Molecular Psychiatry (2011) 16, 595–603 & 2011 Macmillan Publishers Limited All rights reserved 1359-4184/11 www.nature.com/mp FEATURE REVIEW Role of the evolutionarily conserved response in anorexia nervosa DS Dwyer1,2, RY Horton1 and EJ Aamodt3 1Department of Psychiatry, LSU Health Sciences Center, Shreveport, LA, USA; 2Department of Pharmacology, Toxicology and Neuroscience, LSU Health Sciences Center, Shreveport, LA, USA and 3Department of and Molecular Biology, LSU Health Sciences Center, Shreveport, LA, USA

This review will summarize recent findings concerning the biological regulation of starvation as it relates to anorexia nervosa (AN), a serious eating disorder that mainly affects female adolescents and young adults. AN is generally viewed as a psychosomatic disorder mediated by obsessive concerns about weight, perfectionism and an overwhelming desire to be thin. By contrast, the thesis that will be developed here is that, AN is primarily a metabolic disorder caused by defective regulation of the starvation response, which leads to ambivalence towards food, decreased food consumption and characteristic psychopathology. We will trace the starvation response from yeast to man and describe the central role of (and insulin-like growth factor-1 (IGF-1))/Akt/ F-box transcription factor (FOXO) signaling in this response. Akt is a serine/threonine kinase downstream of the insulin and IGF-1 receptors, whereas FOXO refers to the subfamily of Forkhead box O transcription factors, which are regulated by Akt. We will also discuss how initial bouts of caloric restriction may alter the production of neurotransmitters that regulate appetite and food-seeking behavior and thus, set in motion a vicious cycle. Finally, an integrated approach to treatment will be outlined that addresses the biological aspects of AN. Molecular Psychiatry (2011) 16, 595–603; doi:10.1038/mp.2010.95; published online 14 September 2010 Keywords: Akt; anorexia nervosa; FOXO; Insulin/IGF-1

Introduction a disturbed perspective on body shape and weight that may include denial of the seriousness of the Previous reviews on anorexia nervosa (AN) have current condition. Delayed onset of reproductive effectively covered behavioral aspects of eating dis- maturation and amenorrhea are also commonly orders, genetic findings in anorexia and treatment 1–4 observed. There are two main subtypes of AN, approaches. By contrast, this review will focus restricting type and binge-eating/purging type, that selectively on the possible etiology of AN with special are primarily distinguished by episodes of bingeing emphasis on the biological factors that regulate combined with compensatory strategies, including appetite and food/nutrient-seeking behavior across self-induced vomiting or excessive exercise. Bulimia species. On the basis of this analysis, we develop nervosa (BN) is a closely related eating disorder that the thesis that AN may be caused by defects in the involves binge eating and subsequent inappropriate evolutionarily conserved response to food and nu- behavior (for example, vomiting and laxative abuse) trient shortage associated with reduced caloric intake. to avoid weight gain. Implications for treatment will also be discussed. The prevalence of AN in young women is reported to be in the range of 0.1–0.7%; it is rarer in males with 1,5 AN: description and clinical picture a 10:1 ratio of females to males, whereas BN has an estimated prevalence of 1–2% with a 25:1 female to According to DSM-IV criteria, AN is a mental disorder male ratio.1 These disorders are often considered to characterized by a refusal or failure to maintain or predominantly afflict Western societies, although achieve minimally normal weight (85% of that careful investigation of this issue may support a expected on the basis of the age and height), intense cultural basis for BN, but not AN.6 Together, these two fear of gaining weight despite excessive thinness and eating disorders are more common than schizophrenia or bipolar disorder, and AN has the highest mortality Correspondence: Dr DS Dwyer, Department