Maternal inheritance of a promoter variant in the imprinted PHLDA2 gene significantly increases birth weight.

Birth weight is an important indicator of both perinatal and adult health, but little is known about the genetic factors contributing to its variability. Intrauterine growth restriction is a leading cause of perinatal morbidity and mortality and is also associated with adult disease. A significant correlation has been reported between lower birth weight and increased expression of the maternal PHLDA2 allele in term placenta (the normal imprinting pattern was maintained). However, a mechanism that explains the transcriptional regulation of PHLDA2 on in utero growth has yet to be described. In this study, we sequenced the PHLDA2 promoter region in 263 fetal DNA samples to identify polymorphic variants. We used a luciferase reporter assay to identify in the PHLDA2 promoter a 15 bp repeat sequence (RS1) variant that significantly reduces PHLDA2-promoter efficiency. RS1 genotyping was then performed in three independent white European normal birth cohorts. Meta-analysis of all three (total n = 9,433) showed that maternal inheritance of RS1 resulted in a significant 93 g increase in birth weight (p = 0.01; 95% confidence interval [CI] = 22-163). Moreover, when the mother was homozygous for RS1, the influence on birth weight was 155 g (p = 0.04; 95% CI = 9-300), which is a similar magnitude to the reduction in birth weight caused by maternal smoking.

Change in paternal grandmothers' early food supply influenced cardiovascular mortality of the female grandchildren.

BACKGROUND: This study investigated whether large fluctuations in food availability during grandparents' early development influenced grandchildren's cardiovascular mortality. We reported earlier that changes in availability of food - from good to poor or from poor to good - during intrauterine development was followed by a double risk of sudden death as an adult, and that mortality rate can be associated with ancestors' childhood availability of food. We have now studied transgenerational responses (TGR) to sharp differences of harvest between two consecutive years' for ancestors of 317 people in Överkalix, Sweden. RESULTS: The confidence intervals were very wide but we found a striking TGR. There was no response in cardiovascular mortality in the grandchild from sharp changes of early exposure, experienced by three of the four grandparents (maternal grandparents and paternal grandfathers). If, however, the paternal grandmother up to puberty lived through a sharp change in food supply from one year to next, her sons' daughters had an excess risk for cardiovascular mortality (HR 2.69, 95% confidence interval 1.05-6.92). Selection or learning and imitation are unlikely explanations. X-linked epigenetic inheritance via spermatozoa seemed to be plausible, with the transmission, limited to being through the father, possibly explained by the sex differences in meiosis. CONCLUSION: The shock of change in food availability seems to give specific transgenerational responses.

Paternal grandmother's smoking in pregnancy is associated with extreme aversion to bitter taste in their grandchildren.

Although there are many examples in the experimental literature of an environmental exposure in one generation impacting the phenotypes of subsequent generations, there are few studies that can assess whether such associations occur in humans. The Avon Longitudinal Study of Parents and Children (ALSPAC) has, however, been able to determine whether there are associations between grandparental exposures and their grandchildren's development. Several of our studies, including sensitivity to loud noise, have shown associations between a grandmother smoking in pregnancy and the phenotype of the grandchild. These results were mostly specific to the sex of the grandchild and to whether the prenatal (i.e. during pregnancy) smoking occurred in the maternal or paternal grandmother. Here, we have used ancestral data on prenatal smoking among the grandmothers of the ALSPAC index children to examine possible effects on the grandchild's ability to detect the bitter taste of PROP (6 n-propylthiouracil), distinguishing between the 10% deemed 'extreme tasters', and the rest of the population (total N = 4656 children). We showed that grandchildren whose paternal (but not maternal) grandmothers had smoked in pregnancy were more likely than those of non-smoking grandmothers to be extreme tasters [odds ratio (OR) 1.28; 95% confidence interval (CI) 1.03, 1.59] and that this was more likely in granddaughters (OR 1.42; 95% CI 1.03, 1.95) than grandsons (OR 1.18; 95% CI 0.88, 1.60). This pattern of association between paternal foetal exposure and the granddaughter's development has been found with several other outcomes, suggesting that investigations should be undertaken to investigate possible mechanisms.

Unexpected Associations between the Number of FRAXE Repeats in Boys and Evidence of Diabetes in Their Mothers and Maternal Grandmothers.

