Effect of the BDNF V166M polymorphism on working memory in healthy adolescents.

Brain-derived neurotrophic factor (BDNF) may play a role in modulating memory function and there is growing evidence that the BDNF V166M polymorphism may influence episodic memory in humans. However, previous association studies examining this polymorphism and working memory are inconsistent. The current study examined this association in a large sample of adolescent twin-pairs and siblings (785 individuals from 439 families). A range of measures (event-related potential, general performance and reaction time) was obtained from a delayed-response working-memory task and total association was examined using the quantitative transmission disequilibrium tests (QTDT) program. Analyses had approximately 93-97% power (alpha= 0.05) to detect an association accounting for as little as 2% of the variance in the phenotypes examined. Results indicated that the BDNF V166M polymorphism is not associated with variation in working memory in healthy adolescents.

Genetic time-series analysis identifies a major QTL for in vivo alcohol metabolism not predicted by in vitro studies of structural protein polymorphism at the ADH1B or ADH1C loci.

After ingestion of a standardized dose of ethanol, alcohol concentrations were assessed, over 3.5 hours from blood (six readings) and breath (10 readings) in a sample of 412 MZ and DZ twins who took part in an Alcohol Challenge Twin Study (ACTS). Nearly all participants were subsequently genotyped on two polymorphic SNPs in the ADH1B and ADH1C loci known to affect in vitro ADH activity. In the DZ pairs, 14 microsatellite markers covering a 20.5 cM region on chromosome 4 that includes the ADH gene family were assessed, Variation in the timed series of autocorrelated blood and breath alcohol readings was studied using a bivariate simplex design. The contribution of a quantitative trait locus (QTL) or QTL's linked to the ADH region was estimated via a mixture of likelihoods weighted by identity-by-descent probabilities. The effects of allelic substitution at the ADH1B and ADH1C loci were estimated in the means part of the model simultaneously with the effects sex and age. There was a major contribution to variance in alcohol metabolism due to a QTL which accounted for about 64% of the additive genetic covariation common to both blood and breath alcohol readings at the first time point. No effects of the ADH1B*47His or ADH1C*349Ile alleles on in vivo metabolism were observed, although these have been shown to have major effects in vitro. This implies that there is a major determinant of variation for in vivo alcohol metabolism in the ADH region that is not accounted for by these polymorphisms. Earlier analyses of these data suggested that alcohol metabolism is related to drinking behavior and imply that this QTL may be protective against alcohol dependence.

Population genetic structure of the lettuce root aphid, Pemphigus bursarius (L.), in relation to geographic distance, gene flow and host plant usage.

Microsatellite markers were used to examine the population structure of Pemphigus bursarius, a cyclically parthenogenetic aphid. Substantial allele frequency differences were observed between populations on the primary host plant (collected shortly after sexual reproduction) separated by distances as low as 14 km. This suggested that migratory movements occur over relatively short distances in this species. However, the degree of allele frequency divergence between populations was not correlated with their geographical separation, indicating that isolation by distance was not the sole cause of spatial genetic structuring. Significant excesses of homozygotes were observed in several populations. Substantial allele frequency differences were also found between aphids on the primary host and those sampled from a secondary host plant after several parthenogenetic generations at the same location in two successive years. This could have been due to the existence of obligately parthenogenetic lineages living on the secondary host or genetically divergent populations confined to different secondary host plant species but sharing a common primary host.

Variation in alcohol pharmacokinetics as a risk factor for alcohol dependence.

BACKGROUND: The significant association between alcohol dehydrogenase (ADH)-2 genotype and alcohol-dependence risk, demonstrated in both Asian and non-Asian populations, suggests a link between the metabolism of alcohol (ethanol) and individual differences in susceptibility to dependence. METHODS: We tested this hypothesis by following up on subjects who took part in the Alcohol Challenge Twin Study conducted in 1979-1981 and comparing the blood and breath alcohol results in that study between subjects who subsequently did or did not meet diagnostic criteria for lifetime alcohol dependence in 1992-1993. RESULTS: Subjects who met DSM-III-R criteria for lifetime alcohol dependence at follow-up had higher blood and breath alcohol values after alcohol challenge than never-dependent subjects. Multivariate analysis showed independent effects of susceptibility to alcohol dependence and smoking status on blood alcohol concentrations, whereas habitual alcohol intake at the time of the initial study had marginally significant effects. The risk of alcohol dependence was 2-fold higher in men and 3-fold higher in women with blood or breath alcohol concentrations in the highest quartile than in the lowest quartile. CONCLUSIONS: In view of this association and the known genetic influences on both alcohol pharmacokinetics and alcohol dependence, it is probable that part of the heritability of dependence is mediated by genes (other than the known ADH2 and ADH3 polymorphisms) affecting alcohol metabolism.

Anxiety and depression in twin and sib pairs extremely discordant and concordant for neuroticism: prodromus to a linkage study.