of Psychiatry, LSU rate of all (B10% or higher).7 Health Sciences Center, 1501 Kings Highway, Shreveport, LA Eating disorders typically first emerge in the mid- 71130, USA. teenage years and may be short-lived and self-limiting E-mail: [email protected] 1 Received 22 March 2010; revised 9 August 2010; accepted 11 in 10–20% of patients. On the other hand, AN is August 2010; published online 14 September 2010 chronic and unremitting in about 20–30% of affected The starvation response in anorexia nervosa DS Dwyer et al 596 individuals. The latter group suffers the most weight starvation, stores are depleted as a source of loss, and is at greatest risk for suicide and serious energy, circulating levels of rise and medical complications, including hypothyroidism, counterregulatory mechanisms are initiated, includ- loss of bone density, disturbances, leuko- ing an increase in output from the sympathetic penia and amenorrhea. Hospitalization is common for nervous system10,11 with stimulation of food-seeking this population with an average cost per hospital stay behavior (foraging). Further discussion of the bio- of $10 000–15 000.8 chemistry and of starvation may be found elsewhere.10,11 Biology of the starvation response Evolutionarily conserved aspects of the starvation response will be the focus of this review. The insulin- Individuals with AN restrict caloric intake to the insulin-like growth factor-1 (IGF-1) /Akt/ F-box tran- point of self-starvation. The physiological reaction to scription factor (FOXO) pathway (depicted in Figure 1) starvation is complex involving both central and has a central role in the regulation of this conserved peripheral responses orchestrated by the nervous, response.13 The Forkhead are transcriptional endocrine and digestive systems.9–11 The goal of the regulators that are divided into subfamilies (FOXA– starvation response is to conserve energy, delay FOXQ) with diverse members, including hepatic growth processes, preserve cellular levels of ATP (in nuclear factor (HNF)-3a (FOXA1), FOXC2 and FOXO3.14 part, by increasing the efficiency of energy metabo- They regulate embryogenesis, cell cycling/differentia- lism) and minimize oxidative damage. This response tion, cell energetics and resistance to oxidative is essential for survival during times of food/nutrient stress.15–17 The FOXO subfamily controls the expres- shortage and is, consequently, highly conserved sion of various genes, such as Mn-superoxide through evolution. In man, starvation elicits acute dismutase, cyclin D, tyrosine hydroxylase, trypto- changes in the , especially the hypothalamus phan hydroxylase and IGF-1 binding .16,17 In and brainstem related to nutrient sensing and satiety, general, Forkhead proteins integrate extracellular a fall in blood levels of insulin, fatty acids and signals with internal conditions to determine meta- (to a lesser degree) and suppression of the bolic state and cell fate. They are tightly regulated by production of anorexigenic factors.12 With chronic Akt, which is downstream of insulin/IGF-1 receptors.

Figure 1 Major components of the evolutionarily conserved starvation response. The insulin-IGF-1/Akt/FOXO signaling pathway is depicted here with human/C. elegans counterparts (e.g., the C. elegans version of the insulin-IGF-1 receptor is DAF-2). In some cases (e.g., PDK-1), the same terminology is used across species. Functional outcomes of signaling are shown at the bottom, and the semi-circle arrow indicates that this response can become a vicious cycle. This scheme is not intended to represent the entire control of feeding and appetite nor the full extent of complex interactions among components of the pathway. Additional neuropeptides, hormones (ghrelin and leptin), receptors and signaling molecules (e.g., Rheb and ) are involved in this regulation, but are beyond the scope of the present review. Moreover, certain functional connections (e.g., S6K1 regulation of AMPK and IRS proteins and rictor-Akt/ serum- and glucocorticoid- inducible kinase -1 interactions) have been omitted for the sake of simplicity.

