Genetics in eating disorders: extending the boundaries of research

Temporal changes in the prevalence of disordered eating behaviors among adolescents living in the metropolitan area of Rio de Janeiro, Brazil

To investigate temporal changes in the prevalence of disordered eating behaviors among adolescents, and their association with socio demographic factors and overweight. Using probability sampling, two population-based cross-sectional surveys were conducted: one in 2005 (n=511) and the other in 2010 (n=314). The frequency of disordered eating behaviors (binge eating, strict dieting or fasting and compensatory behaviors) was investigated using a self-administered questionnaire. The presence of binge eating increased by 18.4% in the 5 years between the two surveys. In 2005, girls were 1.95 times more likely to engage in strict dieting or fasting than boys, and this difference increased to 7.02 times in 2010. Overweight adolescents were 2.29 times more likely to undertake strict dieting than non-overweight adolescents in 2005 and 3.65 times more likely to do so in 2010. No significant associations were found for compensatory behaviors. A pronounced increase in the prevalence of binge eating was observed, and girls and overweight adolescents were more likely to engage in strict dieting or fasting.

Evidence for three genetic loci involved in both anorexia nervosa risk and variation of body mass index

The maintenance of normal body weight is disrupted in patients with anorexia nervosa (AN) for prolonged periods of time. Prior to the onset of AN, premorbid body mass index (BMI) spans the entire range from underweight to obese. After recovery, patients have reduced rates of overweight and obesity. As such, loci involved in body weight regulation may also be relevant for AN and vice versa. Our primary analysis comprised a cross-trait analysis of the 1000 single-nucleotide polymorphisms (SNPs) with the lowest P-values in a genome-wide association meta-analysis (GWAMA) of AN (GCAN) for evidence of association in the largest published GWAMA for BMI (GIANT). Subsequently we performed sex-stratified analyses for these 1000 SNPs. Functional ex vivo studies on four genes ensued. Lastly, a look-up of GWAMA-derived BMI-related loci was performed in the AN GWAMA. We detected significant associations (P-values <5 × 10-5, Bonferroni-corrected P<0.05) for nine SNP alleles at three independent loci. Interestingly, all AN susceptibility alleles were consistently associated with increased BMI. None of the genes (chr. 10: CTBP2, chr. 19: CCNE1, chr. 2: CARF and NBEAL1; the latter is a region with high linkage disequilibrium) nearest to these SNPs has previously been associated with AN or obesity. Sex-stratified analyses revealed that the strongest BMI signal originated predominantly from females (chr. 10 rs1561589; Poverall: 2.47 × 10-06/Pfemales: 3.45 × 10-07/Pmales: 0.043). Functional ex vivo studies in mice revealed reduced hypothalamic expression of Ctbp2 and Nbeal1 after fasting. Hypothalamic expression of Ctbp2 was increased in diet-induced obese (DIO) mice as compared with age-matched lean controls. We observed no evidence for associations for the look-up of BMI-related loci in the AN GWAMA. A cross-trait analysis of AN and BMI loci revealed variants at three chromosomal loci with potential joint impact. The chromosome 10 locus is particularly promising given that the association with obesity was primarily driven by females. In addition, the detected altered hypothalamic expression patterns of Ctbp2 and Nbeal1 as a result of fasting and DIO implicate these genes in weight regulation.

Parental disorders, childhood abuse, and binge eating in a large community sample

OBJECTIVE

Genetic and nonshared environmental factors are implicated in the etiology of binge eating behaviors (BEB), with genetic risk expressed as parental psychopathology. Traumatic experiences including child abuse predict onset of BEB. It is not clear if each separately contribute to BEB, or whether parental pathology leads to abuse which in turn influences BEB.

METHOD

Data were obtained from the National Comorbidity Survey-Replication (N = 2960). Through structural equation modeling, we estimated unique and combined effects of mother's and father's internalizing (INT) and externalizing (EXT) disorders, and child abuse on BEB.

RESULTS

Parental INT and EXT psychopathology contributed to child abuse and BEB. Abuse predicted BEB and partially mediated associations between parental psychopathology and BEB.

DISCUSSION

Results emphasize the value of models that incorporate nature and nurture to understand risk for psychopathology in offspring, with childhood abuse being one mediator of how parental psychopathology may reflect genetic risk and influence environmental risk.

Fat mass and obesity-associated gene (FTO) in eating disorders: evidence for association of the rs9939609 obesity risk allele with bulimia nervosa and anorexia nervosa

OBJECTIVE

The common single nucleotide polymorphism (SNP) rs9939609 in the fat mass and obesity-associated gene (FTO) is associated with obesity. As genetic variants associated with weight regulation might also be implicated in the etiology of eating disorders, we evaluated whether SNP rs9939609 is associated with bulimia nervosa (BN) and anorexia nervosa (AN).

METHODS

Association of rs9939609 with BN and AN was assessed in 689 patients with AN, 477 patients with BN, 984 healthy non-population-based controls, and 3,951 population-based controls (KORA-S4). Based on the familial and premorbid occurrence of obesity in patients with BN, we hypothesized an association of the obesity risk A-allele with BN.

