Apolipoprotein E genotype predicts 24-month bayley scales infant development score

APOE genotype is associated with left-handedness and visuospatial skills in children

We sought to investigate whether apolipoprotein E (APOE) genotype is associated with unique profiles of cognitive functioning during early-life. School-aged children (N=147) received standardized achievement tests, the Rey-Osterrieth Complex Figure Test (Copy Condition; RCFT-CC), assessment of hand dominance for writing, and buccal swab testing to determine their APOE genotype. Significant differences were found on the RCFT-CC, with epsilon 2-positive children performing worse on this measure relative to both epsilon 3/3 (p=0.032) and epsilon 4-positive children (p=0.018). Further, a higher prevalence of left-hand dominance for writing was observed among epsilon 2-positive children (29.2%) relative to epsilon 3/3 (8.9%) and epsilon 4-positive children (6.1%; p=0.012), although this finding did not account for the observed group differences on the RCFT-CC. Findings raise the possibility that in childhood, the epsilon 2 allele may be associated with: (a) decreased functioning in certain cognitive domains; (b) factors associated with atypical hemispheric dominance. Results may be consistent with the theory of antagonistic pleiotropy, which suggests that APOE may have different protective effects at different developmental stages.

Revision of the apolipoprotein E compensatory mechanism recruitment hypothesis

The association between the apolipoprotein E epsilon4 allele and Alzheimer's disease (AD) is well-established. Functional neuroimaging research has supported a compensatory mechanism recruitment hypothesis whereby nondemented epsilon4 participants use additional cognitive resources to buffer against episodic memory declines in older age, a mechanism that is presumably associated with encroaching disease. However, recent studies have implicated a beneficial effect associated with the epsilon4 allele early in the life span. These studies suggest a revised hypothesis whereby epsilon4 persons perform better on cognitive measures early in the life span and then show greater recruitment of brain regions during performance to compensate for declines in older age caused by preclinical AD.

Very low lead exposures and children's neurodevelopment

PURPOSE OF REVIEW

We remain far from achieving the goal of eliminating lead-associated neurodevelopmental morbidities in children. New evidence regarding the blood lead levels at which morbidities occur have led to calls for the Centers for Disease Control and Prevention to reduce the current screening guideline of 10 microg/dl. The review evaluates the basis for these calls.

RECENT FINDINGS

Adverse outcomes, such as reduced intelligence quotient and academic deficits, occur at levels below 10 microg/dl. Some studies suggest that the rate of decline in performance is greater at levels below 10 microg/dl than above 10 microg/dl, although a plausible mechanism has not been identified. Increased exposure is also associated with neuropsychiatric disorders such as attention deficit hyperactivity disorder and antisocial behavior. Functional imaging studies are beginning to provide insight into the neural substrate of lead's neurodevelopmental effects. Current protocols for chelation therapy appear ineffective in preventing such effects, although environmental enrichment might do so.

SUMMARY

No level of lead exposure appears to be 'safe' and even the current 'low' levels of exposure in children are associated with neurodevelopmental deficits. Primary prevention of exposure provides the best hope of mitigating the impact of this preventable disease.

Late neurodevelopmental effects of early exposures to chemical contaminants: reducing uncertainty in epidemiological studies

Early exposures to environmental chemicals are reliably associated with late neurotoxicities in children. However, substantial scatter of observations exists around the estimated dose-effect relationships. This variability has many potential sources, one of which is interindividual differences in susceptibility. Such differences imply that the long-term impacts of exposure will not the same for all individuals, but will vary depending on a variety of factors that might either aggravate or mitigate contaminant effects. These include co-exposures, genetic polymorphisms and characteristics of the social environment. The context dependence of contaminant effects has implications both for study designs and analytical approaches. In addition, a systems approach to understanding the associations among contaminant exposures, covariates and health outcomes is necessary.

Adverse birth outcome among mothers with low serum cholesterol

OBJECTIVE

The objective of this study was to assess whether low maternal serum cholesterol during pregnancy is associated with preterm delivery, impaired fetal growth, or congenital anomalies in women without identified major risk factors for adverse pregnancy outcome.

