Genetics in eating disorders: state of the science

Intellectual function in patients with anorexia nervosa and bulimia nervosa

OBJECTIVE

This study aimed to examine cognitive function in individuals with anorexia nervosa (AN) and bulimia nervosa (BN) on the basis of IQ measures, indexes and subtests of the Wechsler Adult Intelligence Scale – Third Edition (WAIS-III).

METHODS

A total of 41 patients with AN, 40 patients with BN and 40 healthy controls (HC), matched for sex, age and education, were recruited consecutively to complete the WAIS-III.

RESULTS

The AN group showed a significantly lower performance than the HC group on most global measures and on eight of the 13 administered subtests. Minor differences in verbal function were detected between the BN group and the HC group.

CONCLUSION

The patients with eating disorders showed normal intellectual functions compared with the normative population. However, the AN group displayed a consistently lower performance than the matched HC group, which performed above normative means. The BN group performed at a level between that of the AN and HC groups.

Eating Disorders: From Twin Studies to Candidate Genes and Beyond

Substantial effort has been put into the exploration of the biological background of eating disorders, through family, twin and molecular genetic studies. Family studies have shown that anorexia (AN) and bulimia nervosa (BN) are strongly familial, and that familial etiologic factors appear to be shared by both disorders. Twin studies often focus on broader phenotypes or subthreshold eating disorders. These studies consistently yielded moderate to substantial heritabilities. In addition, there has been a proliferation of molecular genetic studies that focused on Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) AN and BN. Seven linkage regions have been identified in genome-wide screens. Many genetic association studies have been performed, but no consistent association between a candidate gene and AN or BN has been reported. Larger genetic association studies and collaborations are needed to examine the involvement of several candidate genes and biological pathways in eating disorders. In addition, twin studies should be designed to assist the molecular work by further exploring genetic determinants of endophenotypes, evaluating the magnitude of contribution to liability of measured genotypes as well as environmental risk factors related to eating disorders. In this manner twin and molecular studies can move the field forward in a mutually informative way.

Eating disorders: progress and challenges

BACKGROUND

Eating disorders are common health problems afflicting mainly female adolescents and young women. They are associated with important physical health and psychosocial morbidity, and carry increased risk of death. Their cause is not yet completely understood and their management is complex, with some patients resisting all available treatments. AIMS OF THIS REVIEW: To provide the readers with an update regarding our knowledge and understanding of eating disorders.

METHODS

Medline database has been used for searching articles on eating disorders published since 1980. The key words used were eating disorders, anorexia nervosa, bulimia nervosa, bulimia, and binge eating. Professional books published during this period has been also reviewed.

CONCLUSIONS

In the last 30 years a substantial improvement has been achieved both in the understanding and management of eating disorders, but many problems still need to be resolved. Three principal priorities should be addressed. First, the actual classification of eating disorders should be revised, since about half the cases seen in clinical practice receive a diagnosis of eating disorder not otherwise specified, and it is common to observe a migration between eating disorder diagnoses. Second, the research on pathogenesis should better clarify the exact role of genetic and environmental risk factors, and how they interact and vary across the development and maintenance of eating disorders. Third, there is an urgent need both to disseminate the few evidence-based treatments available, and to develop more potent treatments for all the eating disorder diagnostic categories.

Anorexia nervosa: towards an integrative neuroscience model

We reviewed the evidence for emotion-related disturbances in anorexia nervosa (AN) from behavioural, cognitive, biological and genetic domains of study. These domains were brought together within the framework of an integrative neuroscience model that emphasizes the role of emotion and feeling and their regulation, in brain organization. PsychInfo and Medline searches were performed to identify published peer-reviewed papers on AN within each domain. This review revealed evidence for 'Emotion', 'Thinking and Feeling' and 'Self-regulation' disturbances in AN that span non-conscious to conscious processes. An integrative neuroscience framework was then applied to develop a model of AN, from which hypotheses for empirical investigation are generated. We propose that AN reflects a core disturbance in emotion at the earliest time stage of information processing with subsequent effects on the later stages of thinking, feeling and self-regulation.

Genetic and environmental influences on disordered eating: An adoption study

Twin studies indicate significant genetic, but little shared environmental, influences on eating disorders. However, critics argue that study limitations constrain the conclusions that can be drawn. Adoption studies avoid many of these limitations, but to date, no adoption studies of eating pathology have been conducted. The current study was the first adoption study to examine genetic/environmental effects for disordered eating. Participants included 123 adopted and 56 biological female sibling pairs. Disordered eating (i.e., overall eating pathology, body dissatisfaction, weight preoccupation, binge eating) was assessed with the Minnesota Eating Behaviors Survey (Klump, McGue, & Iacono, 2000; von Ranson, Klump, Iacono, & McGue, 2005). Biometric model fitting indicated significant genetic influences (59%-82%) on all forms of disordered eating, with nonshared environmental factors accounting for the remaining variance. Shared environmental factors did not contribute significantly to any disordered eating symptom. Our findings bolster those from twin studies and provide critical evidence of significant genetic effects on disordered eating symptoms.

