Genetic variation, β-blockers, and perioperative myocardial infarction

Remodelers of the vascular microenvironment: The effect of biopolymeric hydrogels on vascular diseases

Vascular disease is the leading health problem worldwide. Vascular microenvironment encompasses diverse cell types, including those within the vascular wall, blood cells, stromal cells, and immune cells. Initiation of the inflammatory state of the vascular microenvironment and changes in its mechanics can profoundly affect vascular homeostasis. Biomedical materials play a crucial role in modern medicine, hydrogels, characterized by their high-water content, have been increasingly utilized as a three-dimensional interaction network. In recent times, the remarkable progress in utilizing hydrogels and understanding vascular microenvironment have enabled the treatment of vascular diseases. In this review, we give an emphasis on the utilization of hydrogels and their advantages in the various vascular diseases including atherosclerosis, aneurysm, vascular ulcers of the lower limbs and myocardial infarction. Further, we highlight the importance and advantages of hydrogels as artificial microenvironments.

The role of plasma concentrations and drug characteristics of beta-blockers in fall risk of older persons

Beta-blocker usage is inconsistently associated with increased fall risk in the literature. However, due to age-related changes and interindividual heterogeneity in pharmacokinetics and dynamics, it is difficult to predict which older adults are more at risk for falls. Therefore, we wanted to explore whether elevated plasma concentrations of selective and nonselective beta-blockers are associated with an increased risk of falls in older beta-blocker users. To answer our research question, we analyzed samples of selective (metoprolol, n = 316) and nonselective beta-blockers (sotalol, timolol, propranolol, and carvedilol, n = 179) users from the B-PROOF cohort. The associations between the beta-blocker concentration and time to first fall were assessed using Cox proportional hazard models. Change of concentration over time in relation to fall risk was assessed with logistic regression models. Models were adjusted for potential confounders. Our results showed that above the median concentration of metoprolol was associated with an increased fall risk (HR 1.55 [1.11-2.16], p = .01). No association was found for nonselective beta-blocker concentrations. Also, changes in concentration over time were not associated with increased fall risk. To conclude, metoprolol plasma concentrations were associated with an increased risk of falls in metoprolol users while no associations were found for nonselective beta-blockers users. This might be caused by a decreased β1-selectivity in high plasma concentrations. In the future, beta-blocker concentrations could potentially help clinicians estimate fall risk in older beta-blockers users and personalize treatment.

Excessively High Chronic Propranolol Overdose in Infantile Hemangioma: A Case Report

BACKGROUND Infantile hemangiomas are the most common benign tumors of childhood, occurring in approximately 5% of infants. Oral propranolol at 2 to 3 mg/kg daily is recommended for systemic treatment of high-risk infantile hemangiomas. Multiple propranolol formulations exist, and propranolol overdose can occur due to improper patient counseling. Propranolol acute toxicity in the pediatric population and its management are well described in the literature. However, data are lacking on chronic propranolol overdose and how to manage it, with the awareness that abrupt discontinuation of therapeutic doses of propranolol can lead to rebound sinus tachycardia. CASE REPORT A 7-month-old girl was prescribed a therapeutic dose of propranolol (1 mg/kg/day) to treat infantile hemangioma. However, due to an administration error, the patient received approximately 8 times the recommended dose (7.6 mg/kg/day for 2 months, then increased to 15.5 mg/kg/day for 2 weeks) and, surprisingly, remained asymptomatic. Her electrocardiogram was normal, and all routine laboratory tests were within the reference range. Propranolol was successfully tapered over 3 weeks by reducing the dose by 50% weekly until it reached the therapeutic dose. After tapering, the patient was asymptomatic, with a mild increase in hemangioma size. After 6 weeks of the therapeutic dose, the hemangioma was fading away. CONCLUSIONS This case is one of the few cases reported in the literature of high, chronic propranolol overdose in pediatric patients. The patient remained asymptomatic, and the overdose was successfully managed with gradual tapering over several weeks. This case report can serve as a guide in managing subsequent cases.