METHODS

Mother-infant pairs were retrospectively ascertained from among a cohort of 9938 women who were referred to South Carolina prenatal clinics for routine second-trimester serum screening. Banked sera were assayed for total cholesterol; <10th percentile of assayed values (159 mg/dL at mean gestational age of 17.6 weeks) defined a "low total cholesterol" prenatal risk category. Eligible women were aged 21 to 34 years and nonsmoking and did not have diabetes; neonates were liveborn after singleton gestations. Total cholesterol values of eligible mothers were adjusted for gestational age at screening before risk group assignment. The study population included 118 women with low total cholesterol and 940 women with higher total cholesterol. Primary analyses used multivariate regression models to compare rates of preterm delivery, fetal growth parameters, and congenital anomalies between women with low total cholesterol and control subjects with mid-total cholesterol values >10th percentile but <90th percentile.

RESULTS

Prevalence of preterm delivery among mothers with low total cholesterol was 12.7%, compared with 5.0% among control subjects with mid-total cholesterol. The association of low maternal serum cholesterol with preterm birth was observed only among white mothers. Term infants of mothers with low total cholesterol weighed on average 150 g less than those who were born to control mothers. A trend of increased microcephaly risk among neonates of mothers with low total cholesterol was found. Low maternal serum cholesterol was unassociated with risk for congenital anomalies.

CONCLUSIONS

Total serum cholesterol <10th population percentile was strongly associated with preterm delivery among otherwise low-risk white mothers in this pilot study population. Term infants of mothers with low total cholesterol weighed less than control infants among both racial groups.

Lead neurotoxicity in children: decomposing the variability in dose-effect relationships

BACKGROUND

Enormous progress has been made in recent decades in our understanding of lead neurotoxicology in children, but an important obstacle to additional progress is the striking variability that is evident in any plot of a lead biomarker versus a health endpoint.

METHODS

In this article, three potential sources of variability are identified: (1) errors or imprecision in characterizing dose (and/or outcome); (2) incomplete characterization of endpoint variance attributable to factors other than lead; and (3) inter-individual differences in susceptibility to lead neurotoxicity.

RESULTS

Strategies are suggested for reducing the variability contributed by these sources, including the development of validated PBPK models and biomarkers of early biological effects; the development of more comprehensive models of outcome variance and, specifically, the application of multi-level models that incorporate supra-individual and supra-family risk factors; and the use of study designs that permit assessments of the effect modifying influence of contextual factors on the form and severity of neurotoxicity.

CONCLUSION

Decomposing the variability in the distribution of observed scores around the best-fit lines that describe the dose-effect relationships for lead neurotoxicity in children is a major research need.

Neurodevelopment in Seizure-prone and Seizure-resistant Rat Strains: Recognizing Conflicts in Management

Cytoarchitectural alterations during central nervous system (CNS) development are believed to underlie aberrations in brain morphology that lead to epilepsy. We have recently reported marked reductions in hippocampal and white matter volumes along with relative ventriculomegaly in a rat strain bred to be seizure-prone (FAST) compared to a strain bred to be seizure-resistant (SLOW) (Gilby et al., 2002, American Epilepsy Society 56th Annual Meeting). This study was designed to investigate deviations in gene expression during late-phase embryogenesis within the brains of FAST and SLOW rats. In this way, we hoped to identify molecular mechanisms operating differentially during neurodevelopment that might ultimately create the observed differences in brain morphology and/or seizure susceptibility. Using Superarray technology, we compared the expression level of 112 genes, known to play a role in neurodevelopment, within whole brains of embryonic day 21 (E21) FAST and SLOW rats. Results revealed that while most genes investigated showed near equivalent expression levels, both Apolipoprotein E (APOE) and the beta2 subunit of the voltage-gated sodium channel (SCN2beta) were significantly underexpressed in brains of the seizure-prone embryos. Currently, these transcripts have no known interactions during embryogenesis; however, they have both been independently linked to seizure disposition and/or neurodevelopmental aberrations leading to epilepsy. Thus, alterations in the timing and/or degree of expression for APOE and SCN2beta may be important to developmental cascades that ultimately give rise to the differing brain morphologies, behaviors, and/or seizure vulnerabilities that characterize these strains.