Molecular Psychiatry The starvation response in anorexia nervosa DS Dwyer et al 597 We suggest that defective regulation of the pathway mutants spontaneously wander off food, consume in Figure 1 may ultimately give rise to AN similar to less and develop more slowly than wild-type counter- insulin deficiency (or resistance) causing diabetes. If parts.25 The tax-4 gene encodes a cyclic nucleotide- this idea is correct, then there should be evidence for gated channel, and interacts genetically with daf-16 similar phenotypes (for example, decreased appetite, (FOXO). It is involved in neuronal development, and reduced food intake and delayed reproductive matura- is expressed in sensory and gustatory neurons, tion) in model organisms with mutations in crucial including the ones that synthesize and release insulin genes that regulate foraging and feeding. In the next molecules, such as DAF-28 and INS-1. An association sections, we will briefly summarize key observations of between defective sensory function and anorexic ‘anorexic phenotypes’ from yeast, Caenorhabditis phenotype in C. elegans is consistent with observa- elegans, Drosophila and mice, and discuss the implica- tions of impaired sensory and gustatory function in tions for disease causation and treatment in AN. AN patients.26,27 Although impaired olfactory func- tion in AN is not a universal finding,28 it is interesting Yeast that a reduction in the hedonic perception of food Saccharomyces cerevisiae undergo characteristic following a stroke was associated with a chronic morphological changes when starved of nutrients, decrease in appetite and weight loss.29 especially nitrogen.18 In response to starvation, Simple genetic mutations can also produce the individual cells elongate and colonies form thin opposite phenotype, such as an increase in food- filaments or pseudohyphae that extend away from seeking behavior and feeding. For example, tph-1 the area of nutrient deficiency. This pseudohyphal mutants, which lack serotonin due to loss of the growth is a primitive form of foraging aimed at synthetic enzyme tryptophan hydroxylase, show locating nutrients over a distance.18,19 Zhu et al.19 increased foraging (turns and reversals) in response reported that Forkhead genes have a critical role in to food deprivation.30,31 Clozapine and olanzapine, the regulation of foraging in S. cerevisiae. Knockout of which antagonize serotonin receptors, mimicked two isoforms of FOXO-related genes (FKH1 and the tph-1 phenotype and stimulated foraging in FKH2) promoted cell elongation and pseudohyphal C. elegans.32 By contrast, inhibition of dopamine D2 growth even under fed conditions. By contrast, receptors with raclopride33 or trifluoperazine and overexpression of FKH2 inhibited the normal foraging fluphenazine32 decreased foraging. These findings response of yeast to nitrogen starvation, that is, it suggest that serotonin and dopamine have similar suppressed activity aimed at locating nutrients. It is roles in the regulation of appetite in C. elegans as they interesting that the Forkhead homologs in yeast also do in man.34 control the cell cycle and sexual differentiation.20 The closest homolog of FOXO in yeast, HCM1, regulates Drosophila melanogaster (fruitfly) the expression of both FKH1 and FKH2.21 A critical observation for the thesis developed here is the finding that the overexpression of FOXO equiva- Caenorhabditis elegans (nematode) lent in Drosophila (dFOXO) produced eating distur- The soil nematode, C. elegans, has emerged as a bances similar to those seen in AN patients.35 Thus, valuable model organism because it has a simple, larvae overexpressing dFOXO dispersed from food, well-defined nervous system, yet exhibits a full range ate less and were smaller in size than wild-type of behavior and learning. Ease of genetic approaches animals, yet were otherwise healthy. Similar to and availability of the complete genome sequence anorexic females, they showed a delay in reproduc- are also major advantages of this organism. Studies in tive maturation. Overexpression of PI3 K (Dp110 in C. elegans, have yielded a number of clues about Drosophila), which is upstream of dFOXO and down- the possible origins of AN. Recent findings by our modulates its activity by Akt, also caused animals to group reveal that reduction-of-function mutations in stray from food, ingest less and grow more slowly.36 the C. elegans insulin/IGF-1 receptor gene (daf-2) Thus, significant changes in the expression of single decrease foraging and feeding (pharyngeal pumping) genes involved in the starvation