Congruency of Genetic Predisposition to Lactase Persistence and Lactose Breath Test

The physiological decline of lactase production in adulthood, in some individuals, is responsible for the so-called “Lactose Intolerance.” This clinical syndrome presents with gastrointestinal and non-gastrointestinal symptoms following the consumption of dairy containing food. Lactose intolerance can be evaluated by means of the Lactose Breath Test (phenotype) and/or genetic evaluation of lactase-gene polymorphism (genotype). A comparison of the two tests was carried out in a large number of symptomatic adult subjects, which are selected and not representative of the general population. Congruency was as high as 88.6%. Among lactase non-persistent (genotype C/C), 14 subjects showed a negative Lactose Breath Test (LBT), possibly due to young age. Among lactase-persistent (genotype C/T), four subjects showed a positive LBT, which helps to diagnose secondary lactose intolerance. Symptoms, both gastrointestinal and extra-gastrointestinal, were reported by 90% of patients during the breath test. Clinical use of both tests in the same patients could be taken into consideration as a sharp diagnostic tool. We suggest considering the use of the genetic test after LBT administration, when secondary hypolactasia is suspected, for completion of diagnostic procedures.

Assessment of Lactose-Free Diet on the Phalangeal Bone Mineral Status in Italian Adolescents Affected by Adult-Type Hypolactasia

Adult-type hypolactasia (ATH) is a clinical syndrome of primary lactase deficiency. A lactose-free diet is advisable to avoid the symptoms linked to the condition, but this potentially creates problems for optimal bone mineralization due to reduced calcium intake. To evaluate the effect of the lactose-free diet on the bone mineral status (BMS), we compared the phalangeal BMS of adolescents with ATH to that of peers on a normal diet. Also, we analyzed the correlations between BMS and dietary behavior, physical exercise, and calcium and vitamin D intake. A total of 102 cases and 102 healthy controls filled out a diet record and underwent phalangeal Quantitative Ultrasound (QUS). No difference in BMS was observed. The time spent on lactose-free diet (4.8 ± 3.1 years) was inversely correlated to the BMS. More than 98% of cases consumed lactose-free milk, but calcium and vitamin D intake were significantly lower. Calcium intake was correlated to physical exercise but not to BMS. Our results suggest that a lactose-free diet does not affect the phalangeal BMS of adolescents with primary lactase deficiency when their diet includes lactose-free cow’s milk. However, there is still a significantly lower calcium intake than in the population reference. The inverse correlation observed between the BMS and the time spent on a lactose-free diet suggests that a long-term follow-up is advisable.

Study on influence of age, gender and genetic variants on lactose intolerance and its impact on milk intake in adult Asian Indians

BACKGROUND

Lactase non-persistence (LNP) has been associated with the CC genotype of -13910C > T and GG genotype of -22018G > A polymorphisms present upstream of the lactase gene. Lactose intolerance (LI) is caused when gastrointestinal symptoms develop in individuals with low lactase activity.

OBJECTIVE

To analyse association of LNP genotype and LI symptoms with milk intake and determine whether factors such as age, gender and genotype affect LI status.

SUBJECTS AND METHODS

Genetic analysis and lactose tolerance test (LTT) were performed on 205 healthy Indian adults. The pattern of milk consumption was recorded using a dietary questionnaire.

RESULTS

LI was strongly associated with -13910CC genotype (OR = 10.28, 95% CI = 2.32-45.55, p = 0.002). Females were found to be at a higher risk of developing LI (OR = 2.47, 95% CI = 1.33-4.59, p = 0.004). The association of the ≥50 years age group with LI was marginally significant (OR = 1.86, 95% CI = 0.995-3.47, p = 0.05). Frequency and quantity of milk intake were lower in subjects belonging to the LNP genotype and LI groups (p < 0.05).

CONCLUSIONS

Subject study suggests that gender and genotype may be associated with development of LI. Association of age with LI was marginal. The data also indicate that LNP genotype and LI may play a role in influencing milk intake in individuals.

