBD), which primarily includes Crohn's disease and ulcerative colitis, involves chronic inflammation of the gastrointestinal tract. The mechanisms of IBD pathogenesis are not well understood at this time, but likely involve an interaction between genetic, gut microbial, immune, and environmental factors. Emerging epidemiologic studies have suggested a relationship between specific dietary nutrients as an environmental factor and IBD risk. Clinical trials have also shown oral diets to have variable efficacy in affecting clinical outcomes for IBD. This review discusses the key studies that evaluated the use of various oral diets as well as nutrition support in the management of IBD.

The European lactase persistence genotype determines the lactase persistence state and correlates with gastrointestinal symptoms in the Hispanic and Amerindian Chilean population: a case-control and population-based study

BACKGROUND

The lactase persistent (LP) or lactase non-persistent (LNP) state in European adults is genetically determined by a single nucleotide polymorphism (SNP) located 13.9 kb upstream of the lactase (LCT) gene, known as LCT C>T(-13910) (rs4988235). The LNP condition leads to an inability to digest the milk sugar lactose leading to gastrointestinal symptoms and can affect nutrient and calcium intake in certain populations.

OBJECTIVES

The authors studied a group of 51 Chilean patients to assess whether this SNP influences the LP/LNP state in this population, and determined the prevalence of LCT C>T(-13910) genotypes in a representative sample of 216 Hispanics and 43 Amerindians with correlation to digestive symptoms.

DESIGN

Case-control study done in Chilean patients with clinical suspicion of LNP that were assessed using clinical survey, hydrogen breath test (HBT) and SNP genotyping. The population sample of Hispanics and Amerindians was assessed by clinical survey and SNP genotyping.

RESULTS

Of the 51 patients with clinical suspicion of LNP, 29 were HBT-positive. The CC genotype (LNP) was present in 89.7% of the patients with positive HBT and in only 4.7% of those with negative HBT. The prevalence of the CC genotype was 56.9% in the Hispanic population and 88.3% in Amerindians, and was associated with a higher self-reported clinical intolerance to ingestion of dairy products.

CONCLUSION

The LP/LNP state is determined by the LCT C>T(-13910) variant in Chileans. This variant predicts digestive symptoms associated with the ingestion of lactose and is a good tool for the diagnosis of primary adult hypolactasia. The LCT T(-13910) allele is rare in the Amerindian population and is suggestive of European ancestry in this contemporary population.

Adult-type hypolactasia is not a predisposing factor for the early functional and structural changes of atherosclerosis: the Cardiovascular Risk in Young Finns Study

Individuals suffering from ATH (adult-type hypolactasia), defined by the LCT (gene encoding lactase-phlorizin hydrolase) C/C(-13910) genotype (rs4988235), use less milk and dairy products and may have higher plasma HDL (high-density lipoprotein) and lower triacylglycerol (triglyceride) concentrations than their counterparts without ATH. To investigate the effects of ATH status on the early markers of atherosclerosis, we examined its association with CIMT (carotid intima-media thickness), CAC (carotid artery compliance) and brachial artery FMD (flow-mediated dilation) in a young population-based cohort of otherwise healthy individuals. As part of the Cardiovascular Risk in Young Finns Study, we performed CIMT, CAC and FMD analyses, LCT C/T(-13910) genotyping and risk factor determination in 2109 young subjects 24-39 years of age (45% males) at the time of the examination. The consumption of both milk and dairy products was lowest and the consumption of alcohol highest in subjects with the C/C(-13910) genotype (P<0.001 for all) in comparison with subjects without ATH (TT+CT). In multivariate analysis, no significant association between ATH status and CIMT, CAC or brachial artery FMD was found after adjustment for the use of alcohol, dairy products and all other major risk factors of coronary artery disease. In otherwise similar statistical analysis, the results remained non-significant when females and males were analysed in their own groups. In conclusion, the finding does not support the involvement of ATH in the pathogenesis of early atherosclerosis.