The FRAXE section of the FMR2 gene, located on the X chromosome, contains varying numbers of trinucleotide repeats; boys with over 200 repeats tend to have mild cognitive impairments, though this is rare. Little is known, however, concerning the phenotypes of individuals with smaller numbers of repeats. Here we answer the research question as to whether the health of ancestors of boys from whom the relevant X chromosome was inherited differed in any way according to the number of FRAXE repeats. Numbers of FRAXE repeats in 5057 boys from the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed. The distribution was bimodal, with the second smaller distribution starting at 22 repeats. We tested whether possession of 22+ repeats was associated with differences in the health of mothers (who share the X chromosome) and maternal grandmothers (half of whom share it). Female ancestors of boys with >21 repeats compared with <22 showed that maternal grandmothers (MGM) and mothers (M) had an increased risk of diabetes: MGM Type I odds ratio (OR) 2.40 [95%CI: 1.07,5.38]; MGM Type II OR 1.61 [0.96,2.70]; M OR 1.95 [0.96,3.94] using self-reported questionnaire measures. These results were confirmed from maternal medical records which revealed an increased level of diabetes [OR 2.40 (1.16,4.96)] and an increased risk of repeated glycosuria during pregnancy [OR 1.60 (1.08,2.36)]. We tested numbers of FRAXA repeats and showed no such associations, indicating that the findings were not associated with triploid repeats in general. If these findings are replicated elsewhere, there are at least three possible interpretations: (i) maternal diabetes/prediabetes results in an increased number of FRAXE repeats; (ii) women with high numbers of FRAXE repeats are at increased risk of diabetes; or (iii) some common factor, e.g. genomic instability, results in both diabetes and increased repeats.

Does cross-generational epigenetic inheritance contribute to cultural continuity?

Human studies of cross-generational epigenetic inheritance have to consider confounding by social patterning down the generations, often referred to as 'cultural inheritance'. This raises the question to what extent is 'cultural inheritance' itself epigenetically mediated rather than just learnt. Human studies of non-genetic inheritance have demonstrated that, beyond foetal life, experiences occurring in mid-childhood before puberty are the most likely to be associated with cross-generational responses in the next generation(s). It is proposed that cultural continuity is played out along the axis, or 'payoff', between responsiveness and stability. During the formative years of childhood a stable family and/or home permits small children to explore and thereby learn. To counter disruptions to this family home ideal, cultural institutions such as local schools, religious centres and market places emerged to provide ongoing stability, holding the received wisdom of the past in an accessible state. This cultural support allows the growing child to freely indulge their responsiveness. Some of these prepubertal experiences induce epigenetic responses that also transfer molecular signals to the gametes through which they contribute to the conception of future offspring. In parallel co-evolution with growing cultural support for increasing responsiveness, 'runaway' responsiveness is countered by the positive selection of genetic variants that dampen responsiveness. Testing these ideas within longitudinal multigenerational cohorts will need information on ancestors/parents' own communities and experiences (Exposome scans) linked to ongoing Phenome scans on grandchildren; coupled with epigenome analysis, metastable epialleles and DNA methylation age. Interactions with genetic variants affecting responsiveness should help inform the broad hypothesis.

Beta2-adrenoceptor polymorphisms and asthma from childhood to middle age in the British 1958 birth cohort: a genetic association study.