Complications in spinal tumor surgery (review of literature)

Combined anterior and posterior approaches are required in spinal tumor surgery and considered highly invasive. Anatomical and physiological features of the surgical intervention area should be taken into consideration as well. Thus, these criteria reflect the severity of intraoperative complications during the surgical treatment of spinal tumors. The authors reviewed the scientific literature on the frequency and nature of complications in surgical interventions for spinal tumors.The most significant risk factors for intraoperative complications have been considered, the main of which are: the proximity of the location of the main vessels and viscera, the development of postoperative liquorrhea, as well as surgical site infection. Based on the studied information, we presented the methods of prevention and surgical tactics options in complications.

Perioperative Precision Medicine: Where Are We in 2020?

PURPOSE OF REVIEW

The present review examines how targeted approaches to care, based on individual variability in patient characteristics, could be applied in the perioperative setting. Such an approach would enhance individualized risk assessment and allow for targeted preventive and therapeutic decision-making in patients at increased risk for adverse perioperative events.

RECENT FINDINGS

Prior and current studies highlight valuable lessons on how future investigations attempting to link specific patient-related characteristics or treatment modalities with outcomes and adverse drug responses might be designed in the perioperative setting.

SUMMARY

Our review highlights the past, present, and future directions of perioperative precision medicine. Current evidence provides important lessons on how a specific patient and disease tailored approach can help perioperative physicians in delivering the most appropriate and safest perioperative care.

Correlation of CYP2D6 allelic polymorphism to outcome of acute coronary syndrome in mid-Euphrates Iraqi patients on metoprolol therapy

This study aims to investigate the different clinically relevant allele variants (allele frequencies) of CYP2D6 gene and to determine whether a specific genotype of CYP2D6 gene (based on genetic polymorphism "allelic types" and combination) have impact on metoprolol effectiveness (clinical outcome) in patients who have acute coronary syndrome (ACS). The study included 250 patients with ACS who were classified into 2 study groups, 125 patients received metoprolol and served as a study group (Group1) and 125 who received no metoprolol therapy (due to contraindication to the medication) and served as a control group (Group 2). Venous blood samples were taken from all participants for DNA extraction. Urine samples were also collected to assess the metabolic ratio using High-performance liquid chromatography (HPLC) technique. There was significant variation in the distribution of Iraqi patients with respect to CYP2D6 allelic polymorphism as compared to similar patients in other countries. Besides, this significant difference existed in patients' outcome in terms of morbidity and mortality in respect to variable genotypes and phenotypes. We recommend a dose individualization of metoprolol in patients with ACS is essential to improve patients' outcome.

Efficacy and safety of nicorandil on perioperative myocardial injury in patients undergoing elective percutaneous coronary intervention: results of the PENMIPCI trial

Background

Previous studies have indicated that nicorandil can reduce perioperative myocardial injury (PMI) in patients undergoing elective percutaneous coronary intervention (ePCI), but this conclusion is still controversial. Additionally, studies reporting on the safety of nicorandil are lacking. Therefore, we performed this prospective study to evaluate the efficacy and safety of nicorandil on PMI in patients undergoing ePCI.

Methods

One hundred and forty-six patients with coronary heart disease (CHD) scheduled to undergo ePCI were randomly assigned to the nicorandil group (n=74) or control group (n=72). The primary outcomes were the change in cardiac troponin T (cTnT) and creatine kinase-MB (CK-MB) at 12 and 24 hours after surgery. The secondary outcome was the incidence of major adverse cardiac events (MACE), which was a composite of cardiac death, nonfatal myocardial infarction, new heart failure or coronary revascularization.

Results

There was no difference in age (54.76±5.93 vs 56.35±5.22) between the nicorandil group and the control group. In addition, no differences were observed in the cTnT and CK-MB levels between the two groups at admission (all P⩾0.05). Compared with those in the control group, the cTnT (0.15±0.12 vs 0.12±0.10 at 12 hours and 0.17±0.12 vs 0.13±0.10 at 24 hours) and CK-MB (15.35±8.23 vs 12.31±7.93 at 12 hours and 13.63±8.87 vs 11.13±5.71 at 24 hours) levels in the nicorandil group were significantly decreased after surgery (all P⩽0.05). Furthermore, nicorandil did not increase the incidence of MACE in the nicorandil group compared with the control group (12.16% vs 12.50%).

Conclusions

Nicorandil can reduce PMI in patients undergoing ePCI and does not increase the incidence of MACE.

Clinical Trial Registration

URL: http://www.chictr.org.cn/. Unique Identifier: ChiCTR-IOR-17012056.