Can primary hypolactasia manifest itself after the age of 20 years? A two-decade follow-up study

OBJECTIVE

The age at manifestation of primary hypolactasia varies between ethnic groups. Many people report experiencing the first symptoms of lactose intolerance at adult age. The purpose of this study was to investigate whether primary hypolactasia can appear after the age of 20 among the Finnish population and to investigate the outcome of different diagnostic methods of lactose maldigestion.

MATERIAL AND METHODS

Lactose digestion status was assessed by the lactose tolerance test with ethanol (LTTE) in 42 subjects (38-71 years) who reported having gastrointestinal symptoms after the ingestion of 20 g or less of lactose and who were diagnosed as lactose digesters in earlier studies. Thirteen of the study subjects underwent upper gastrointestinal endoscopy, and 35 gave a blood sample for DNA analysis.

RESULTS

Only one of the 42 subjects studied had the genotype C/C(-13910) indicating hypolactasia. Lactase activity was higher in those with the genotype T/T (69.2 U/g protein) than in those with the heterozygous genotype C/T (36.3 U/g protein) (p=0.017).

CONCLUSIONS

Although primary hypolactasia normally appears before the age of 20 years, the decline in lactase activity may on rare occasions continue after that age. Genotyping of the C/T(-13910) variant was found to be a reliable diagnostic approach in defining the lactase persistence/non-persistence status of the study subjects.

Decline of lactase activity and c/t-13910 variant in Sardinian childhood

OBJECTIVES

Our study aims to determine the age of onset of adult-type hypolactasia in Sardinians, and to establish the age at which genotyping of the C/T-13910 variant can be used reliably in the diagnosis of lactose malabsorption.

PATIENTS AND METHODS

A lactose breath hydrogen test was given to 383 randomly selected patients, from 3 to 19 years old.

RESULTS

The C/C-13910 genotype was found in 90% of patients; the frequency of the positive lactose breath hydrogen test increased with age and reached a prevalence of 85% at 9 years.

CONCLUSIONS

In Sardinians, adult-type hypolactasia becomes phenotypically evident in all individuals older than 9 years, suggesting that this should be considered the minimum age at which the genetic test for lactase nonpersistence should be applied.

Evolution of Infant and Young Child Feeding: Implications for Contemporary Public Health

Evolutionary anthropological and ethnographic studies are used to develop a general conceptual framework for understanding prehistoric, historic, and contemporary variation in human lactation and complementary feeding patterns. Comparison of similarities and differences in human and nonhuman primate lactation biology suggests humans have evolved an unusually flexible strategy for feeding young. Several lines of indirect evidence are consistent with a hypothesis that complementary feeding evolved as a facultative strategy that provided a unique adaptation for resolving tradeoffs between maternal costs of lactation and risk of poor infant outcomes. This evolved flexibility may have been adaptive in the environments in which humans evolved, but it creates potential for mismatch between optimal and actual feeding practices in many contemporary populations.

The effects of adult-type hypolactasia on body height growth and dietary calcium intake from childhood into young adulthood: a 21-year follow-up study--the Cardiovascular Risk in Young Finns Study

OBJECTIVE

The effect of adult-type hypolactasia, caused by the lactase-phlorizin hydrolase C/C-13910 genotype, on growth is unknown. We studied whether this polymorphism was associated with body height growth, the use of milk products, or dietary calcium intake.

METHODS

A prospective cohort study was performed among 3596 randomly selected Finnish children and adolescents (3-18 years of age) in 1980, with reexamination in 1983, 1986, and 2001 (after a 21-year follow-up period). Lactase-phlorizin hydrolase C/T-13910 polymorphism was determined for 2265 participants in 2002. Nutrient intakes were measured for 1137, 858, and 1031 subjects in 1980, 1986, and 2001, respectively.