response can cause after removal of animals from a bacterial food source.22 animals to reduce their food intake and suppress Important insights have also been provided by Mori foraging, which mimics the eating behavior of and colleagues who studied temperature preferences patients with AN. (thermotaxis) related to starvation in mutant animals with so-called abnormal hunger orientation (or Aho Mouse models phenotype).23 Wild-type animals move away from Several observations with genetically altered mice their original cultivation temperature when that are relevant for AN. The spontaneously-occurring temperature is paired with starvation, whereas Aho anx/anx mouse strain is anorexic and shows delayed mutants remain at the original temperature despite growth and various behavioral abnormalities, includ- having been paired with starvation. It is interesting ing tremors, uncoordination and hyperactivity.37 The that the aho-2 mutation was mapped to a C. elegans nature of the genetic lesion has not been established; insulin gene, ins-1.24 however, the eating and behavioral characteristics are A second genetic defect related to thermotaxis, consistent with observed hyperinnervation by seroto- tax-4, results in an ‘anorexic phenotype.’ tax-4 nergic neurons.37 On the other hand, knockout mice

Molecular Psychiatry The starvation response in anorexia nervosa DS Dwyer et al 598 lacking the 5-HT2C serotonergic receptor are obese pathway is regulated or amplified by phosphatases (for and hyperphagic.38 Anorexia (hypophagia) is ob- example, phosphatase and tensin homolog deleted on served in dopamine-deficient mice (because of the chromosome 10 (PTEN)), additional adapters (TRIO; selective knockout of tyrosine hydroxylase in dopa- not shown) and by co-activation by G-proteins, Ga and minergic neurons)39 and in mice lacking the M3 Gbg. Ultimately, signaling converges on the FOXO muscarinic acetylcholine receptor.40 It is worth noting (DAF-16) transcription factor, which regulates the that the M3 receptors regulate insulin secretion from expression of genes controlling energy metabolism, b-cells of the pancreas.41 Serotonin is also known to resistance to oxidative stress and longevity.16,17 Akt and affect insulin secretion and prevents nuclear localiza- serum- and glucocorticoid-inducible kinase-1 phos- tion of FOXO in response to starvation.42 A final phorylate FOXO, which causes cytoplasmic retention knockout strain is worth mentioning here. Mice and inhibits transcriptional activation. By contrast, lacking the insulin receptor substrate-2 (IRS-2) pro- AMP-kinase a-2 subunit, AMPK activates FOXO by tein show various metabolic and developmental phosphorylating different sites on the protein without defects that are more severe in females than males.43 affecting its subcellular localization.50 Similar to Female IRS-2À/À mice are hyperphagic, obese and FOXO, AMPK is activated by starvation, and serves infertile. The data suggest that IRS-2 activity is as a fuel gauge in cells.51 It regulates food intake by normally involved in the suppression of appetite signaling in hypothalamic neurons that sense nutrient and feeding. Although studies of knockout mice can levels.52 Expression of a dominant-negative mutant of shed light on the role of individual genes in the AMPK in the hypothalamus significantly reduces regulation of feeding, there are also limitations to this spontaneous food intake and causes weight loss53— approach, including compensatory adaptations to another anorexic phenotype. gene knockout and altered brain/tissue development Additional signaling molecules involved in the because of a lack of the expressed protein. response to starvation are conserved from yeast to man, including cyclic adenosine monophosphate Defective regulation of the starvation response and (and downstream effectors) and target of rapamycin causation in AN (TOR) and its co-factors, Raptor and Rictor. The TOR pathway integrates signaling from nutrients and Aberrant regulation of the starvation response in AN growth factors to regulate mRNA translation, ribo- may result from primary effects, for example, genetic some biogenesis, metabolism and cell/organism mutations that alter protein function and/or expres- size.54 As shown in Figure 1, there is extensive sion or occur secondary to epigenetic changes crosstalk between TOR, Akt and AMPK.55 A substrate induced by environmental conditions (for example, of TOR, S6 kinase (S6K1), has been implicated in life ). Insulin/IGF-1 signaling is a critical compo- span extension produced by caloric restriction and nent of the