Towards a molecular epidemiology of alcohol dependence analysing the interplay of genetic and environmental risk factors

Background Progress in identifying genetic factors protective against alcohol dependence (AlcD) requires a paradigm shift in psychiatric epidemiology. Aims To integrate analysis of research into the genetics of alcoholism. Method Data from prospective questionnaire and interview surveys of the Australian twin panel, and from a subsample who underwent alcohol challenge, were analysed. Results In men, effects of alcohol dehydrogenase ADH2*1/*2 genotype or high alcohol sensitivity (risk-decreasing), and of history of childhood conduct disorder, or having monozygotic co-twin or twin sister with AlcD (risk-increasing) were significant and comparable in magnitude. Religious affiliation (Anglican versus other) was associated with the ADH2 genotype, but did not explain the associations with AlcD symptoms. No protective effect of the ADH2*1/*2 genotype was observed in women. Conclusions The early onset and strong familial aggregation of AlcD, and opportunity for within-family tests of genetic association to avoid confounding effects, make epidemiological family studies of adolescents and young adults and their families a priority.

Mechanisms of the inhibition of epithelial Na+ channels by CFTR and purinergic stimulation

The epithelial Na+ channel ENaC is inhibited when the cystic fibrosis transmembrane conductance regulator (CFTR) coexpressed in the same cell is activated by the cyclic adenosine monophosphate (cAMP)-dependent pathway. Regulation of ENaC by CFTR has been studied in detail in epithelial tissues from intestine and trachea and is also detected in renal cells. In the kidney, regulation of other membrane conductances might be the predominant function of CFTR. A similar inhibition of ENaC takes place when luminal purinergic receptors a re activated by 5 ' -adenosine triphosphate (ATP) or uridine triphosphate (UTP). Because both stimulation of purinergic receptors and activation of CFTR induce a Cl- conductance, it is likely that Cl- ions control ENaC activity.

Pharmacotherapy of the ion transport defect in cystic fibrosis

1. More than 1300 different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF), a disease characterized by deficient epithelial Cl- secretion and enhanced Na+ absorption. The clinical course of the disease is determined by the progressive lung disease. Thus, novel approaches in pharmacotherapy are based primarily on correction of the ion transport defect in the airways. 2. The current therapeutic strategies try to counteract the deficiency in Cl- secretion and the enhanced Na+ absorption. A number of compounds have been identified, such as genistein and xanthine derivatives, which directly activate mutant CFTR. Other compounds may activate alternative Ca2+-activated Cl- channels or basolateral K+ channels, which supply the driving force for Cl- secretion. Apart from that, Na+ channel blockers, such as phenamil and benzamil, are being explored, which counteract the hyperabsorption of NaCl in CF airways. 3. Clinical trials are under way using purinergic compounds such as the P2Y(2) receptor agonist INS365. Activation of P2Y(2) receptors has been found to both activate Cl- secretion and inhibit Na+ absorption. 4. The ultimate goal is to recover Cl- channel activity of mutant CFTR by either enhancing synthesis and expression of the protein or by activating silent CFTR Cl- channels. Strategies combining these drugs with compounds facilitating Cl- secretion and inhibiting Na+ absorption in vivo may have the best chance to counteract the ion transport defect in cystic fibrosis.

Expression and function of colonic epithelial K(v)LQT1 K+ channels

1. K(V)LQT1 (KCNQ1) is a voltage-gated K+ channel essential for repolarization of the heart action potential Defects in ion channels have been demonstrated in cardiac arrhythmia. This channel is inhibited potently by the chromanol 293B, The same compound has been shown to block cAMP-dependent electrolyte secretion in rat and human colon, Therefore, it was suggested that a K+ channel similar to K(V)LQT1 is expressed in the colonic epithelium. 2, In the present paper, expression of K(V)LQT1 and its function in colonic epithelial cells is described. Reverse transcription-polymerase chain reaction analysis of rat colonic mucosa demonstrated expression of K(V)LQT1 in both crypt cells and surface epithelium. When expressed in Xenopus oocytes, K(V)LQT1 induced a typical delayed activated K+ current. 3, As demonstrated, the channel activity could be further activated by increases in intracellular cAMP. These and other data support the concept that K(V)LQT1 is forming a component of the basolateral cAMP-activated Kf conductance in the colonic epithelium.

CFTR: Interacting with everything?

More than 1,300 different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) are the cause for cystic fibrosis. CFTR is in charge of proper secretion and absorption of electrolytes, and thus the disease is characterized by defective epithelial Cl– secretion and enhanced Na+ absorption. Recent studies show that CFTR interacts with other proteins via PDZ domains.