RESULTS

The lactase-phlorizin hydrolase C/T-13910 polymorphism was not related to mean height growth speed for either boys or girls or to final mean body height in adulthood. The consumption of milk products, protein, and calcium was lowest for female subjects with the lactase-phlorizin hydrolase C/C-13910 genotype over the study years, but there were no genotype-related differences in the intake of vitamin D. For boys, significant differences were found in the consumption of milk products but not in the mean dietary intake of calcium, protein, or vitamin D.

CONCLUSIONS

The lactase-phlorizin hydrolase C/C-13910 genotype was not associated with mean growth speed or final mean body height for either boys or girls. However, it contributed significantly to milk product consumption and dietary calcium intake from childhood into young adulthood.

Identification of a variant associated with adult-type hypolactasia

Adult-type hypolactasia, also known as lactase non-persistence (lactose intolerance), is a common autosomal recessive condition resulting from the physiological decline in activity of the lactase-phlorizin hydrolase (LPH) in intestinal cells after weaning. LPH hydrolyzes lactose into glucose and galactose. Sequence analyses of the coding and promoter regions of LCT, the gene encoding LPH, has revealed no DNA variations correlating with lactase non-persistence. An associated haplotype spanning LCT, as well as a distinct difference in the transcript levels of 'non-persistence' and 'persistence' alleles in heterozygotes, suggest that a cis-acting element contributes to the lactase non-persistence phenotype. Using linkage disequilibrium (LD) and haplotype analysis of nine extended Finnish families, we restricted the locus to a 47-kb interval on 2q21. Sequence analysis of the complete region and subsequent association analyses revealed that a DNA variant, C/T-13910, roughly 14 kb upstream from the LCT locus, completely associates with biochemically verified lactase non-persistence in Finnish families and a sample set of 236 individuals from four different populations. A second variant, G/A-22018, 8 kb telomeric to C/T-13910, is also associated with the trait in 229 of 236 cases. Prevalence of the C/T-13910 variant in 1,047 DNA samples is consistent with the reported prevalence of adult-type hypolactasia in four different populations. That the variant (C/T-13910) occurs in distantly related populations indicates that it is very old.

Ineffectiveness of breath methane excretion as a diagnostic test for lactose malabsorption

BACKGROUND

In clinical and field conditions, breath gas analysis has been widely used in evaluating carbohydrate digestion. A field study was performed to determine the prevalence of lactose malabsorption in Myanmar children and to evaluate the possibility of using breath methane excretion to indicate lactose malabsorption in a field situation.

METHODS

The study population consisted of 118 children aged 1 to 12 years. A hydrogen breath test after a lactose meal (2 g/kg, maximum 50 g) was used as a standard test.

RESULTS

Lactose malabsorption was detected in 16.7% of children aged 1 to 2.9 years, with the prevalence increasing with age from 40.5% of those aged 3 to 5.9 years to 88.5% of those aged 6 to 8.9 years and reaching 91.7% in those aged 9 to 11.9 years. Lactose malabsorption was more prevalent when children were weaned before 4 months of age (87.2 vs. 41.1%; p < 0.01). Compared with lactose-tolerant children, those with lactose malabsorption had significantly higher concentrations of breath hydrogen excretion 60 minutes after the lactose test meal. Breath methane excretion was also significantly higher in samples at 120 minutes in children with lactose malabsorption. Breath methane excretion of greater than or equal to 2 parts per million at 180 minutes as a diagnostic test for lactose malabsorption had a sensitivity of 61.5% and a specificity of 84.6%.

CONCLUSION

The breath methane test for lactose malabsorption has a lower sensitivity and specificity than the breath hydrogen test and therefore does not replace the lactose breath hydrogen test.