BACKGROUND: Functionally relevant polymorphisms of the beta2-adrenoceptor gene (ADRB2) are common in white populations, but their contribution to the burden of airways disease in the population is uncertain. We aimed to relate the long-term prevalence of asthma or wheeze to functional coding region polymorphisms in the ADRB2 gene. METHODS: The British 1958 birth cohort consisted of all people born in Britain during a week in 1958. Asthma, wheezy bronchitis, and wheezing were ascertained by interview at ages 7, 11, 16, 23, 33, and 42 years, and lung function tests at 35 and 45 years. DNA samples from 8018 participants in the 45-year follow-up were genotyped for three coding variants in the ADRB2 gene. We extend the follow-up of this nationwide cohort by a further 10 years and relate asthma prevalence, prognosis, and lung function to functional coding region polymorphisms in the ADRB2 gene in the cohort members who contributed DNA samples. We also compared and combined our findings with those reaching significance in two previous meta-analyses. FINDINGS: Half the cohort (4105 of 8018) had some history of wheezing illness by age 42 years. Neither lifetime prevalence nor age at onset were related to ADRB2 coding variants. However, the common polymorphisms Arg16Gly (rs1042713, Arg 16 allele frequency 36.3%) and Gln27Glu (rs1042714, Glu 27 allele frequency 44.6%) were significantly associated with persistence of asthmatic symptoms from childhood to middle age. Among homozygotes for the Arg16-Gln27 haplotype at these loci, 19.3% (41 of 212) childhood wheezers had five or more wheezing episodes in the past year at age 42, compared with 11.9% (71 of 599) with no copy of this haplotype. However, only 3% of all frequent adult wheezing was statistically attributable to this haplotype. The less common Thr164Ile polymorphism (rs1800888, Ile allele frequency 1.5%) was not a major predictor of either frequency or prognosis of asthma. Our data do not support the findings of previous meta-analyses when considered in isolation or when combined with their contributory studies. INTERPRETATION: ADRB2 polymorphisms might predict a small component of the long-term prognosis in childhood asthma, but are not important determinants of asthma incidence or prevalence in the British population.

Sex-specific, male-line transgenerational responses in humans.

Transgenerational effects of maternal nutrition or other environmental 'exposures' are well recognised, but the possibility of exposure in the male influencing development and health in the next generation(s) is rarely considered. However, historical associations of longevity with paternal ancestors' food supply in the slow growth period (SGP) in mid childhood have been reported. Using the Avon Longitudinal Study of Parents and Children (ALSPAC), we identified 166 fathers who reported starting smoking before age 11 years and compared the growth of their offspring with those with a later paternal onset of smoking, after correcting for confounders. We analysed food supply effects on offspring and grandchild mortality risk ratios (RR) using 303 probands and their 1818 parents and grandparents from the 1890, 1905 and 1920 Overkalix cohorts, northern Sweden. After appropriate adjustment, early paternal smoking is associated with greater body mass index (BMI) at 9 years in sons, but not daughters. Sex-specific effects were also shown in the Overkalix data; paternal grandfather's food supply was only linked to the mortality RR of grandsons, while paternal grandmother's food supply was only associated with the granddaughters' mortality RR. These transgenerational effects were observed with exposure during the SGP (both grandparents) or fetal/infant life (grandmothers) but not during either grandparent's puberty. We conclude that sex-specific, male-line transgenerational responses exist in humans and hypothesise that these transmissions are mediated by the sex chromosomes, X and Y. Such responses add an entirely new dimension to the study of gene-environment interactions in development and health.

Maternal-fetal interactions and birth order influence insulin variable number of tandem repeats allele class associations with head size at birth and childhood weight gain.

Polymorphism of the insulin gene (INS) variable number of tandem repeats (VNTR; class I or class III alleles) locus has been associated with adult diseases and with birth size. Therefore, this variant is a potential contributory factor to the reported fetal origins of adult disease. In the population-based Avon Longitudinal Study of Pregnancy and Childhood birth cohort, we have confirmed in the present study the association between the INS VNTR III/III genotype and larger head circumference at birth (odds ratio [OR] 1.92, 95% CI 1.23-3.07; P = 0.004) and identified an association with higher cord blood IGF-II levels (P = 0.05 to 0.0001). The genotype association with head circumference was influenced by maternal parity (birth order): the III/III OR for larger head circumference was stronger in second and subsequent pregnancies (OR 5.0, 95% CI 2.2-11.5; P = 0.00003) than in first pregnancies (1.2, 0.6-2.2; P = 0.8; interaction with birth order, P = 0.02). During childhood, the III/III genotype remained associated with larger head circumference (P = 0.004) and was also associated with greater BMI (P = 0.03), waist circumference (P = 0.03), and higher fasting insulin levels in girls (P = 0.02). In addition, there were interactions between INS VNTR genotype and early postnatal weight gain in determining childhood BMI (P = 0.001 for interaction), weight (P = 0.005), and waist circumference (P = 0.0005), such that in the approximately 25% of children (n = 286) with rapid early postnatal weight gain, class III genotype-negative children among this group gained weight more rapidly. Our results indicate that complex prenatal and postnatal gene-maternal/fetal interactions influence size at birth and childhood risk factors for adult disease.