Blood levels of brain-derived neurotrophic factor correlate with several psychopathological symptoms in anorexia nervosa patients

BACKGROUND

Evidence of a role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of eating disorders (ED) has been provided by association studies and by murine models. BDNF plasma levels have been found altered in ED and in psychiatric disorders that show comorbidity with ED.

AIMS

Since the role of BDNF levels in ED-related psychopathological symptoms has not been tested, we investigated the correlation of BDNF plasma levels with the Symptom Checklist 90 Revised (SCL-90R) questionnaire in a total of 78 ED patients.

METHODS

BDNF levels, measured by the enzyme-linked immunoassay system, and SCL-90R questionnaire, were assessed in a total of 78 ED patients. The relationship between BDNF levels and SCL-90R scales was calculated using a general linear model.

RESULTS

BDNF plasma levels correlated with the Global Severity Index and the Positive Symptom Distress Index global scales and five of the nine subscales in the anorexia nervosa patients. BDNF plasma levels were able to explain, in the case of the Psychoticism subscale, up to 17% of the variability (p = 0.006).

CONCLUSION

Our data suggest that BDNF levels could be involved in the severity of the disease through the modulation of psychopathological traits that are associated with the ED phenotype.

Schmidt M, Poustka F. Psychiatrische Erkrankungen bei Verwandten von Patienten mit Anorexia nervosa und Bulimia nervosa

Zusammenfassung: Fragestellung: Im deutschen Raum gibt es kaum Familienuntersuchungen von Patienten mit Anorexia und Bulimia nervosa. Methodik: In einer Multizenter Studie wurde das Auftreten psychiatrischer Erkrankungen bei Familienangehörigen 1., 2. und 3. Grades von 65 anorektischen (n = 746) und 21 bulimischen Patienten (n = 265) mit denen von 37 gesunden Kontrollen (n = 480) sowie 11 depressiven Patienten (n = 157) verglichen. Messinstrumente waren u.a. das Diagnostische Interview für Genetische Studien bzw. das Familien Interview für Genetische Studien. Ergebnisse: Die Prävalenz von Anorexia nervosa (signifikant) sowie von depressiven Störungen (Trend) war bei Verwandten 1. und 2. Grades von Patienten mit Essstörungen gegenüber der gesunden Gruppe erhöht. Die meisten Ergebnisse waren eher bei den Familien bulimischer Patienten ausgeprägt. Die Prävalenzraten für psychiatrische Erkrankungen waren insgesamt prozentual niedriger als in vergleichbaren US amerikanischen Stichproben. Schlussfolgerung: Die Ergebnisse könnten für eine familiäre Vulnerabilität bzw. genetisches Risiko von Patienten mit Anorexia und Bulimia nervosa sprechen. Der Zusammenhang des niedrigen Alters der Indexpatienten auf die geringeren Prävalenzraten wird diskutiert.

Altered brain-derived neurotrophic factor blood levels and gene variability are associated with anorexia and bulimia

Murine models and association studies in eating disorder (ED) patients have shown a role for the brain-derived neurotrophic factor (BDNF) in eating behavior. Some studies have shown association of BDNF -270C/T single-nucleotide polymorphism (SNP) with bulimia nervosa (BN), while BDNF Val66Met variant has been shown to be associated with both BN and anorexia nervosa (AN). To further test the role of this neurotrophin in humans, we screened 36 SNPs in the BDNF gene and tested for their association with ED and plasma BDNF levels as a quantitative trait. We performed a family-based association study in 106 ED nuclear families and analyzed BDNF blood levels in 110 ED patients and in 50 sib pairs discordant for ED. The rs7124442T/rs11030102C/rs11030119G haplotype was found associated with high BDNF levels (mean BDNF TCG haplotype carriers = 43.6 ng/ml vs. mean others 23.0 ng/ml, P = 0.016) and BN (Z = 2.64; P recessive = 0.008), and the rs7934165A/270T haplotype was associated with AN (Z =-2.64; P additive = 0.008). The comparison of BDNF levels in 50 ED discordant sib pairs showed elevated plasma BDNF levels for the ED group (mean controls = 41.0 vs. mean ED = 52.7; P = 0.004). Our data strongly suggest that altered BDNF levels modulated by BDNF gene variability are associated with the susceptibility to ED, providing physiological evidence that BDNF plays a role in the development of AN and BN, and strongly arguing for its involvement in eating behavior and body weight regulation.