Assignment of the locus for congenital lactase deficiency to 2q21, in the vicinity of but separate from the lactase-phlorizin hydrolase gene

Congenital lactase deficiency (CLD) is an autosomal recessive, gastrointestinal disorder characterized by watery diarrhea starting during the first 1-10 d of life, in infants fed lactose-containing milks. Since 1966, 42 patients have been diagnosed in Finland. CLD is the most severe form of lactase deficiency, with an almost total lack of lactase-phlorizin hydrolase (LPH) activity on jejunal biopsy. In adult-type hypolactasia, the most common genetic enzyme deficiency in humans, this enzyme activity is reduced to 5%-10%. Although the activity of intestinal LPH has been found to be greatly reduced in both forms, the molecular pathogenesis of lactase deficiencies is unknown. On the basis of the initial candidate-gene approach, we assigned the CLD locus to an 8-cM interval on chromosome 2q21 in 19 Finnish families. At the closest marker locus, a specific allele 2 was present in 92% of disease alleles. On the basis of a genealogical study, the CLD mutation was found to be enriched in sparsely populated eastern and northern Finland, because of a founder effect. The results of both the genealogical study and the haplotype analysis indicate that one major mutation in a novel gene causes CLD in the Finnish population. Consequently, the critical region could be restricted further, to an approximately 350-kb interval, by ancient-haplotype and linkage-disequilibrium analyses. Surprisingly, the LPH gene was shown to lie outside the critical CLD region, excluding it as a causative gene for CLD. The LPH locus was found to reside >2 Mb from the critical CLD region.

Comparison of a portable breath hydrogen analyser (Micro H2) with a Quintron MicroLyzer in measuring lactose maldigestion, and the evaluation of a Micro H2 for diagnosing hypolactasia

The measurement of hydrogen in exhaled air and changes in the concentration of blood glucose and urine galactose excretion are indirect methods of diagnosing hypolactasia. The aim of this study was to compare a portable breath hydrogen analyser (Micro H2) with a widely used model (Quintron MicroLyzer) and to compare them with the blood glucose, urine galactose, and gastrointestinal symptoms in the lactose tolerance test. After an overnight fast, 44 volunteers (18-66 y) ingested 50 g lactose in a single oral dose. Changes in exhaled breath hydrogen concentrations were measured with the two analysers, and changes in blood glucose and urinary galactose were assayed for 4 h and used as a reference. Eighteen subjects were diagnosed as maldigesters according to our gold standard of at least two positive tests out of the three: breath hydrogen by Quintron, blood glucose concentration, and urine galactose excretion. The highest increase in the breath hydrogen concentration over the baseline was highly variable: 44-366 ppm (Micro H2) or 27-187 ppm (Quintron MicroLyzer). The sensitivity, specificity, and positive and negative predictive values of the Micro H2 compared to the gold standard were 83%, 96%, 94% and 89%, respectively. Overall agreement was 91% (95% CI 78-97%). Compared to the Quintron, the diagnoses were identical in 100% of the cases (92-100%). Thus, for diagnosing hypolactasia, the Micro H2 appeared as reliable for measuring breath hydrogen concentrations as Quintron MicroLyzer commonly used in oral lactose tolerance tests.

Human adult-onset lactase decline: an update

Human adult-onset lactase decline is a biologic feature characteristic of the maturing intestine in the majority of the world's population. The digestion and absorption of lactose, the major carbohydrate in milk and also the main substrate for lactase, is often variable, a consequence of lactase levels, gastric emptying rate, and colonic salvage. Although commercially available "lactase" products alleviate symptoms in many lactose-intolerant people, a greater understanding of this variability in lactose tolerance could lead to interventions that reduce the rate of gastric emptying and/or increase the proliferation of lactose-metabolizing bacteria in the colon, leading to more efficient lactose utilization. Adult-onset lactase decline appears to be a risk factor for developing osteoporosis, owing to avoidance of dairy products or interference of undigested lactose with calcium absorption. Elderly with both adult-onset lactase decline and atrophic gastritis or those undergoing anti-ulcer treatment may have an increased risk of low calcium absorption owing to the lack of gastric acid that facilitates calcium uptake. Thus, lactose-intolerant elders should monitor their calcium nutrition status carefully.