Common polymorphism in H19 associated with birthweight and cord blood IGF-II levels in humans.

BACKGROUND: Common genetic variation at genes that are imprinted and exclusively maternally expressed could explain the apparent maternal-specific inheritance of low birthweight reported in large family pedigrees. We identified ten single nucleotide polymorphisms (SNPs) in H19, and we genotyped three of these SNPs in families from the contemporary ALSPAC UK birth cohort (1,696 children, 822 mothers and 661 fathers) in order to explore associations with size at birth and cord blood IGF-II levels. RESULTS: Both offspring's and mother's H19 2992C>T SNP genotypes showed associations with offspring birthweight (P = 0.03 to P = 0.003) and mother's genotype was also associated with cord blood IGF-II levels (P = 0.0003 to P = 0.0001). The offspring genotype association with birthweight was independent of mother's genotype (P = 0.01 to P = 0.007). However, mother's untransmitted H19 2992T allele was also associated with larger birthweight (P = 0.04) and higher cord blood IGF-II levels (P = 0.002), suggesting a direct effect of mother's genotype on placental IGF-II expression and fetal growth. The association between mother's untransmitted allele and cord blood IGF-II levels was more apparent in offspring of first pregnancies than subsequent pregnancies (P-interaction = 0.03). Study of the independent Cambridge birth cohort with available DNA in mothers (N = 646) provided additional support for mother's H19 2992 genotype associations with birthweight (P = 0.04) and with mother's glucose levels (P = 0.01) in first pregnancies. CONCLUSION: The common H19 2992T allele, in the mother or offspring or both, may confer reduced fetal growth restraint, as indicated by associations with larger offspring birth size, higher cord blood IGF-II levels, and lower compensatory early postnatal catch-up weight gain, that are more evident among mother's smaller first-born infants.

Genetic variation in the type 2 insulin-like growth factor receptor gene and disparity in childhood height.

OBJECTIVE: The type 2 insulin-like growth factor receptor (IGF2R) is thought to regulate insulin-like growth factor-II (IGF-II) bioavailability by degrading it in the lysosomes after uptake. We hypothesised that polymorphisms in the IGF2R gene could alter size at birth and childhood growth. DESIGN AND METHODS: The hypothesis was tested in a normal birth cohort (Avon Longitudinal Study of Parents and Children) by genotyping the IGF2R gene gly1619arg polymorphism, which causes a non-conservative amino acid change in the IGF-II binding region, using PCR and restriction fragment length polymorphism analysis. RESULTS: The IGF2R gly1619arg genotype was not associated with any measure of size at birth, but A/A homozygotes grew more slowly, as determined by their change in height standard deviation scores (SDS) over the first three years (-0.70 (0.72); n = 12), than G/G homozygotes (0.00 (1.09); n = 561) (p = 0.03). They remained shorter during childhood and by the age of 7 years respective height SDS were: 0.73 (1.02) (n = 12) and 0.01 (0.99) (n = 634) (p = 0.01). These height differences persisted after adjusting for parental heights and gender. There were no detectable differences in weights at 7 years. CONCLUSION: Allelic variation in the gly1619arg SNP of the IGF2R gene is associated with disparity in childhood stature which could reflect altered binding of IGF-II to its receptor.

Male-line transgenerational responses in humans.

Genomic imprinting establishes the principle of epigenetic marks placed in one generation influencing gene expression in the next generation. This led to speculation that epigenetic gametic inheritance might underlie a form of transgenerational adaptation to major environmental challenges, such that exposures in one generation correlate with outcomes in the next generation(s). An ongoing collaboration between Umeå University, Sweden and the Avon Longitudinal Study of Parents and Childhood, Bristol University, UK has documented transgenerational correlations between food supply during the early life of the paternal grandparents and the grandchild's longevity, including associations with cardiovascular and diabetic deaths, and correlations between the onset of paternal smoking in mid-childhood and the body mass index of future sons. Whilst the mediating molecular mechanism(s) is unknown, the sex-specific transmission patterns and exposure-sensitive periods suggest a pre-evolved transgenerational response mechanism.

Association of the KIAA0319 dyslexia susceptibility gene with reading skills in the general population.