Recent developments and future directions for the use of pharmacogenomics in cardiovascular disease treatments

INTRODUCTION

Cardiovascular disease is still the leading cause of death worldwide. There are many environmental and genetic factors that play a role in the development of cardiovascular disease. The treatment of cardiovascular disease is beginning to move in the direction of personalized medicine by using biomarkers from the patient's genome to design more effective treatment plans. Pharmacogenomics have already uncovered many links between genetic variation and response of many different drugs. Areas covered: This article will focus on the main polymorphisms that impact the risk of adverse effects and response efficacy of statins, clopidogrel, aspirin, β-blockers, warfarin dalcetrapib and vitamin E. The genes discussed include SLCO1B1, ABCB1, CYP3A4, CYP3A5, CYP2C19, PTGS1, PTGS2, ADRB1, ADCY9, CYP2C19, PON1, CES1, PEAR1, GPIIIa, CYP2D6, CKORC1, CYP2C9 and Hp. Expert opinion: Although there are some convincing results that have already been incorporated in the labelling treatment guidelines, most gene-drug relationships have been inconsistent. A better understanding of the relationships between genetic factors and drug response will provide more opportunities for personalized diagnosis and treatment of cardiovascular disease.

Improving Prediction of Postoperative Myocardial Infarction With High-Sensitivity Cardiac Troponin T and NT-proBNP

BACKGROUND

This study sought to determine whether preoperatively measured high-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP) improve cardiac risk prediction in patients undergoing major noncardiac surgery compared with the standard risk indices.

METHODS

In this ancillary study to the Vitamins in Nitrous Oxide trial, patients were included who had preoperative hs-cTnT and NT-proBNP measured (n = 572). Study outcome was the incidence of postoperative myocardial infarction (MI) within the first 3 postoperative days. hs-cTnT was considered elevated if >14 ng/L and NT-proBNP if >300 ng/L. Additional cutoff values were investigated on the basis of receiver operating characteristic statistics. Biomarker risk prediction was compared with Lee's Revised Cardiac Risk Index (RCRI) with the use of standard methods and net reclassification index.

RESULTS

The addition of hs-cTnT (>14 ng/L) and NT-proBNP (>300 ng/L) to RCRI significantly improved the prediction of postoperative MI (event rate 30/572 [5.2%], Area under the receiver operating characteristic curve increased from 0.590 to 0.716 with a 0.66 net reclassification index [95% confidence interval 0.32-0.99], P < .001). The use of 108 ng/L as a cutoff for NT-proBNP improved sensitivity compared with 300 ng/L (0.87 vs 0.53). Sensitivity, specificity, positive, and negative predictive value for hs-cTnT were 0.70, 0.60, 0.09, and 0.97 and for NT-proBNP were 0.53, 0.68, 0.08, and 0.96.

CONCLUSIONS

The addition of cardiac biomarkers hs-cTnT and NT-proBNP to RCRI improves the prediction of adverse cardiac events in the immediate postoperative period after major noncardiac surgery. The high negative predictive value of preoperative hs-cTnT and NT-proBNP suggest usefulness as a "rule-out" test to confirm low risk of postoperative MI.

Longitudinal data analysis for rare variants detection with penalized quadratic inference function

Longitudinal genetic data provide more information regarding genetic effects over time compared with cross-sectional data. Coupled with next-generation sequencing technologies, it becomes reality to identify important genes containing both rare and common variants in a longitudinal design. In this work, we adopted a weighted sum statistic (WSS) to collapse multiple variants in a gene region to form a gene score. When multiple genes in a pathway were considered together, a penalized longitudinal model under the quadratic inference function (QIF) framework was applied for efficient gene selection. We evaluated the estimation accuracy and model selection performance under different model settings, then applied the method to a real dataset from the Genetic Analysis Workshop 18 (GAW18). Compared with the unpenalized QIF method, the penalized QIF (pQIF) method achieved better estimation accuracy and higher selection efficiency. The pQIF remained optimal even when the working correlation structure was mis-specified. The real data analysis identified one important gene, angiotensin II receptor type 1 (AGTR1), in the Ca2+/AT-IIR/α-AR signaling pathway. The estimated effect implied that AGTR1 may have a protective effect for hypertension. Our pQIF method provides a general tool for longitudinal sequencing studies involving large numbers of genetic variants.