Lactose digestion capacity and perceived symptomatic response after dairy product consumption in Tokelau Island migrants

When lactose-malabsorbing individuals use dairy products decreased lactase activity and the subsequent reduction in hydrolysis of ingested lactose can result in gastrointestinal and gaseous symptoms (lactose intolerance). This article examines lactose malabsorption, perceived gastrointestinal symptoms, and dairy product consumption in a Tokelau Island migrant population in New Zealand. Questionnaire data were collected and lactose digestion capacity was determined for 58 individuals 15-71 years of age. Additional questionnaire data were collected for 137 Tokelau migrants, 18-50 years of age. Breath hydrogen analysis indicated that 63.8% (CI = 51.4-76.2%) of Tokelau migrants were lactose malabsorbers, while 22.4% (11.7-33.1%) can absorb lactose [results are inconclusive for 13.8% (4.9-22.7%) of the population]. This was consistent with results reported for other Polynesian populations. Tokelau Island migrants reported relatively low levels of gastrointestinal distress after the consumption of daily products. Less than 50% of those with lactose malabsorption perceived gastrointestinal symptoms after a 50 g of lactose in 300 ml of water, while one third of this group reported symptoms after approximately 240 ml (one glass) or less of milk. However, without confirmation by double-blind studies, it is difficult to state the extent to which symptoms are actually due to lactose. Neither the ability to absorb lactose nor perceived gastrointestinal symptoms are associated with the frequency or quantity of dairy product consumption (P > 0.05). Patterns of dairy product consumption are just as likely due to other physiological, psychological, cultural, and social factors. Am. J. Hum. Biol. 9:233-246, 1997. © 1997 Wiley-Liss, Inc.

Lactose malabsorption in Khants in western Siberia

BACKGROUND

We wanted to estimate the prevalence of selective lactose malabsorption (SLM) in Khants, a small Finno-Ugric population living in Western Siberia who have traditionally consumed no milk in adulthood.

METHODS

A total of 80 Khants, aged 8-57 years and living on the middle reaches of the River Ob, were studied. The diagnosis was based on a lactose tolerance test; general malabsorption was excluded by a glucose-galactose tolerance test whenever possible. In six subjects electronmicroscopic examination of the duodenal mucosa was performed.

RESULTS

The prevalence of SLM in the Khants was 94%.

CONCLUSION

This is the highest prevalence found in the previous Soviet Union.

Hypolactasia and lactase persistence. Historical review and the terminology

Lactase (more precisely lactase-phlorizin hydrolase) is located in the brush border of the small intestinal enterocytes and is responsible for the hydrolysis of dietary lactose. The earliest studies on lactase activity in mammals were published around the turn of the century. In 1903, it was found that the dog had a very low lactase activity and therefore lactose remained unhydrolysed, causing diarrhoea. Human hypolactasia was demonstrated in 1963, and it was soon found that it is very common, commoner than lactase persistence in most parts of the world. In 1973, adult-type hypolactasia was shown to be inherited by an autosomal recessive single gene. This article reviews the early expansion of the knowledge on lactase and hypolactasia as well as the correct terminology.

Diagnosis of hypolactasia and lactose malabsorption

The article briefly describes the various methods that are available for diagnosing hypolactasia. Special attention is drawn to the fact that different methods are useful at different levels of the health care organization. When the test result indicates lactose malabsorption, general malabsorption should be excluded by a glucose-galactose tolerance test, for example. If the glucose-galactose tolerance test produces a normal result, it can be assumed that the patient has primary adult-type selective lactose malabsorption. The possibility of secondary lactose malabsorption must be excluded according to the principles described by Villako & Maaroos (104).