RESULTS

In accordance with our hypothesis, we observed evidence for association of the rs9939609 A-allele with BN when compared to the non-population-based controls (unadjusted odds ratio (OR) = 1.142, one-sided 95% confidence interval (CI) 1.001-∞; one-sided p = 0.049) and a trend in the population-based controls (OR = 1.124, one-sided 95% CI 0.932-∞; one-sided p = 0.056). Interestingly, compared to both control groups, we further detected a nominal association of the rs9939609 A-allele to AN (OR = 1.181, 95% CI 1.027-1.359, two-sided p = 0.020 or OR = 1.673, 95% CI 1.101-2.541, two-sided p = 0.015,).

CONCLUSION

Our data suggest that the obesity-predisposing FTO allele might be relevant in both AN and BN.

Genetic variation of the ghrelin activator gene ghrelin O-acyltransferase (GOAT) is associated with anorexia nervosa

The gastrointestinal peptide hormone ghrelin promotes food intake and increases body weight and adiposity through activation of the growth hormone secretagogue receptor (GHSR1a). To promote its biological action ghrelin is acylated at its serine 3 residue by the recently discovered ghrelin O-acyltransferase (GOAT, a.k.a. membrane-bound O-acyltransferase 4, MBOAT4). Plasma levels of total and acyl-ghrelin are negatively correlated with body-mass-index (BMI); as lower the BMI as higher plasma levels of total and acylated ghrelin and vice versa. Accordingly, plasma levels of total and acyl-ghrelin are elevated in patients with anorexia nervosa (AN) and decline upon weight regain. The importance of the endogenous Goat/ghrelin system in the neuroendocrine adaptation to fasting was recently highlighted by the observation that acyl-ghrelin mediated elevation of growth hormone (GH) release prevents starvation induced hypoglycemia in Goat(-/-) mice. The aim of this study was to test if genetic variation of GOAT is implicated in the etiology of AN. We therefore assessed association of 6 tagging single nucleotide polymorphisms (tagSNPs), which were predicted to cover 96% the common genetic variability of GOAT plus 50 kb of the 5' and 3' flanking region, in 543 German patients with AN and 612 German normal and underweight healthy controls. Based on a recessive mode of inheritance we observed some evidence for association of the G/G genotype at SNP rs10096097 with AN (nominal two-sided p = 0.031). Based on our results we conclude that genetic variation in GOAT might be implicated in the etiology of AN.

Patterns of co-morbidity of eating disorders and substance use in Swedish females

BACKGROUND

Little is known about the association of eating disorder subtypes across multiple categories of substance use in population-based samples. We examined the association between eating disorders and substance use in a large population-based sample.

METHOD

Female participants (n=13 297) were from the Swedish Twin Registry [Lichtenstein et al., Twin Research and Human Genetics (2006) 9, 875-882]. Substance use was examined in four defined groups - (1) anorexia nervosa (AN); (2) bulimia nervosa (BN); (3) AN and BN (ANBN); and (4) binge eating disorder (BED) as well as a referent group without eating disorder (no ED). Secondary analyses examined differences between restricting AN (RAN) and binge and/or purge AN (ANBP).

RESULTS

In general, eating disorders were associated with greater substance use relative to the referent. The AN group had significantly increased odds for all illicit drugs. Significant differences emerged across the RAN and ANBP groups for alcohol abuse/dependence, diet pills, stimulants, and polysubstance use with greater use in the ANBP group. Across eating disorder groups, (1) the BN and ANBN groups were more likely to report alcohol abuse/dependence relative to the AN group, (2) the ANBN group was more likely to report diet pill use relative to the AN, BN and BED groups, and (3) the BN group was more likely to report diet pill use relative to the no ED, AN and BED groups.

CONCLUSIONS

Eating disorders are associated with a range of substance use behaviors. Improved understanding of how they mutually influence risk could enhance understanding of etiology and prevention.

Identification of novel candidate loci for anorexia nervosa at 1q41 and 11q22 in Japanese by a genome-wide association analysis with microsatellite markers

The Japanese Genetic Research Group for Eating Disorders (JGRED) is a multisite collaborative study group that was organized for the systematic recruitment of patients with an eating disorder for the purpose of genetic study in Japan. We conducted a genome-wide case-control association study using 23 465 highly polymorphic microsatellite (MS) markers to identify genomic loci related to anorexia nervosa (AN). Pooled DNA typing in two screening stages, followed by individual typing of 320 AN cases and 341 controls, allowed us to identify 10 MS markers to be associated with AN. To narrow down genomic regions responsible for the association of these MS markers, we further conducted a single-nucleotide polymorphism (SNP) association analysis for 7 of the 10 loci in 331 AN cases and 872 controls, which include the 320 AN cases and the 341 controls genotyped in the MS screening, respectively. Two loci, namely 1q41 and 11q22, remained significantly associated with AN in the SNP-based fine mapping, indicating the success in narrowing down susceptibility regions for AN. Neither of these loci showed a positive evidence of association with bulimia nervosa. The most significant association was observed at SNP rs2048332 (allelic P-value=0.00023) located at 3'-downstream of the SPATA17 gene on the 1q41 locus. The association analysis for MS-SNP haplotypes detected a statistically significant association (permutation P-value=0.00003) of the A-4-G-T haplotype that comprised four SNP/MS markers (rs6590474-D11S0268i-rs737582-rs7947224) on the 11q22 locus with AN. This linkage disequilibrium block spanning a 20.2-kb interval contains exon 9 of the CNTN5 gene encoding contactin 5.