Protein-losing enteropathy following the Fontan procedure in a child with intestinal lactase deficiency treated with lactose-free diet

A 12-year-old girl presented with a protein-losing enteropathy. Symptoms started 4 weeks after undergoing the Fontan procedure at the age of 1.5 years for mitral atresia, ventricular septal defect, and double-outlet right ventricle. Upon referral for 3 weeks of rehabilitation after multiple interventional measures and drug treatments, she appeared in a dystrophic state, with decreased plasma protein and electrolyte levels along with occasional tetanic convulsions. Blood glucose levels after a lactose tolerance test were markedly reduced. The introduction of a lactose-free diet was quickly effective, with plasma protein and electrolyte levels raised to normal levels, and the girl's body weight increased without ascites or oedema. Molecular genetic examination revealed a homozygous C/C13910 polymorphism in the LCT gene.

CONCLUSION

Protein-losing enteropathy in the Fontan circulation may be provoked by lactase deficiency and should therefore be ruled out to exclude this rather common condition.

Association between celiac disease and primary lactase deficiency

Primary lactase deficiency (PLD) is a common inherited condition caused by a reduced activity of lactase. Two single-nucleotide polymorphisms C/T(-13910) and G/A(-22018) upstream of the lactase gene are associated with lactase nonpersistence. In celiac disease (CD) patients, lactose intolerance could be due to secondary lactase deficiency and to PLD. The aim of this study were to evaluate the association of PLD and CD using genetic test, and to define the prevalence of PLD in celiac subjects compared with a control population. A total of 188 controls and 92 biopsy-proven CD patients were included in the study. More than 70% of all subjects were found homozygous for the polymorphisms. Differences in the prevalence of PLD were not found between CD patients and controls.In conclusions, the hereditary lactase deficiency is frequent in Italian CD children as in control population.

Meta-analysis: the diagnostic accuracy of lactose breath hydrogen or lactose tolerance tests for predicting the North European lactase polymorphism C/T-13910

BACKGROUND

  The diagnostic accuracy of two indirect tests of lactose digestion, lactose breath hydrogen and lactose tolerance tests, have not been systematically reviewed for comparison with available publications on genotype.

AIM

  To perform a meta-analysis of available studies that compares the north-European genetic polymorphism C/T-13910 with the lactose breath hydrogen and the lactose tolerance tests, to determine their ability to predict geno/phenotype relationships. We examine the effects of lactose loading dose, inclusion of children and latitudes of study centre on comparative outcome.

METHODS

  An electronic database of the literature as well as individual references in articles were searched with the theme of genetics of lactase and comparisons with breath or lactose tolerance tests were carried out. Random effect and fixed effect models were used for breath and lactose tolerance tests respectively, to report summary accuracy measures with 95% confidence intervals (CI).

RESULTS

  The search revealed 19 studies: 17 evaluated breath hydrogen, five lactose tolerance test (3/17 overlapped). Overall sensitivity was 0.88 (CI, 0.85-0.90), specificity was 0.85 (CI, 0.82-0.87) for breath test. Heterogeneity was explored by adjusting for studies including children, high or low dose lactose and to some extent by site of study. The lactose tolerance test showed sensitivity of 0.94 (0.9-0.97) and specificity of 0.90 (0.84-0.95) with a nonsignificant heterogeneity.

CONCLUSION

  The diagnostic accuracy of both tests individually reflects expected geno/phenotypes when the populations are well defined.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Analysis of three functional polymorphisms in relation to osteoporosis phenotypes: replication in a Spanish cohort