Action monitoring and perfectionism in anorexia nervosa

To study action monitoring in anorexia nervosa, behavioral and EEG measures were obtained in underweight anorexia nervosa patients (n=17) and matched healthy controls (n=19) while performing a speeded choice-reaction task. Our main measures of interest were questionnaire outcomes, reaction times, error rates, and the error-related negativity ERP component. Questionnaire and behavioral results indicated increased perfectionism in patients with anorexia nervosa. In line with their perfectionism and controlled response style patients made significantly less errors than controls. However, when controlling for this difference in error rates, the EEG results demonstrated a reduced error-related negativity in the patient group. These seemingly contradictory outcomes of improved performance and reduced error monitoring are discussed in relation with indications of anterior cingulate cortex hypoactivity in anorexia nervosa patients.

Association of catecholamine-O-methyltransferase and 5-HTTLPR genotype with eating disorder-related behavior and attitudes in females with eating disorders

OBJECTIVE

There is growing evidence, that genetic variants contribute to the pathogenesis of anorexia nervosa and bulimia nervosa. Genetic studies have revealed candidate genes, but no satisfactory associations with the disorders have been found so far. The aim of the present study was to evaluate, whether behavioral and attitudinal traits of the disorders can serve as phenotypes with a possible association with two common functional polymorphisms of the monoaminergic pathways.

METHOD

Forty-five female in-patients of a specialized hospital for eating disorders were included into the study. Eating disorder symptomatology was assessed using the Eating Disorder Inventory-2. The functional catecholamine-O-methyltransferase (COMT) 158 Val-->Met polymorphism and the deletion/insertion polymorphism of the serotonin transporter promoter 5-HTTLPR were determined.

RESULTS

Carriers of at least one Met-allele of the COMT gene had significantly higher total scores of the Eating Disorder Inventory-2, as well as significantly higher scores on the subscales bulimia, ineffectiveness, interoceptive awareness, maturity fears and impulse regulation. Carriers of the deletion of the 5-HTTLPR had significantly higher scores on the subscales drive for thinness and body dissatisfaction.

CONCLUSION

We found associations between the COMT and the 5-HTTLPR polymorphisms and specific clinical, behavioral and attitudinal traits of eating disorders. These polymorphisms may predispose their carriers to exhibit certain symptoms of eating disorders or confer a general risk for more severe forms of these disorders.

Genetics in eating disorders: extending the boundaries of research

OBJECTIVE: To review the recent literature relevant to genetic research in eating disorders and to discuss unique issues which are crucial for the development of a genetic research project in eating disorders in Brazil. METHOD: A computer literature review was conducted in the Medline database between 1984 and may 2005 with the search terms "eating disorders", "anorexia nervosa", "bulimia nervosa", "binge eating disorder", "family", "twin" and "molecular genetic" studies. RESULTS: Current research findings suggest a substantial influence of genetic factors on the liability to anorexia nervosa and bulimia nervosa. Genetic research with admixed populations should take into consideration sample size, density of genotyping and population stratification. Through admixture mapping it is possible to study the genetic structure of admixed human populations to localize genes that underlie ethnic variation in diseases or traits of interest. CONCLUSIONS: The development of a major collaborative genetics initiative of eating disorders in Brazil and South America would represent a realistic possibility of studying the genetics of eating disorders in the context of inter ethnic groups, and also integrate a new perspective on the biological etiology of eating disorders.

Comorbidity of bipolar and eating disorders: distinct or related disorders with shared dysregulations?

BACKGROUND

The co-occurrence of bipolar and eating disorders, though of major clinical and public health importance, remains relatively unexamined.

METHODS

In reviewing the literature on this comorbidity, we compared bulimia, anorexia nervosa, bulimia nervosa, binge eating disorders and bipolar disorders on phenomenology, course, family history, biology, and treatment response.

RESULTS

Epidemiological studies show an association between subthreshold bipolar disorder and eating disorders in adolescents, and between hypomania and eating disorders, especially binge eating behavior, in adults. Of the clinical studies, most show that patients with bipolar disorder have elevated rates of eating disorders, and vice versa. Finally, the phenomenology, course, comorbidity, family history, and pharmacologic treatment response of these disorders show considerable overlap on all of these parameters. In particular, on phenomenologic grounds--eating dysregulation, mood dysregulation, impulsivity and compulsivity, craving for activity and/or exercise--we find many parallels between bipolar and eating disorders. Overall, the similarities between these disorders were more apparent when examined in their spectrum rather than full-blown expressions.

LIMITATIONS

Despite an extensive literature on each of these disorders, studies examining their overlap across all these parameters are relatively sparse and insufficiently systematic.

CONCLUSIONS

Nonetheless, the reviewed literature leaves little doubt that bipolar and eating disorders--particularly bulimia nervosa and bipolar II disorder--are related. Although several antidepressants and mood stabilizers have shown promise for eating disorders, their clinical use when these disorders co-exist with bipolarity is still very much of an art. We trust that this review will stimulate more rigorous research in their shared putative underlying psychobiologic mechanisms which, in turn, could lead to more rational targeted treatments.