overall starvation response. In C. elegans, knockout of S6K1 in mice and C. elegans results in foraging after removal from food is significantly reduced body size, delayed reproductive maturation reduced in mutant strains with defects in the DAF-2 and changes in FOXO expression.56 Moreover, in insulin/IGF-1 receptor.22 Consistent with this obser- C. elegans, DAF-15 (Raptor) expression is regulated vation, IGF-1 is low in patients with AN.44 Further- by DAF-16.57 Intriguingly, the genes coding for human more, children with growth failure due to low levels TOR, Rictor and Raptor are located on chromosomes or absence of IGF-1 routinely have poor appetites.45 1p36, 5p13 and 17q25 (Table 1), respectively. These However, the effects of insulin and IGF-1 on loci may harbor potential risk factor genes for AN foraging/feeding in humans appear paradoxical at (see the next section). first glance. Insulin signals satiety and is anorexigenic Overexpression of FOXO (as well as PI3K and (catabolic) in the brain,46 whereas it is anabolic at the IRS-2) may reduce appetite, food-seeking and eating level of peripheral tissues, such as muscle and fat. in anorexic patients as it does in Drosophila and even Insulin and dietary protein (including amino acids) yeast. In addition, FOX genes regulate the expression elicit a slow rise in IGF-1(over more than 3–4 h), of enzymes, tryptophan hydroxylase58 and tyrosine whereas they suppress the production of IGF-1 bind- hydroxylase,59 which synthesize serotonin and dopa- ing protein-1.47,48 The gradual increase in IGF-1 may mine, respectively. This provides an additional then help to initiate food-seeking behavior similar mechanism for regulating appetite and foraging. The to the proposed role of INS-1/DAF-2 in C. elegans. role of FOXO is complicated because Kim et al.60 have Treatment with IGF-1 often induces a voracious reported that short-term overexpression of FOXO1 in appetite, especially in juvenile patients.49 We spec- hypothalamic neurons of mice (8–10 weeks old) ulate that high levels of insulin suppress feeding, increased food intake and body weight. Furthermore, consistent with its role as a metabolic signal of energy DAF-16 accumulates in the nucleus during acute sufficiency, whereas IGF-1 stimulates feeding to food deprivation, but returns to the cytoplasm with support its activity as a major growth factor. prolonged starvation.61 Thus, FOXO may increase or Insulin/IGF-1 signals through insulin/IGF-1 recep- decrease appetite and feeding depending on the tors and downstream receptor substrates (for example, timing and duration (and possibly location) of its IRS-2 and IRS-4), adapter proteins (Grb2) and effectors, aberrant expression. It is interesting that the binge- including PI3 K, PDK-1 and Akt (see Figure 1). This purging subtypes of AN patients exhibit both

Molecular Psychiatry The starvation response in anorexia nervosa DS Dwyer et al 599 Table 1 Genetic mapping of risk loci for AN/BNa The net result of deficits in the starvation response is that patients fail to exhibit normal appetite or to Chromosomal Candidate genes properly regulate their response to fasting and fuel location shortage. This leads to a vicious cycle. Thus, a bias toward denial of food leads to a reduction in calorie 1p32–36 5HTR1D/SER-4 (5-HT1D serotonin receptor) consumption, and weight loss. As weight loss PI3K (p55)/AAP-1 (phosphoinositide-3 proceeds, production of ancillary signals to initiate kinase, p55 adapter subunit) FOXO6/DAF-16 (F-box transcription factor-6) feeding, such as IGF-1 and dopamine (controlled by AMPK2/AAK-2 (AMP-kinase a-2 subunit/ FOXO), is diminished and the starvation response is AMP-activated kinase) further activated. However, because this response is Gb1/GPB-1 (G protein b-subunit-1) defective in AN, counterregulatory (orexigenic) me- TOR/LET-363 (Target of Rapamycin/lethal-363) chanisms are ineffectual, and a persistent catabolic 1q31.3 — state develops, much like anorexia associated with 2p11.2 — cancer or infectious diseases. The fact that some 5p13–15 AMPK/AAK-1 (AMP-kinase a-1 subunit/ anorexic patients literally starve themselves to death AMP-activated kinase) attests to the failure of evolutionarily conserved TRIO/UNC-73 (Trio adaptor protein/ survival strategies in AN. uncoordinated-73) Rictor/RICT-1 6q21–23 FOXO3/DAF-16 (F-box transcription factor-3) Genetic risk factors in AN SGK-1 (serum- and glucocorticoid-inducible kinase-1) AN shows strong familial association and is highly 7p15.3 NPY/FLP-21 (neuropeptide Y/FMRF-like heritable.7,64 Recent reviews have summarized genetic