OBJECTIVE: The authors previously identified a haplotype on chromosome 6p22 defined by three single-nucleotide polymorphisms (SNPs) that was associated with dyslexia (reading disability) in two independent samples of families that included at least one sibling with severe reading impairment. The authors also showed that this haplotype is associated with a reduction in expression of the KIAA0319 gene. In addition, a completely independent study detected an association between KIAA0319 markers and reading disability. In the current study, the authors tested whether the KIAA0319 gene influences reading skills in the general population, rather than having an effect restricted to reading disability. METHOD: The authors genotyped four SNPs that previously showed association with reading disability in the population of 7-9-year-old children in the Avon Longitudinal Study of Parents and Children (ALSPAC), a large longitudinal cohort for which reading-related phenotypes were available for more than 6,000 individuals. The authors conducted quantitative analysis for both single markers and haplotypes. RESULTS: The rs2143340 SNP, which effectively tags the three-SNP risk haplotype, was significantly associated with a test for reading ability. The risk haplotype itself also showed association with poor reading performance, and as in previous research, the association was stronger when the analysis was controlled for IQ. CONCLUSIONS: These results both support a role of the KIAA0319 gene in the development of dyslexia and suggest that this gene influences reading ability in the general population. Moreover, the data implicate the three-SNP haplotype and its tagging SNP rs2143340 as genetic risk factors for poor reading performance.

Type 2 diabetes TCF7L2 risk genotypes alter birth weight: a study of 24,053 individuals.

The role of genes in normal birth-weight variation is poorly understood, and it has been suggested that the genetic component of fetal growth is small. Type 2 diabetes genes may influence birth weight through maternal genotype, by increasing maternal glycemia in pregnancy, or through fetal genotype, by altering fetal insulin secretion. We aimed to assess the role of the recently described type 2 diabetes gene TCF7L2 in birth weight. We genotyped the polymorphism rs7903146 in 15,709 individuals whose birth weight was available from six studies and in 8,344 mothers from three studies. Each fetal copy of the predisposing allele was associated with an 18-g (95% confidence interval [CI] 7-29 g) increase in birth weight (P=.001) and each maternal copy with a 30-g (95% CI 15-45 g) increase in offspring birth weight (P=2.8x10-5). Stratification by fetal genotype suggested that the association was driven by maternal genotype (31-g [95% CI 9-48 g] increase per allele; corrected P=.003). Analysis of diabetes-related traits in 10,314 nondiabetic individuals suggested the most likely mechanism is that the risk allele reduces maternal insulin secretion (disposition index reduced by ~0.15 standard deviation; P=1x10-4), which results in increased maternal glycemia in pregnancy and hence increased offspring birth weight. We combined information with the other common variant known to alter fetal growth, the -30G-->A polymorphism of glucokinase (rs1799884). The 4% of offspring born to mothers carrying three or four risk alleles were 119 g (95% CI 62-172 g) heavier than were the 32% born to mothers with none (for overall trend, P=2x10-7), comparable to the impact of maternal smoking during pregnancy. In conclusion, we have identified the first type 2 diabetes-susceptibility allele to be reproducibly associated with birth weight. Common gene variants can substantially influence normal birth-weight variation.

A common haplotype of the glucokinase gene alters fasting glucose and birth weight: association in six studies and population-genetics analyses.

Fasting glucose is associated with future risk of type 2 diabetes and ischemic heart disease and is tightly regulated despite considerable variation in quantity, type, and timing of food intake. In pregnancy, maternal fasting glucose concentration is an important determinant of offspring birth weight. The key determinant of fasting glucose is the enzyme glucokinase (GCK). Rare mutations of GCK cause fasting hyperglycemia and alter birth weight. The extent to which common variation of GCK explains normal variation of fasting glucose and birth weight is not known. We aimed to comprehensively define the role of variation of GCK in determination of fasting glucose and birth weight, using a tagging SNP (tSNP) approach and studying 19,806 subjects from six population-based studies. Using 22 tSNPs, we showed that the variant rs1799884 is associated with fasting glucose at all ages in the normal population and exceeded genomewide levels of significance (P=10-9). rs3757840 was also highly significantly associated with fasting glucose (P=8x10-7), but haplotype analysis revealed that this is explained by linkage disequilibrium (r2=0.2) with rs1799884. A maternal A allele at rs1799884 was associated with a 32-g (95% confidence interval 11-53 g) increase in offspring birth weight (P=.002). Genetic variation influencing birth weight may have conferred a selective advantage in human populations. We performed extensive population-genetics analyses to look for evidence of recent positive natural selection on patterns of GCK variation. However, we found no strong signature of positive selection. In conclusion, a comprehensive analysis of common variation of the glucokinase gene shows that this is the first gene to be reproducibly associated with fasting glucose and fetal growth.