The cystic fibrosis transmembrane conductance regulator (CFTR) inhibits ENaC through an increase in the intracellular Cl- concentration

Activation of the CFTR Cl- channel inhibits epithelial Na+ channels (ENaC), according to studies on epithelial cells and overexpressing recombinant cells. Here we demonstrate that ENaC is inhibited during stimulation of the cystic fibrosis trans-membrance conductance regulator (CFTR) in Xenopus oocytes, independent of the experimental set-up and the magnitude of the whole-cell current. Inhibition of ENaC is augmented at higher CFTR Cl- currents. Similar to CFTR, ClC-0 Cl- currents also inhibit ENaC, as well as high extracellular Na+ and Cl- in partially permeabilized oocytes. Thus, inhibition of ENaC is not specific to CFTR and seems to be mediated by Cl-.

Underuse of beta-blockers following myocardial infarction: a tale of two cities

Aims: To measure factors associated with underuse of beta-blocker therapy after myocardial infarction (MI). Methods: The Newcastle and Perth collaborating centres of the World Health Organization (WHO) MONICA project (to MONItor trends and determinants of Cardiovascular disease) systematically evaluated all patients admitted to hospital in their respective regions with possible MI. A total of 1766 patients in Newcastle and 4503 patients in Perth, discharged from hospital after confirmed MI from 1985 to 1993, were studied, Rates of beta-blocker use before and after hospital discharge were evaluated and correlates of beta-blocker use determined. Results: Beta-blocker use was similar in Newcastle and Perth before MI (21% of patients in each centre). During hospital admission, beta-blocker therapy was initiated nearly twice as frequently in Perth compared with Newcastle (66 vs 36%, respectively) and more patients were discharged from hospital on beta-blockers in Perth (68%) than in Newcastle (45%). The main factors associated with underuse of beta-blockers in multivariate analysis were geographical centre (odds ratio (OR) for Newcastle compared with Perth 0.3 95% confidence interval (CI) 0.3-0.3), a history of previous MI (OR 0.6, 95% CI 0.5-0.7), admission to hospital in earlier years (OR 0.4, 95% CI 0.3-0.4 for years 1985-87 compared with years 1991-93), diabetes (OR 0.6, 95% CI 0.5-0.8) and the concomitant use of diuretics (OR 0.5, 95% CI 0.4-0.6) and calcium antagonists (OR 0.6, 95% CI 0.5-0.8). Conclusions: Underuse of beta-blockers after MI was strongly related to hospital prescribing patterns and not to community use of beta-blockers. Underuse occurred in patients with diabetes and in patients with left ventricular dysfunction, patients who stand to benefit most from beta-blocker use following MI.

Health services research using linked records: who consents and what is the gain?

Objective: To assess consent to record linkage, describe the characteristics of consenters and compare self-report versus Medicare records of general practitioner use. Method. Almost 40,000 women in the Australian Longitudinal Study on Women's Health were sent a request by mail for permission to link their Medicare records and survey data. Results: 19,700 women consented: 37% of young (18-23 years), 59% of mid-age (4550 years) and 53% of older women (70-75 years). Consenters tended to have higher levels of education and, among the older cohort, were in better health than nonconsenters. Women tended to under-report the number of visits to general practitioners. Conclusions: Record linkage of survey and Medicare data on a large scale is feasible. The linked data provide information on health and socio-economic status which are valuable for understanding health service utilisation. Implications: Linked records provide a powerful tool for health care research, particularly in longitudinal studies.

Human twinning is not linked to the region of chromosome 4 syntenic with the sheep twinning gene FecB

The tendency to dizygotic (DZ) twinning is inherited in both humans and sheep, and a fecundity gene in sheep (FecB) maps to sheep chromosome 6, syntenic with human 4q21-25. Our aim was to see whether a gene predisposing to human DZ twinning mapped to this region. DNA was collected from 169 pairs and 17 sets of 3 sisters (trios) from Australia and New Zealand who had each had spontaneous DZ twins, mostly before the age of 35, and from a replication sample of 111 families (92 affected sister pairs) from The Netherlands. Exclusion mapping was carried out after typing 26 markers on chromosome 4, of which 8 spanned the region Likely to contain the human homologue of the sheep FecB gene. We used nonparametric affected sib pair methods for linkage analysis [ASPEX 2.2, Hinds and Risch, 1999]. Complete exclusion of linkage (lod < -2) of a gene conferring a relative risk for sibs as low as 1.5 ((s) > 1.5) was obtained for all but the p terminus region on chromosome 4. Exclusion in the syntenic region was stronger, down to lambda (s) = 1.3. We concluded that if there is a gene influencing DZ twinning on chromosome 4, its effect must be minor. (C) 2001 Wiley-Liss, Inc.