peptide-21) contributions to the development of eating disorders 9p21.3 — (for example, see Bulik et al.3). These efforts include 11p13–14 BDNF (brain-derived neurotrophic factor) mapping genetic loci associated with increased risk 11q23 DRD2/DOP-2 (D2 dopamine receptor) for developing AN and BN.3,65–68 If our hypothesis 13q11–14 5HTR2A/SER-1 (5-HT2A serotonin receptor) about causal factors in AN is correct, then some FOXO1A/DAF-16 (F-box transcription factor-1A) components of the starvation response should map to 14q32 AKT1/AKT-1 (Akt/protein kinase B) these genetic risk loci. Genetic linkage analysis and 15q25–26 IGF-1R/DAF-2 (insulin-like growth factor-1 association studies have identified risk markers at the receptor) chromosomal locations listed in Table 1. Identifica- 16p13.3 PDK1/PDK-1 (phosphoinositide-dependent tion of the serotonin receptors, 5HTR1D and 5HTR2A, kinase-1) the dopamine D2 receptor, catechol-O-methyltrans- 17q25 Grb2/SEM-5 (growth factor receptor-bound ferase and brain-derived neurotrophic factor as protein 2/sex muscle abnormal-5) candidate susceptibility genes has been reported Raptor/DAF-15 previously,3,68 whereas the others are derived from 22q11 COMT/Y40B10A.6 (catechol-O- our own analysis. methyltransferase) Xq22.3 IRS4/IST-1 (insulin receptor substrate-4) As seen in Table 1, numerous components of the starvation response are located in the vicinity of the a putative AN/BN genetic risk loci discovered in The list of chromosomal regions implicated in genetic linkage 3,65–68 analysis of AN/BN was compiled from several recent genome-wide linkage analysis, which would be papers.3,65–69 Candidate genes (human/C. elegans counterparts) consistent with our hypothesis that FOXO1, FOXO3, were identified by examining these chromosomal regions for AKT1, serum- and glucocorticoid-inducible kinase-1, the presence of any components of the starvation response AMPK and IRS4 may constitute risk factors for depicted in Figure 1. For several loci, our analysis and that of AN. Despite the fact that some of the linkages are based others failed to identify plausible candidate genes (À), whereas on behavioral phenotypes (for example, anxiety or in other cases multiple genes were located near the marker site. obsessionality), it is quite remarkable that so many genes involved in the control of energy metabolism extremes of eating behavior. Taken together, these map to these risk loci. Additional components related studies confirm a vital role for FOXO in controlling to this pathway—the IGF-1 receptor and neuropep- appetite and feeding across evolution. tide Y—have been implicated by a genome-wide The role of other genes depicted in Figire 1 may analysis of genes involved in the maintenance of fat- likewise be complex. For example, TAX-4 (cyclic free body mass.69 We consider it highly unlikely that nucleotide-gated channel) affects the development of these observations are the result of chance. However, sensory neurons.62 Consequently, defects in this gene to formally address this issue, we arbitrarily selected might impair sensation of food-related cues that 11 genes from similar overall classes as those listed in normally stimulate eating. Alternatively, cyclic the table to determine the frequency of ‘hits’ at risk nucleotide-gated channels gated by cyclic guanosine loci. The panel included the a2C adrenergic receptor, monophosphate may be required for ongoing regula- b2-adrenergic receptor, cholecystokinin, interleukin-2 tion of feeding mediated by nitric oxide in hypo- receptor, protein kinase A-a, platelet-derived growth thalamic neurons.63 factor receptor-b (PDGFRB), glutathione reductase,

Molecular Psychiatry The starvation response in anorexia nervosa DS Dwyer et al 600 glutamate dehydrogenase, flavin adenine dinucleo- changes in neurotransmitter production mediated tide synthetase (FLAD1) and glucose-dependent by FOXO. Bergh and So¨dersten71 proposed that insulinotropic polypeptide receptor. None of these self starvation has rewarding properties in anorexic genes were close to any of the risk loci listed in Table patients. Thus, caloric restriction and weight loss 1. Furthermore, genes coding for various cytokines predispose to additional episodes of , espe- that regulate feeding, for example, leptin (7q32.1), cially in susceptible individuals with defective ghrelin (3p25.3) and adiponectin (3q27.3) do not map regulation of their starvation response, or with a to these regions. Leptin and other hormone regulators perseverative bias in behavior, reflected in obsessive of appetite/feeding may indeed have a