The contribution of apolipoprotein E alleles on cognitive performance and dynamic neural activity over six decades

Neuroimaging shows brain-functional differences due to apolipoprotein E (APOE) polymorphisms may exist decades before the increased risk period for Alzheimer's disease, but little is known about their effect on cognition and brain function in children and young adults. This study assessed 415 healthy epsilon2 and epsilon4 carriers and matched epsilon3/epsilon3 controls, spanning ages 6-65, on a range of cognitive tests. Subjects were also compared on a new dynamical measure of EEG activity during a visual working memory task using alphabetical stimuli. epsilon4 subjects had better verbal fluency compared to epsilon3, an effect that was strongest in 51-65 year-olds. No epsilon4 deficits in cognition were found. In 6-15 year-olds, there were differences in total spatio-temporal wave activity between epsilon3 and epsilon4 subjects in the theta band, approximately 200ms post-stimulus. Differences in brain function in younger epsilon4 subjects and superior verbal fluency across the entire age range suggest that the APOE epsilon4 allele is an example of antagonistic pleiotropy.

Association of apolipoprotein E genotype and cerebral palsy in children

OBJECTIVES

We tested the hypotheses that apolipoprotein E genotype, in particular carriage of the epsilon4 allele, is more likely to be associated with cerebral palsy and that children with more severe neurologic impairment are more likely to carry this allele.

METHODS

In this cross-sectional study, 209 children with cerebral palsy were matched with healthy control subjects according to gender and race. Diagnosis of cerebral palsy was confirmed through physician consultation, medical chart review, and parent interview. Apolipoprotein E genotyping was performed with DNA obtained with buccal swabs. Severity of motor impairment was rated by physical therapists, and occipitofrontal circumference was measured.

RESULTS

Compared with gender- and race-matched control subjects, overall risk for cerebral palsy was elevated 3.4-fold among children carrying an epsilon4 allele and was particularly elevated for children with quadriplegia/triplegia. This finding was independent of birth weight. Carriage of the epsilon4 allele was also associated with increased severity of cerebral palsy and with a trend toward increased likelihood for microcephaly. Moreover, children carrying an epsilon2 allele were at greater risk for cerebral palsy.

CONCLUSIONS

These data implicate the apolipoprotein E epsilon4 and epsilon2 genotypes as susceptibility factors in determining neurologic outcomes after perinatal brain injury. Additional studies are warranted to establish the role of apolipoprotein E in specific pathogenetic pathways leading to cerebral palsy or poor neurologic outcomes after perinatal brain injury.

Role of apolipoprotein E4 in protecting children against early childhood diarrhea outcomes and implications for later development

Our group and others have reported a series of studies showing that heavy burdens of diarrheal diseases in the formative first two years of life in children in urban shantytowns have profound consequences of impaired physical and cognitive development lasting into later childhood and schooling. Based on these previous studies showing that apolipoprotein E4 (APOE4) is relatively common in favela children, we review recent data suggesting a protective role for the APOE4 allele in the cognitive and physical development of children with heavy burdens of diarrhea in early childhood. Despite being a marker for cognitive decline with Alzheimer's and cardiovascular diseases later in life, APOE4 appears to be important for cognitive development under the stress of heavy diarrhea. The reviewed findings provide a potential explanation for the survival advantage in evolution of the thrifty APOE4 allele and raise questions about its implications for human development under life-style changes and environmental challenges.

Parallel deficits in linear growth and mental development in low-income Mexican infants in the second year of life

OBJECTIVE

To explore anthropometric indicators and mental development in very-low-income children in the second year of life.

DESIGN

Cross-sectional survey.

SETTING

Low-income areas (income <20th percentile) in semi-urban Mexico (defined as towns or cities with 2,500-50,000 inhabitants).

SUBJECTS

Eight hundred and ninety-six children aged 12.5-23.5 months surveyed from September to December 2001.

METHODS

Questionnaire survey and anthropometric survey of households. Multivariate regression models evaluated differences across age in anthropometry (height-for-age Z-score (HAZ) and weight-for-height Z-score) and cognitive function (Mental Development Index (MDI) of the Bayley Scales of Infant Development) while controlling for socio-economic and parental characteristics.

RESULTS

There was a significant decline in HAZ and in age-adjusted MDI score across the second year of life. Although the children showed MDI scores close to the mean, normed US values at 13-14 months, the scores were significantly lower than expected in older children (P < 0.0001), even after controlling for socio-economic status and parental characteristics. At 13-14 months, only 3% of children received scores below 70 (less than minus two standard deviations), whereas by 19-20 months, almost 17% of children were performing below this level. No socio-economic or parental characteristics were significant predictors of HAZ or MDI.