Osteoporosis is a complex disease involving many putative genetic factors. Association analysis of functional SNPs in candidate genes is an important tool for their identification. However, this approach is affected by limited power, population stratification, and other drawbacks that lead to discordant results. Replication in independent cohorts is essential. We performed association analyses of three functional polymorphisms previously associated with bone phenotypes--namely, Ala222Val in MTHFR, Ile1062Val in LRP6, and -13910C>T in LCT--in a cohort of 944 postmenopausal Spanish women, all of them with lumbar spine (LS) bone mineral density (BMD) data and most with femoral neck (FN) BMD and fracture data. We found significant differences between genotypes only for the MTHFR polymorphism and vertebral factures, with an OR of 2.27 (95% CI 1.17-4.38) for the TT vs. CC/CT genotypes, P = 0.018. We present genotype and allele frequency data for LCT -13910C>T for a Spanish population, where the T allele (conferring lactase persistence) has a frequency of 38.6%. Genotype frequencies were consistent with observed clines in Europe and with the prevalence of lactase nonpersistence. The LCT -13910C>T polymorphism was significantly associated with height and weight, such that T allele carriers were 0.88 cm taller (95% CI 0.08-1.59 cm, P = 0.032, adjusted by age) than CC individuals and TT homozygotes were 1.91 kg heavier than CC/CT individuals (95% CI 0.11-3.71 kg, P = 0.038, adjusted by age). In conclusion, no significant association was observed between the studied polymorphisms and LS BMD or FN BMD in postmenopausal Spanish women, and only MTHFR Ala222Val was associated with vertebral fractures.

The -22018A allele matches the lactase persistence phenotype in northern Chinese populations

OBJECTIVE

It has been reported that some single-nucleotide polymorphisms (-13910C/T, -22018G/A, -13907C/G, -13915T/G, and -14010G/C) within the lactase gene are associated with lactase persistence. In our previous study, we found that -13910C/T is not a good predictor of lactase persistence in Chinese populations. To obtain a better understanding of the mechanism of lactase persistence, we examined the frequencies in Northern China of the four other alleles that are associated with lactase persistence.

MATERIAL AND METHODS

We evaluated the allele frequencies of -22018G/A, -13907C/G, -13915T/G, and -14010G/C in six northern Chinese populations (Manchu, Mongol, Hezhen, Oroqen, Kazak, and northern Han) using the methods of polymerase chain reaction-restriction fragment length polymorphism and resequencing.

RESULTS

By genotyping 1092 chromosomes, we found that the frequency of the -22018A allele was highest in the Kazak population and extremely low in the northern Han population. Although there are little available data about the frequency of lactase persistence in northern Chinese populations, we compared the allele frequencies with the phenotype frequencies that have been published previously. We found that the frequency of the -22018A allele was basically consistent with the reported frequencies of lactase persistence in Northern China. With respect to the -13907C/G, -13915T/G, and -14010G/C polymorphisms, we found no individuals with the derived allele.

CONCLUSIONS

The frequency of the -22018A allele differed significantly among the six populations and the frequency reflected the frequency of lactase persistence. Taking into consideration the results of previous studies, we believe that the origins of lactase persistence-associated alleles are different in different pastoral populations.

A worldwide correlation of lactase persistence phenotype and genotypes

BACKGROUND

The ability of adult humans to digest the milk sugar lactose - lactase persistence - is a dominant Mendelian trait that has been a subject of extensive genetic, medical and evolutionary research. Lactase persistence is common in people of European ancestry as well as some African, Middle Eastern and Southern Asian groups, but is rare or absent elsewhere in the world. The recent identification of independent nucleotide changes that are strongly associated with lactase persistence in different populations worldwide has led to the possibility of genetic tests for the trait. However, it is highly unlikely that all lactase persistence-associated variants are known. Using an extensive database of lactase persistence phenotype frequencies, together with information on how those data were collected and data on the frequencies of lactase persistence variants, we present a global summary of the extent to which current genetic knowledge can explain lactase persistence phenotype frequency.

RESULTS

We used surface interpolation of Old World lactase persistence genotype and phenotype frequency estimates obtained from all available literature and perform a comparison between predicted and observed trait frequencies in continuous space. By accommodating additional data on sample numbers and known false negative and false positive rates for the various lactase persistence phenotype tests (blood glucose and breath hydrogen), we also apply a Monte Carlo method to estimate the probability that known lactase persistence-associated allele frequencies can explain observed trait frequencies in different regions.

CONCLUSION

Lactase persistence genotype data is currently insufficient to explain lactase persistence phenotype frequency in much of western and southern Africa, southeastern Europe, the Middle East and parts of central and southern Asia. We suggest that further studies of genetic variation in these regions should reveal additional nucleotide variants that are associated with lactase persistence.