Multivariate modelling of anxiety and depression data in twins has suggested that the two phenotypes are largely underpinned by one genetic factor, while other studies have indicated a relationship between these disorders and the neuroticism personality trait. As part of a study to identify quantitative trait loci for anxiety and depression, questionnaire responses and interviews of 15,027 Australian twins and 11,389 of their family members conducted during the past 20 years were reviewed to identify individuals with neuroticism, anxiety and depression scores in the upper or lower deciles of the population. This information was then used to identify extreme discordant and concordant (EDAC) sib pairs. 1373 high-scoring and 1571 low-scoring subjects (2357 sib pairs) were selected for participation, and extremely high participation rates were achieved, with over 90% of contactable prospective participants completing the interview phase, and over 90% of these providing blood or buccal samples. Participation bias arising from the nature of the selection variables was minimal, with only a small difference between rates of interview participation among prospective participants with high and low selection scores (89.4% vs 91.6%). The interview permitted the diagnosis of depression and several anxiety disorders (OCD, agoraphobia, panic disorder, generalised anxiety disorder) in this sample according to DSM-IV criteria. The methodology for selection of prospective subjects was demonstrated to be extremely successful, with highly significant differences in depression and anxiety disorder prevalence rates between individuals in the two selection groups. The success of this EDAC sampling scheme will enhance the power for QTL linkage and association analysis in this sample.

Observations on the effects of low frequency electromagnetic fields on cellular transcription in Drosophila larvae reared in field-free conditions.

Drosophila larvae reared inside a micro-metal box with an internal field strength 0.004 microT, were treated with a magnetic field of 50 Hz, 8 microT. for 20 min. Control experienced 0.004 microT. Cellular transcript levels were assessed using slot blots and quantified using a Phosphorimager. Blots were hybridised using probes against HSP 70a, Histone 1.9, and Copia. The low frequency EMFs very significantly decreased transcript levels, indicating that experimental responses may be influenced by previous exposure or lack of previous exposure.

Molecular biology of alcohol dependence, a complex polygenic disorder.

Alcohol dependence, and the medical conditions which arise from prolonged excessive alcohol use, have no single cause. Like other complex diseases, they result from a combination of social, personal and genetic contributions; but within any society genetic variation has a substantial influence on individual risk. The genes presently known to affect alcohol dependence produce variation in alcohol metabolism; other genes which affect personality or susceptibility to intoxication are likely to be significant but so far reproducible evidence is scanty. Designs which include related subjects have advantages for the study of complex diseases, because any association effects can be placed in the context of overall heritability and because linkage analysis can also be included. Examples of our studies of alcohol metabolism, consumption and dependence are presented.

MN blood group affects response of serum LDL cholesterol level to a low fat diet.

Previous studies found that MZ twin pairs who are blood group NN have greater intrapair variability in plasma lipid levels than those who are MM or MN. This led to the prediction that the response of plasma lipid levels to a low fat diet would depend on MN blood group, the greatest response being in those who are NN. The present study was based upon 254 patients who took part in the Australian Polyp Prevention Project. This was a 2 x 2 x 2 randomised factorial design based upon the presence or absence of the three factors: a dietary fibre supplement, a beta-carotene supplement and reduced intake of dietary fat. The lowering of plasma, low density lipoprotein (LDL) cholesterol, in response to a low fat diet was greatest in those who were NN and least in MN heterozygotes. Overall, a reduction in LDL level was observed in the 47% of the APPP population who were on a low fat diet and who were homozygous MM or NN. The result was consistent with a balanced polymorphism at or near the GLYA locus on chromosome 4 that influences the sensitivity of plasma lipid levels to dietary fluctuations in fat intake.

Study of Alu sequences at the hypoxanthine phosphoribosyltransferase (hprt) encoding region of man.

The hypoxanthine phosphoribosyltransferase (hprt) encoding region of man is considered rich in Alu sequences: with 49 sequences present within 57 kilobases. Subfamily classification of the Alu sequences and identification of flanking direct repeats has been carried out to detect past rearrangements associated with their insertion into the region. Members of the Alu-J and three Alu-S subfamilies are present, along with the existence of free left arm sequences. Using available data, a comparison is made of the Alu subfamilies present at different gene regions. The heterogeneity in the number of each subfamily present at different genes shows that no one particular subfamily attained saturation in the genome. Several adjacent insertions of Alu sequences are seen at the hprt region. Furthermore two novel sequences are described, there is an incident where one Alu sequence has inserted into the middle poly(A) tract of an existing sequence at the hprt region; while another result from an Alu/Alu cross-over event elsewhere in the genome, before insertion into the hprt region. Once inserted, the Alu sequences are rarely subject to loss or rearrangement.

Southern analysis reveals a large deletion at the hypoxanthine phosphoribosyltransferase locus in a patient with Lesch-Nyhan syndrome.

Whole genomic hprt clones were used in Southern analysis to screen the integrity of the hprt gene in a family that includes a patient with HPRT enzyme deficiency causal to Lesch-Nyhan syndrome. A 5 kb DNA sequence deletion was found to have its endpoints in the first and third introns. The probes identified the carrier status of female family members, aided by an RFLP carried by the mother's normal X-chromosome.

Molecular variation of the human elastin (ELN) gene in a normal human population.