Genetics and epidemiology of adult-type hypolactasia

The prevalence of adult-type hypolactasia varies from less than 5% to almost 100% between different populations of the world. The lowest prevalence has been found in northwestern Europe, around the North Sea, and the highest prevalence in the Far East. The reason for the variation is that selective (primary) hypolactasia is genetically determined by an autosomal recessive single gene. It is assumed that thousands of years ago all people had hypolactasia in the same way as most mammals do today. At that time in cultures where milk consumption was started after childhood, lactase persistence had a selective advantage. Those people with lactase persistence were healthier and had more children than people with hypolactasia, and the frequency of the lactase persistence gene started to increase. The present prevalence of hypolactasia can be explained fairly well by this culture historical hypothesis. This article reviews the evidence for the inheritance of adult-type hypolactasia and the occurrence of hypolactasia in different countries and populations of the world.

Metabolism of lactose in the human body

The article describes the metabolism of lactose in both normo- and hypolactasia in the human body. Attention is drawn to the differences in lactose tolerance among lactose malabsorbers.

Clinical picture of hypolactasia and lactose intolerance

Selective adult-type hypolactasia, the main cause of primary malabsorption of lactose, shows considerable variation in terms of its symptoms, which mainly depend on the amount of milk consumption. The article discusses congenital lactase deficiency and familial lactose intolerance. Links between hypolactasia and non-specific abdominal complaints, coronary heart disease and cataract are presented. The decrease in lactase activity in the brush border of jejunal mucosa, associated with diseases of the mucosa or any other condition which damages the enterocytes, is discussed as a cause of secondary hypolactasia. It is shown that adult-type primary hypolactasia and selective lactose malabsorption represent a major problem in the everyday work of general practitioners, particularly in populations where hypolactasia is common. Therefore, the examination and treatment of non-selected patients with vague abdominal complaints is important in primary health care. As the need for calcium in humans is largely met by the intake of milk, the consumption of milk has to be in amounts that are tolerable for the individual.

Time required for gene frequency change in a deterministic model of gene-culture coevolution, with special reference to the lactose absorption problem

The time required for gene frequency change under natural selection in a deterministic model of gene-culture coevolution is investigated. A discrete generations model is formulated, and its continuous time approximation is derived. In passing to the continuous time limit, it is assumed that the frequency of the culturally transmitted trait does not change under oblique (between generations) transmission. The system of ordinary differential equations thus obtained are solved, and the dependence on the parameters of horizontal (within generations) transmission and natural selection is examined. The time required is found to be substantially longer when the determination of a phenotypic difference subject to natural selection is partly cultural rather than completely genetic. The predictions are relevant to the possibility of the coevolution of lactose absorbers and milk drinkers in some human populations. Alternative hypotheses are briefly discussed in the light of the theoretical results.

Lactose malabsorption in Australian Aboriginal children

The purpose of this study was to determine the prevalence of lactose malabsorption in healthy full-blood Australian Aboriginal children. Sixty-three Aboriginal subjects and forty-six non-Aboriginal controls ranging in age from six to 14 years were tested using the breath hydrogen method. Seventy percent of the Aboriginal subjects were found to be lactose malabsorbers and 9% of the controls. The results provide strong evidence that the majority of full-blood Aboriginal children are lactose malabsorbers and that the characteristic is well-established by 6-7 years of age, in common with most other non-Western populations.

Hypolactasia in a fixed cohort of young Finnish adults. A follow-up study

Selective late-onset hypolactasia (lactose malabsorption) was examined in a fixed cohort of Finnish adolescents, now aged 17 to 25 years. This was the third examination of the same subjects. In the first examination 10 years ago the prevalence of hypolactasia was 6.2%. In the second examination 5 years ago three more cases of hypolactasia were diagnosed, and the prevalence was 9.3%. In this examination the prevalence was 10.3% (10/97); 2 newly manifested hypolactasia cases were diagnosed. If those subjects were included who were not examined this time but whose hypolactasia was diagnosed previously or who were at least 20 years old at the second examination, the prevalence of hypolactasia was 12.7% (13/102). In the 17- to 20-year-olds the prevalence was 15.4%, and in the 21- to 25-year-olds it was 11.1%. The results were in agreement with our previous conclusions that hypolactasia manifests itself in the Finnish population mostly between 10 and 20 years of age and that the prevalence in adults is 17%. Eight of the 13 subjects with hypolactasia had weekly abdominal symptoms; all except one of them had symptoms after the lactose tolerance test. Nine subjects had realized milk intolerance; six of them had symptoms from one glass of milk or less. Symptoms varied considerably from person to person, the commonest symptom being meteorism. The reason was probably the variation in the remaining small-intestinal lactase activity and in the functional stability of the colon.