Pharmacogenetics in obstetric anesthesia

The 21st century has been billed as the era of "precision/personalized medicine." Genetic investigation of clinical syndromes may guide therapy as well as reveal previously unknown biological or pharmacological pathways that may result in novel drug therapies. Several clinical issues in obstetrics and obstetric anesthesiology have been targets for genetic investigations. These include evaluation of the genetic effects on preterm labor and the progression of labor, spinal anesthesia-induced hypotension and the response to medications used to treat hypotension, and the effect of gene variants on pain and analgesic responses. Most studies have examined specific single nucleotide polymorphisms. Findings have revealed modest effects of genetic variation without tangible impact on current clinical practice. Over the next decade, increased availability of whole exome and genome sequencing, epigenetics, large genetic databases, computational biology and other information technology, and more rapid methods of real-time genotyping may increase the impact of genetics in the clinical arena of obstetrics and obstetric anesthesia.

The Gly16 Allele of the Gly16Arg Single-Nucleotide Polymorphism in the β₂-Adrenergic Receptor Gene Augments Perioperative Use of Vasopressors: A Retrospective Cohort Study

BACKGROUND

Arterial hypotension is frequent in patients undergoing anesthesia and may aggravate the outcome. Common genetic variations may influence the cardiovascular response to anesthesia. In this retrospective cohort study, we tested whether variation in the gene encoding the β2-adrenergic receptor (ADRB2) influences perioperative arterial blood pressure and consequently the use of vasopressors.

METHODS

Five hundred seventy-one Danish Caucasians undergoing neurosurgery were genotyped for 5 marker single-nucleotide polymorphisms (SNPs) within ADRB2 (Gly16Arg, Gln27Glu, Thr164Ile, Arg175Arg, and Gly351Gly). A pairwise tagging principle was used to identify ADRB2 haplotypes. Mean arterial blood pressure (MAP) was recorded in the supine awake state and, together with administration of vasopressors (ephedrine and/or phenylephrine), for 30 minutes after induction of general anesthesia (sevoflurane/remifentanil or propofol/remifentanil).

RESULTS

Four hundred thirteen (72%) patients received ephedrine and/or phenylephrine. Only baseline MAP (P < 0.001) and the Arg175Arg SNP (P = 0.01) were associated with nadir perioperative MAP. The Gly16Arg SNP but no other SNPs showed a trend toward an association with the amount of vasopressors used during anesthesia with Arg16 homozygotes receiving less ephedrine equivalents. The Arg16-Gln27-Thr164-Arg175-Gly351 haplotype was associated with approximately 13% lower vasopressor requirements than the most common Gly16-Glu27-Thr164-Arg175-Gly351 haplotype (P = 0.01).

CONCLUSIONS

Gly16 carriers received larger amounts of vasopressor compared with Arg16 homozygotes. This corresponds to previous studies demonstrating that the Gly16 allele in ADRB2 is associated with vasodilation and high cardiac output.

Factors affecting the development of adverse drug reactions to β-blockers in hospitalized cardiac patient population

The aim of the present study was to undertake a study on the prevalence of cytochrome P450 2D6 (CYP2D6) poor metabolizer alleles (*3, *4, *5, and *6) on a Montenegrin population and its impact on developing adverse drug reactions (ADRs) of β-blockers in a hospitalized cardiac patient population. A prospective study was conducted in the Cardiology Center of the Clinical Center of Montenegro and included 138 patients who had received any β-blocker in their therapy. ADRs were collected using a specially designed questionnaire, based on the symptom list and any signs that could point to eventual ADRs. Data from patients' medical charts, laboratory tests, and other available parameters were observed and combined with the data from the questionnaire. ADRs to β-blockers were observed in 15 (10.9%) patients. There was a statistically significant difference in the frequency of ADRs in relation to genetically determined enzymatic activity (P<0.001), with ADRs' occurrence significantly correlating with slower CYP2D6 metabolism. Our study showed that the adverse reactions to β-blockers could be predicted by the length of hospitalization, CYP2D6 poor metabolizer phenotype, and the concomitant use of other CYP2D6-metabolizing drugs. Therefore, in hospitalized patients with polypharmacy CYP2D6 genotyping might be useful in detecting those at risk of ADRs.