DNA sequence diversity in the human elastin genomic region has been estimated by RFLP analysis in a normal human population. The proportion of polymorphic nucleotides and the degree of nucleotide diversity were 0.0034 and 0.0018 respectively. It is argued that the estimate of nucleotide diversity does not indicate strong purifying selection in the region. A total of 144 restriction sites were sampled in each of 80 independent chromosomes representing the screening of 58080 bp overall. Six main haplotypes were constructed; they represent at least 84% of the 80 chromosomes sampled. Analysis for linkage disequilibrium revealed two statistically significant comparisons out of 54 tests, approximately the proportion that would be statistically significant at the 5% level by chance. A higher order quadrigenic disequilibrium was detected. The relationship between the physical distance separating polymorphic restriction sites and linkage disequilibrium is discussed. The development of elastin haplotypes and knowledge of the pattern of linkage disequilibrium should aid the study of elastin related disease and human evolution.

Investigation of natural genetic variation in the circadian system of Drosophila melanogaster. II. Biometrical analyses of locomotor activity rhythms recorded in constant darkness.

The locomotor activity rhythms of 24 isochromosomal strains of Drosophila melanogaster were recorded in constant conditions, using an experimental design suitable for the serial screening with so many strains using limited equipment. The data obtained were subjected to biometrical genetic analysis. The results show that four characteristics of the rhythms (period, phase, definition, and waveform) display genetically based variation in expression and that each appears to be affected by a range of genes.

Histone H4 acetylated at lysine 16 and proteins of the Drosophila dosage compensation pathway co-localize on the male X chromosome through mitosis.

In the fruit fly Drosophila, dosage compensation involves several proteins acting in concert to double the transcriptional activity of genes on the single male X chromosome. Three of these proteins, MLE, MSL-1 and histone H4 acetylated at lysine 16 (H4Ac16), have recently been shown to be located almost exclusively on the male X chromosome in interphase (polytene) cells. We show here that in neuroblasts from third instar Drosophila larvae antisera to H4Ac16, MLE and MSL-1 uniquely label the distal, euchromatic region of the male X chromosome through mitosis. The centromere-proximal, heterochromatic region of the male X is not labelled with these antisera, nor are male autosomes or any chromosomes in female cells. That the association of H4Ac16 with the male X chromosome persists, even when the chromosome is maximally compacted and transcriptionally quiescent, argues that this modified histone is an integral component of the dosage compensation pathway. In the nuclei of interphase neuroblasts from male (but never female) larvae, antibodies to H4Ac16 revealed a small, brightly labelled patch against a background of generally weak nuclear staining. In double-labelling experiments, this patch was also labelled, albeit comparatively weakly, with antibodies to MSL-1. These results strongly suggest that the distal, euchromatic region of the X chromosome in male cells occupies a limited and relatively compact nuclear domain.

An investigation of natural genetic variation in the circadian system of Drosophila melanogaster: rhythm characteristics and methods of quantification.

Variation in four characteristics of the circadian locomotor activity rhythm was investigated in 24 true-breeding strains of Drosophila melanogaster with a view to establishing methods of phenotypic measurement sufficiently robust to allow subsequent biometric analysis. Between them, these strains formed a representative sample of the genetic variability of a natural population. Period, phase, definition (the degree to which a rhythmic signal was obscured by noise), and rhythm waveform were all found to vary continuously among the strains, although within each strain the rhythm phenotype was remarkably consistent. Each characteristic was found to be sufficiently robust to permit objective measurement using several different methods of quantification, which were then compared.

Two new polymorphisms in the human elastin gene (ELN).

Two polymorphisms in the human elastin gene have been detected, one with RsaI and a second with BamHI.

Exclusion of an elastin gene (ELN) mutation as the cause of pseudoxanthoma elasticum (PXE) in one family.

An intragenic elastin Hinf I polymorphism has been used to study the inheritance of elastin alleles in a family considered to show recessive inheritance of pseudoxanthoma elasticum (PXE). The marker has proved informative, excluding the elastin gene as a cause of PXE in this family. In addition, whole genomic human elastin clones were used in Southern analysis to screen the family for gross elastin gene rearrangements, but none were detected.

Histone H4 isoforms acetylated at specific lysine residues define individual chromosomes and chromatin domains in Drosophila polytene nuclei.

Histone H4 isoforms acetylated at lysines 5, 8, 12, or 16 have been shown, by indirect immunofluorescence with site-specific antisera, to have distinct patterns of distribution in interphase, polytene chromosomes from Drosophila larvae. H4 molecules acetylated at lysines 5 or 8 are distributed in overlapping, but nonidentical, islands throughout the euchromatic chromosome arms. beta-Heterochromatin in the chromocenter is depleted in these isoforms, but relatively enriched in H4 acetylated at lysine 12. H4 acetylated at lysine 16 is found at numerous sites along the transcriptionally hyperactive X chromosome in male larvae, but not in male autosomes or any chromosome in female cells. These findings support the hypothesis that H4 molecules acetylated at particular sites mediate unique and specific effects on chromatin function.