role in AN, thoughts and compulsivity. however, as yet, a genetic contribution has not been Although personality traits and psychological fac- established. tors modify the course of AN, they may not be Genetic models for the etiology of AN should be fundamental causative agents, and may, in fact, be a able to explain gender differences in the relative response to starvation. This possibility is raised by incidence of eating disorders (that is, females >> the pioneering work of Keys and colleagues9 on the males). Signaling by IRS proteins potentially repre- effects of semi-starvation in normal college-age males. sents one such difference between the sexes. Knock- Male volunteers were subjected to severe caloric out of the IRS-2 gene had a much greater impact on restriction over a period of 24 weeks, followed by reproductive maturation and food intake in female gradual restoration of calories over a 12–week than male mice.43 IRS-2 normally suppresses food rehabilitation phase. Over the course of these studies, intake related to insulin signaling in the brain, subjects lost an average of 37 pounds or nearly 25% whereas the closely related protein, IRS-4, signals of their starting weight. They became progressively downstream of leptin.70 The gene for IRS-4 is located anxious, irritable, depressed, preoccupied with food on the X chromosome at Xq22.3, which was identified and exhibited obsessive ideations. These psychologi- as a possible risk locus for AN by Devlin et al.66 cal changes persisted in many subjects even after Overexpression of IRS-4 in females, perhaps as the refeeding. During the rehabilitation phase, many result of escape from X chromosome inactivation, expressed concerns about gaining too much weight might suppress eating similar to IRS-2. Of course, and ‘becoming flabby.’ Most subjects did not return to many other gender differences might contribute to the their pre-study weights even after 12 weeks of free higher rate of AN in women than men. access to food; environmental factors (fasting) appear The genetic data cited here should be considered to have altered metabolic set points, such as baseline preliminary in nature. Although the studies are solid body weight. From case reports and diary entries and adequately controlled, many findings have not yet during natural periods of food shortage in wars and been replicated. Moreover, population size is often famine, Keys et al.9 found numerous examples limited, some of the linkages are weak, and associa- where starvation was accompanied by mental illness, tions with individual genes remain controversial. Yet, including depression, anxiety, psychosis and even the overall picture emerging from the genetic analysis suicide. Thus, in normal individuals, starvation is consistent with what would be expected for a elicits the same type of psychopathology seen in disorder with a polygenic origin and modest contribu- patients with AN, as observed previously by Bergh, tions by multiple genes. At this stage, the genetic So¨dersten and colleagues.4,71 In this context, it is findings offer attractive candidates for further evalua- noteworthy that prolonged voluntary starvation (for tion rather than definitive causal factors for AN. example, a hunger strike) is associated with a reduction in sense of harm and significant loss of appetite, even after the self-imposed fast has Role of culture and the environment in eating ended.72,73 disorders

Although this review is focused on biological factors Implications for treatment in AN, it is clear that a culture of thinness and dieting contribute to the prevalence of eating disorders. Psychotherapy and behavior-based therapies However, culture and environment may affect the Eating disorders are notoriously difficult to treat, and propensity for AN in unsuspected ways. AN occurs noncompliance is a major issue, which arises in part throughout the world, not just in western cultures because of denial of the seriousness of the condition. that equate beauty with thinness.6 It has also existed Therapy for AN consists mainly of behavioral cogni- in different historical periods when people had tive approaches and psychotherapy.74,75 divergent notions of the ideal body shape for women.6 The first concern for clinicians treating eating- Nevertheless, cultural attitudes and norms may disordered patients is to identify and manage any trigger an initial bout of dieting in adolescents physical complications of the eating disorder. Pa- concerned about their appearance, and dieting itself tients are often fearful of treatment that will result in is a risk factor for AN.4 A first episode of excessive weight gain. Therefore, even at the initial stages caloric restriction to induce weight loss appears to of treatment, psychotherapeutic techniques are begun cause homeostatic adaptation in the starvation re- in an effort to engage reluctant patients as participants sponse that may be accompanied by long-term in their own care. Cognitive-behavioral therapy