Sympathetic autonomic dysfunction and impaired cardiovascular performance in higher risk surgical patients: implications for perioperative sympatholysis

Objective

Recent perioperative trials have highlighted the urgent need for a better understanding of why sympatholytic drugs intended to reduce myocardial injury are paradoxically associated with harm (stroke, myocardial infarction). We hypothesised that following a standardised autonomic challenge, a subset of patients may demonstrate excessive sympathetic activation which is associated with exercise-induced ischaemia and impaired cardiac output.

Methods

Heart rate rise during unloaded pedalling (zero workload) prior to the onset of cardiopulmonary exercise testing (CPET) was measured in 2 observation cohorts of elective surgical patients. The primary outcome was exercise-evoked, ECG-defined ischaemia (>1 mm depression; lead II) associated with an exaggerated increase in heart rate (EHRR ≥12 bpm based on prognostic data for all-cause cardiac death in preceding epidemiological studies). Secondary outcomes included cardiopulmonary performance (oxygen pulse (surrogate for left ventricular stroke volume), peak oxygen consumption (VO_2peak), anaerobic threshold (AT)) and perioperative heart rate.

Results

EHRR was present in 40.4–42.7% in both centres (n=232, n=586 patients). Patients with EHRR had higher heart rates perioperatively (p<0.05). Significant ST segment depression during CPET was more common in EHRR patients (relative risk 1.7 (95% CI 1.3 to 2.1); p<0.001). EHRR was associated with 11% (95%CI 7% to 15%) lower predicted oxygen pulse (p<0.0001), consistent with impaired left ventricular function.

Conclusions

EHRR is common and associated with ECG-defined ischaemia and impaired cardiac performance. Perioperative sympatholysis may further detrimentally affect cardiac output in patients with this phenotype.

GNAS gene variants affect β-blocker-related survival after coronary artery bypass grafting

BACKGROUND

Cardiac overexpression of the β-adrenoreceptor (βAR)-coupled stimulatory G-protein subunit Gαs enhances inotropic responses to adrenergic stimulation and improves survival in mice under βAR blockade. The authors recently identified three common haplotypes in the GNAS gene encoding Gαs, with the greatest Gαs protein expression and signal transduction in haplotype *3 carriers and less in haplotype *2 and *1 carriers. The authors tested the hypothesis that these GNAS variants result in altered mortality in patients after coronary artery bypass graft surgery, particularly in those receiving βAR blockade.

METHODS

This prospective analysis included 1,627 European ancestry patients undergoing primary coronary artery bypass graft surgery. Patients were genotyped for two GNAS haplotype tagging single-nucleotide polymorphisms defining three major haplotypes. Up to 5-yr all-cause mortality was estimated using a Cox proportional hazard model; hazard ratios and 95% CIs were calculated while adjusting for demographics, clinical covariates, and the new EuroSCORE II.

RESULTS

Univariate analysis revealed haplotype-dependent 5-yr mortality rates (*1/*1: 18.9%, *2/*1: 13.7%, *2/*2: 9.3%, *3/*1: 10.6%, *3/*2: 9.1%, and *3/*3: 9.6%; P = 0.0006). After adjustment for other predictors of death, homozygote haplotype *1 carriers showed a doubled risk for death (hazard ratio, 2.2; 95% CI, 1.2 to 3.8; P = 0.006). Considering only patients receiving βAR blockers (n = 1,267), the adjusted risk of death even tripled (hazard ratio, 3.0; 95% CI, 1.5 to 6.1; P = 0.002).

CONCLUSIONS

GNAS haplotypes independently associate with an increased risk of death after primary coronary artery bypass graft surgery. These results are most pronounced in patients receiving βAR blockers, strengthening the rationale for personalized treatment, to decrease medication side effects and improve outcomes.

Genetic variation in the β1-adrenergic receptor is associated with the risk of atrial fibrillation after cardiac surgery

BACKGROUND

Postoperative atrial fibrillation (PoAF) after cardiac surgery is common and associated with increased morbidity and mortality. Increased sympathetic activation after surgery contributes to PoAF, and β-blockers are the first-line recommendation for its prevention. We examined the hypothesis that common functional genetic variants in the β1-adrenoreceptor, the mediator of cardiac sympathetic activation and drug target of β-blockers, are associated with the risk for PoAF and with the protective effect of β-blockers.