CONCLUSIONS

Parallel deficits are evident in both height-for-age and cognitive functioning during the second year of life in low-income Mexican infants. The consistency of these growth and development findings further stresses the need for targeted interventions to reduce the vulnerability of low-income Mexican children very early in life.

The distribution of apolipoprotein E alleles in Scottish perinatal deaths

BACKGROUND

The apolipoprotein E (ApoE) polymorphism has been well studied in the adult human population, in part because the e4 allele is a known risk factor for Alzheimer's disease. Little is known of the distribution of ApoE alleles in newborns, and their association with perinatal brain damage has not been investigated.

METHODS

ApoE genotyping was undertaken in a Scottish cohort of perinatal deaths (n = 261), some of whom had prenatal brain damage. The distribution of ApoE alleles in perinatal deaths was compared with that in healthy liveborn infants and in adults in Scotland.

RESULTS

ApoE e2 was over-represented in 251 perinatal deaths (13% v 8% in healthy newborns, odds ratio (OR) = 1.63, 95% confidence interval (CI) 1.13 to 2.36 and 13% v 8% in adults, OR = 1.67, 95% CI 1.16 to 2.41), both in liveborn and stillborn perinatal deaths. In contrast, the prevalence of ApoE e4 was raised in healthy liveborn infants (19%) compared with stillbirths (13%, OR = 1.59, 95% CI 1.11 to 2.26) and with adults (15%, OR = 1.35, 95% CI 1.04 to 1.76). However, no correlation was found between ApoE genotype and the presence or absence of perinatal brain damage.

CONCLUSIONS

This study shows a shift in ApoE allelic distribution in early life compared with adults. The raised prevalence of ApoE e2 associated with perinatal death suggests that this allele is detrimental to pregnancy outcome, whereas ApoE e4 may be less so. However, ApoE genotype did not appear to influence the vulnerability for perinatal hypoxic/ischaemic brain damage, in agreement with findings in adult brains and in animal models.

Distribution of apolipoprotein E alleles in a Scottish healthy newborn population

The different alleles of the human apolipoprotein E polymorphism, ApoE epsilon2, epsilon3, epsilon4, have important implications for systemic lipid metabolism, immunological function and for the brain in maintenance and in response to injury. Few studies have focussed on their role in early life. The ApoE alleles and genotypes were ascertained in the cord blood of 371 full-term and normal Scottish newborn infants using PCR methodology. The results were compared to previously published data for Scottish adults in late middle age. There was a marginally significant over-representation of epsilon4 and under-representation of epsilon3 alleles in healthy infants as compared with adults. Inspection of the individual genotypes confirms the over-representation of ApoE 4/4 and 2/4 with a reduction in ApoE 2/3 and 3/3 when compared with Scottish adults. Although these results may have occurred by chance, the ApoE epsilon4 allele may confer an increased risk of premature death.

APOE4 protects the cognitive development in children with heavy diarrhea burdens in Northeast Brazil

Polymorphisms in the apolipoprotein E (APOE) have constituted the major rationale to identify potential risk groups for developing late-onset Alzheimer's disease and help to predict recovery of cognitive function after brain injury. However, the APOE impact on cognitive development in children living in poor areas of the developing world, where we have discovered profound significant associations of early childhood diarrhea (at 0-2 y) with lasting impairments of growth, cognition, and school performance, is not known. Therefore, we conducted APOE genotyping in 72 Brazilian shantytown children under active surveillance since birth, using purified DNA extracted from buccal cell samples. We found a high frequency of APOE4 alleles (18% versus 9-11% expected) in children with lower diarrhea burdens. When we examined the children who experienced the heavier diarrhea burdens (greater than or equal to the median of seven illnesses in the first 2 y of life), those with APOE4 did significantly better in the coding subtest (p=0.01) when compared with APOE4-negative children with similar diarrhea burdens. Positive correlations between the APOE4 occurrence and coding scores remained, even after adjusting for family income, maternal education, and breast-feeding. Moreover, the APOE4-positive group, under heavy burdens of diarrhea, had preserved semantic fluency and the mean difference in fluency scores, p=0.025, a standardized coefficient for disproportional verbal fluency impairment. Our findings show that APOE4 is relatively common in favela children and suggest a protective role of the APOE4 allele in children with a history of heavy burdens of diarrhea in their first 2 y of life.