Molecular Psychiatry The starvation response in anorexia nervosa DS Dwyer et al 601 techniques have been helpful in managing eating- IGF-1 may not be desirable in view of the side disordered patients. Cognitive restructuring is used to effect profile, which includes lymphoid hyperplasia, help patients correct cognitive distortions, including accumulation of fat tissue and potential tumor a distorted body image. promotion.88 In addition, family therapy addresses the family Xanomeline, or similar drugs, may represent a interactions and relationships, and helps family future approach to the treatment of AN. Xanomeline members gain a better understanding of the disorder. is a selective muscarinic agonist that showed anti- Common goals in family therapy include improving psychotic properties in a recent clinical trial,89 and communication, minimizing conflicts and allowing also improved cognitive function in Alzheimer’s the patient to feel supported, while retaining some patients.90 Muscarinic cholinergic function is reduced independence. Randomized controlled trials of fa- in anorexic patients.91 Furthermore, muscarinic re- mily-based therapies have shown significant positive ceptors modulate insulin release by the pancreas,41 effects on clinical outcomes in adolescent pa- and regulate the starvation response of C. elegans, tients.76,77 A recent meta-analysis of controlled stu- including dauer formation.92,93 Muscarinic agonists dies of family therapy supported the main conclusion also mimic certain effects of insulin and IGF-1 in that this approach is effective in adolescents over the neuroblastoma cells.94 short term, however, long-term advantages were less The medications discussed here should be consid- clear, and some trials found no significant benefit.78 ered experimental drugs that require further testing to More research is needed to determine whether family demonstrate their utility and safety in treating AN. therapy, combined with biological approaches, repre- They also represent a shift in therapeutic strategy sents a superior strategy for treatment. toward the management of AN as a metabolic Efforts to treat AN solely with behavioral ap- disorder. According to this approach, the goal of proaches may have had limited success because they therapy would be to interrupt the starvation response, target the sequelae of the disorder rather than the correct or compensate for defective counterregulation, etiology, and rely on ‘will power’ when the real stimulate appetite and normalize eating habits. In our culprit may be a metabolic defect akin to the situation view, a combination of pharmacotherapy and beha- in diabetes mellitus. vior-based strategies will be required to accomplish this challenging task. Pharmacotherapy There is no recognized drug treatment for AN. Anti- depressants have been used, but the results have Conflict of interest largely been disappointing.1,79 Anxiolytics are pre- scribed to reduce anxiety in AN patients, whereas Dr Dwyer’s and Dr Aamodt’s research has been anti-psychotic drugs are indicated when delusions funded by the NIH. Dr Dwyer has previously or psychotic features are present. In general, drugs consulted for Eli Lilly and Co. and received compen- are used to treat co-morbid conditions associated sation. Drs Aamodt and Horton declare no conflict of with AN. interest. Although there is an urgent need to develop new drugs for the effective treatment of AN, several current medications warrant further evaluation as Acknowledgments interim therapeutic agents. Olanzapine is an atypical This work was supported by a grant from the Edward anti-psychotic drug that causes significant weight 80 P Stiles Trust Fund (LSUHSC) and Biomedical gain, especially in adolescents. In C. elegans,it Research Foundation of Northwest Louisiana. blocks the starvation response (nuclear localization of FOXO/DAF-16),81 stimulates foraging,32 and induces 82 significant lipid accumulation. This profile of References biological activity appears to be well suited for addressing the main deficits in AN. Small open-label 1 Fairburn CG, Harrison PJ. Eating disorders. 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