METHODS

In a prospective cohort study, we studied 947 adult European Americans who underwent cardiac surgery at Vanderbilt University between 1999 and 2005. We genotyped 2 variants in the β1-adrenoreceptor, rs1801253 (Arg389Gly) and rs1801252 (Ser49Gly), and used logistic regression to examine the association between genotypes and PoAF occurring within 14 days after surgery, before and after adjustment for demographic and clinical covariates.

RESULTS

Postoperative atrial fibrillation occurred in 239 patients (25.2%) and was associated with rs1801253 genotype (adjusted P = .008), with Gly389Gly having an odds ratio of 2.63 (95% CI 1.42-4.89) for PoAF compared to the common Arg389Arg (P = .002). In a predefined subgroup analysis, this association appeared to be stronger among patients without β-blocker prophylaxis (adjusted odds ratio 7.00, 95% CI 1.82-26.96, P = .005) compared to patients with β-blocker prophylaxis, among whom the association between rs1801253 genotype and PoAF was not statistically significant (adjusted P = .11).

CONCLUSION

The Gly389 variant in the β1-adrenoreceptor is associated with PoAF, and this association appears to be modulated by β-blocker therapy. Future studies of the association of other adrenergic pathway genes with PoAF will be of interest.

Genetic contributions to labor pain and progress

Studies on genetic contributions to labor analgesia have essentially evaluated the μ-opioid receptor gene (OPRM1), with some evidence that p.118A/G of OPRM1 influences the response to neuraxial opioids. As for labor progress, the β2-adrenergic receptor gene (ADRB2) is associated with preterm labor and delivery, and impacts the course of labor. Taken together though, there is no evidence that pharmacogenetic testing is needed or beneficial in the context of obstetric anesthesia; however, realizing the influence of genetic variants on specific phenotypes provides the rationale for a more cautious interpretation of clinical studies that attempt to find a dose-regimen that fits all.

A meta-analysis of CYP2D6 metabolizer phenotype and metoprolol pharmacokinetics

Metoprolol, a commonly prescribed beta-blocker, is primarily metabolized by cytochrome P450 2D6 (CYP2D6), an enzyme with substantial genetic heterogeneity. Several smaller studies have shown that metoprolol pharmacokinetics is influenced by CYP2D6 genotype and metabolizer phenotype. To increase robustness of metoprolol pharmacokinetic estimates, a systematic review and meta-analysis of pharmacokinetic studies that administered a single oral dose of immediate release metoprolol was performed. Pooled analysis (n= 264) demonstrated differences in peak plasma metoprolol concentration, area under the concentration-time curve, elimination half-life, and apparent oral clearance that were 2.3-, 4.9-, 2.3-, and 5.9-fold between extensive and poor metabolizers, respectively, and 5.3-, 13-, 2.6-, and 15-fold between ultra-rapid and poor metabolizers (all p<0.001). Enantiomer-specific analysis revealed genotype-dependent enantio-selective metabolism, with nearly 40% greater R- vs S-metoprolol metabolism in ultra-rapid and extensive metabolizers. This study demonstrates a marked effect of CYP2D6 metabolizer phenotype on metoprolol pharmacokinetics and confirms enantiomer specific metabolism of metoprolol.

Genetics and epigenetics in perioperative medicine

PURPOSE OF REVIEW

To summarize is to review recent progress in 'genomic' science and how this may be applied to the perioperative environment. Although investigations that relate genetic variation to perioperative outcomes continue, it is increasingly apparent that epigenetic mechanisms may contribute to much of the observed variation in complex outcomes not otherwise explained by differences in genetic sequence.

RECENT FINDINGS

Examples of recent findings relating to the role of epigenetic modifications in complex disease and outcomes are derived from research into type 1 diabetes, pain, and the hypoxic response. These studies provide models for future cohort study design, potential perioperative drug targets, and hypothesis development. Genetic and epigenetic factors combine to alter both gene expression and drug responses at both pharmacokinetic and pharmacodynamic levels. These factors impact on the efficacy and safety of multiple drug classes used in perioperative medicine.

SUMMARY

Enhancing our understanding of the way in which patients as genomic organisms interact with the perioperative environment requires a more sophisticated appreciation of the factors governing gene expression than has been the case to date. Epigenetic mechanisms are sure to play a pivotal role in what is essentially an acquired phenotype.