Matching prescription claims with medication data for nursing home residents: Implications for prescriber feedback, drug utilisation studies and selection of prescription claims database

Medication data retrieved from Australian Repatriation Pharmaceutical Benefits Scheme (RPBS) claims for 44 veterans residing in nursing homes and Pharmaceutical Benefits Scheme (PBS) claims for 898 nursing home residents were compared with medication data from nursing home records to determine the optimal time interval for retrieving claims data and its validity. Optimal matching was achieved using 12 weeks of RPBS claims data, with 60% of medications in the RPBS claims located in nursing home administration records, and 78% of medications administered to nursing home residents identified in RPBS claims. In comparison, 48% of medications administered to nursing home residents could be found in 12 weeks of PBS data, and 56% of medications present in PBS claims could be matched with nursing home administration records. RPBS claims data was superior to PBS, due to the larger number of scheduled items available to veterans and the veteran's file number, which acts as a unique identifier. These findings should be taken into account when using prescription claims data for medication histories, prescriber feedback, drug utilisation, intervention or epidemiological studies. (C) 2001 Elsevier Science Inc. All rights reserved.

A comparison of family functioning, temperament, and childhood conditions in monozygotic twin pairs discordant for lifetime bulimia nervosa

Objective: The authors investigated differences between twins in nine pairs of female monozygotic twins in the Australian Twin Registry who were discordant for lifetime bulimia nervosa. Method: The twins affected and unaffected by lifetime bulimia nervosa were compared on self-report measures, including a measure of parental bonding, four measures of temperament, and six early-childhood medical conditions. Results: No twins had current bulimia nervosa, and there was no difference in weight or eating status between the affected and unaffected twins. The affected twins reported significantly lower self-esteem and less warmth but more overprotection by their mothers during childhood. Conclusions: Although limited by the small number of discordant twin pairs and the inability to detect causal relationships, these results suggest that environmental influences that promote low self-esteem may also increase the risk for bulimia nervosa. These temperamental differences may explain the discrepancies in parenting or perceived parenting.

An integrative approach for studying the etiology of alcoholism and other addictions

Studies of alcoholism etiology often focus on genetic or psy-chosocial approaches, but not both. Greater understanding of the etiology of alcohol, tobacco and other addictions will come from integration of these research traditions. A research approach is outlined to test three models for the etiology of addictions — behavioral undercontrol, pharmacologic vulnerability, negative affect regulation — addressing key questions including (i) mediators of genetic effects, (ii) genotype-environment correlation effects, (iii) genotype x environment interaction effects, (iv) the developmental unfolding of genetic and environmental effects, (v) subtyping including identification of distinct trajectories of substance involvement, (vi) identification of individual genes that contribute to risk, and (vii) the consequences of excessive use. By using coordinated research designs, including prospective assessment of adolescent twins and their siblings and parents; of adult substance dependent and control twins and their MZ and DZ cotwins, the spouses of these pairs, and their adolescent offspring; and of regular families; by selecting for gene-mapping approaches sibships screened for extreme concordance or discordance on quantitative indices of substance use; and by using experimental (drug challenge) as well as survey approaches, a number of key questions concerning addiction etiology can be addressed. We discuss complementary strengths and weaknesses of different sampling strategies, as well as methods to implement such an integrated approach illustrated for the study of alcoholism etiology. A coordinated program of twin and family studies will allow a comprehensive dissection of the interplay of genetic and environmental risk-factors in the etiology of alcoholism and other addictions.

IBD sharing around the PPARG locus is not increased in dizygotic twins or their mothers

We observe no evidence of linkage to the region around the PPARG locus in several samples of DZ twins who have been genotyped at multiple markers on chromosome 3 (Fig. 1). Among 199 Australian DZ twins ascertained for a history of wheezing2, mean identity by descent (IBD) sharing at the position of PPARG is 0.463 (99% bootstrapped confidence interval=0.412−0.516). We obtained a similar result with 232 pairs of Australian adolescent DZ twins taking part in a longitudinal study of naevus development3 (0.444, 0.390−0.499), and a set of 125 Australian adult DZ twin pairs assessed for anxiety4 (0.508, 0.435−0.580). A Dutch scan of 160 DZ twin pairs5 obtained slightly more encouraging results (0.553, 0.482−0.587, peak maximum lod score (MLS)=0.57). Pooling all these samples gives 0.477 (0.454−0.512) at the position of PPARG. The test for heterogeneity of sharing between studies was not significant (P=0.10). In the combined dataset, the peak IBD sharing (MLS=0.70) is 50 cM closer to the centromere than PPARG. Finally, in a sample of 203 Australian and New Zealand sister pairs where each had given birth to DZ twins6, sharing across the region is also not increased (0.433). We do not replicate linkage in the populations we study to survival of a twin pregnancy or polyovulation.