Localization of a type 1 diabetes locus in the IL2RA/CD25 region by use of tag single-nucleotide polymorphisms.

As part of an ongoing search for genes associated with type 1 diabetes (T1D), a common autoimmune disease, we tested the biological candidate gene IL2RA (CD25), which encodes a subunit (IL-2R alpha) of the high-affinity interleukin-2 (IL-2) receptor complex. We employed a tag single-nucleotide polymorphism (tag SNP) approach in large T1D sample collections consisting of 7,457 cases and controls and 725 multiplex families. Tag SNPs were analyzed using a multilocus test to provide a regional test for association. We found strong statistical evidence in the case-control collection (P=6.5x10(-8)) for a T1D locus in the CD25 region of chromosome 10p15 and replicated the association in the family collection (P=7.3x10(-3); combined P=1.3x10(-10)). These results illustrate the utility of tag SNPs in a chromosome-regional test of disease association and justify future fine mapping of the causal variant in the region.

Investigation of UBE3A and MECP2 in Angelman syndrome (AS) and patients with features of AS.

Angelman syndrome (AS) is an imprinted neurobehavioral disorder characterized by mental retardation, absent speech, excessive laughter, seizures, ataxia, and a characteristic EEG pattern. Classical lesions, including deletion, paternal disomy, or epigenetic mutation, are confirmatory of AS diagnoses in 80% of cases. Loss-of-function mutations of the UBE3A gene have been identified in approximately 8% of AS cases, failing to account for the remaining patient population, and there appears to be a higher prevalence of mutations in familial than sporadic cases. We screened UBE3A in 45 index cases of AS without obvious 15q11-13 abnormalities. Pathological mutations were identified in 3/6 (50%) familial and 4/39 (>10%) sporadic cases. By combining our data with those of the literature, we demonstrate statistically that the frequency of UBE3A mutations is significantly higher in the familial than sporadic subsets of AS. This indicates that an independent molecular mechanism or 'phenocopy' exists for the sporadic group. Rett syndrome (RS), caused by mutations of the MECP2 gene, and patients with deletions of 22q13.3 --> qter, have overlapping clinical features with AS. We screened 24 of the sporadic AS cases without detectable UBE3A mutations for mutations of MECP2, but found none. A separate cohort of 43 atypical patients with features common to AS and RS, in whom 15q11-13 lesions and 22q13.3 --> qter deletion had been ruled out, were also screened for MECP2 mutations. One male patient was mosaic for a frameshift mutation of this gene (previously reported). While MECP2 mutations can cause a phenotype reminiscent of AS in rare cases, they fail to account for the excess of sporadic patients with a definitive clinical diagnosis of AS.

Hb F synthesis in sickle cell anaemia: a comparison of Saudi Arab cases with those of African origin

Fetal haemoglobin (Hb F) synthesis has been studied in 22 cases of sickle cell anaemia (SS) from Saudi Arabia and compared with an equal number of cases of African origin. Among the Saudi Arabs y chain synthesis ranged from 4.0 percent to 19.9 percent of the total non-x chain synthesis (mean 8.1 percent) while the corresponding range for the Negro cases was <0.3 percent to 4.6 percent (mean 1.7 percent). In both groups the peripheral blood HB F level was on average 3-4 times higher than the proportion synthesized, indicating that the selective survival of Hb F containing cells (F cells) was an important factor in determining the final Hb F levels. Among the Saudi Arab cases there was a significant negative correlation between the degree of F cell enrichment and either the Hb F level or the percentage y chain synthesis. No such correlation was observed among the Negro cases. A high proportion of the cases in both groups were carriers of x thalassaemia in addition to SS, but no effect of x talassaemia on Hb F production was observed (AU)