Clinical findings and intestinal immunoglobulins in children with partial IgA deficiency

We studied the intestinal morphology, and the jejunal and rectal immunoglobulins of 16 children with partial IgA deficiency, defined as serum IgA concentration more than two standard deviations below the mean for age, but higher than the lower limit of sensitivity of single radial immunodiffusion (0.02 g/l). Five of the patients had been treated with phenytoin, 2 had juvenile rheumatoid arthritis, 2 had ulcerative colitis and 5 had recurrent upper respiratory tract infections. The jejunal morphology was normal in every case. In 6 cases normalization of serum IgA occurred during the follow-up, while in one patient with ulcerative colitis the concentration fell below 0.02 g/l. In patients with recurrent infections, there was a decreased frequency of infections when the level of serum igA increased. In 4 patients, IgM-containing cells prodominated in both the jejunal and rectal mucosa, and IgM was increased in the intestinal juice. In 6 patients a significant increase in IgM-containing cells or a decrease in IgA-containing cells or both were seen in either the rectal or jejunal mucosa. There was no correlation between the number of IgA-containing cells in the intestinal mucosa and the serum level of IgA.

The geographic hypothesis and lactose malabsorption. A weighing of the evidence

Reviewed in this article is evidence bearing on the geographic hypothesis advanced eight years ago to explain the striking ethnic or racial differences in prevalence of primary adult lactose malabsorption that are found around the world. Most evidence is found to support the hypothesis and the likelihood that some human groups came to have low prevalences of such lactose malabsorption because of selective pressures over a long historical period that favored the adult lactose absorber under particular ecological conditions.

Manifestation and occurrence of selective adult-type lactose malabsorption in Finnish teenagers. A follow-up study

In 1969--1970, a simple random sample of 129 Finnish school-aged children was examined to study selective adult-type lactose malabsorption (SLM) in this age category. SLM was found in 8 children. All subjects were reexamined 5 years later. SLM was reconfirmed in these 8 persons and found in 3 additional subjects who had normal lactose absorption in the first examination. The prevalence of SLM was 9.3%, being 8.5% in the age category 12--15 years and 9.9% in that 16--20 years. Low rise of blood glucose in the lactose tolerance test of the first examination, very low milk consumption, milk intolerance, and history of gastrointestinal symptoms were found to be of low predictive value as indicators of SLM. It was also concluded that information about dietetic sources of lactose is important to persons with SLM, but categorical exclusion of lactose from the diet is not necessary, at least in the Finnish population.

Diagnostic value of disaccharide tolerance tests in children

Diagnostic value of disaccharide tolerance tests in children. Acta Paediatr Scand, 64:693, 1975.--The diagnostic value of oral lactose and sucrose tolerance tests was investigated in 61 children. A total of 105 oral disaccharide tests were carried out. When the rise in blood sugar was low, the same disaccharide was, as a control measure, instilled directly into the small intestine through a tube. This was carried out in 40 cases. In 21 patients the rise in blood sugar following the two forms of administration was correlated with the disaccharidase activity in a peroral small-intestine biopsy. The incidence of false-positive oral lactose tests was between 23 and 30%, that of false-positive oral sucrose tests between 24 and 33%. A border value of 20 mg per 100 ml in the rise of blood glucose within the first hour following a direct intra-intestinal administration affords a very satisfactory distinction between patients with and without disaccharide malabsorption. Blood glucose determinations exceeding one hour were found to be without diagnostic value.