title: Genetic subtype differences in neural circuitry of food motivation in Prader-Willi syndrome.
abstract: BACKGROUND
  Differences in behavioral phenotypes between the two most common subtypes of Prader-Willi syndrome (PWS) (chromosome 15q deletions and maternal uniparental disomy 15 (UPD) indicate that distinct neural networks may be affected. Though both subtypes display hyperphagia, the deletion subgroup shows reduced behavioral inhibition around food, whereas those with UPD are generally more able to maintain cognitive control over food intake impulses.
  
  
  OBJECTIVE
  To examine the neural basis of phenotypic differences to better understand relationships between genetic subtypes and behavioral outcomes. We predicted greater food motivation circuitry activity in the deletion subtype and greater activity in higher order cognitive regions in the UPD group, especially after eating.
  
  
  METHODS
  Nine individuals with PWS due to UPD and nine individuals with PWS due to (type 2) deletion, matched for age, gender and body mass index, underwent functional magnetic resonance imaging (fMRI) while viewing food images during two food motivation states: one before (pre-meal) and one after (post-meal) eating a standardized 500 kcal meal.
  
  
  RESULTS
  Both PWS subgroups showed greater activity in response to food pre- and post-meal compared with the healthy-weight group. Compared with UPD, the deletion subtype showed increased food motivation network activation both pre- and post-meal, especially in the medial prefrontal cortex (mPFC) and amygdala. In contrast, the UPD group showed greater activation than the deletion subtype post-meal in the dorsolateral prefrontal cortex (DLPFC) and parahippocampal gyrus (PHG).
  
  
  CONCLUSIONS
  These preliminary findings are the first functional neuroimaging findings to support divergent neural mechanisms associated with behavioral phenotypes in genetic subtypes of PWS. Results are discussed within the framework of genetic mechanisms such as haploinsufficiency and gene dosage effects and their differential influence on deletion and UPD subtypes, respectively.
authors.affiliation: Department of Psychiatry, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02120, USA. lholsen@partners.org
authors.forename: L M
authors.initials: LM
authors.lastname: Holsen
authors.forename: J R
authors.initials: JR
authors.lastname: Zarcone
authors.forename: R
authors.initials: R
authors.lastname: Chambers
authors.forename: M G
authors.initials: MG
authors.lastname: Butler
authors.forename: D C
authors.initials: DC
authors.lastname: Bittel
authors.forename: W M
authors.initials: WM
authors.lastname: Brooks
authors.forename: T I
authors.initials: TI
authors.lastname: Thompson
authors.forename: C R
authors.initials: CR
authors.lastname: Savage
mesh_terms: D001066:Appetite / Q000235:genetics / Q000502:physiology*; D001921:Brain / Q000503:physiopathology*; D002872:Chromosome Deletion; D002884:Chromosomes, Human, Pair 15 / Q000235:genetics; D005260:Female; D006801:Humans; D006963:Hyperphagia / Q000235:genetics / Q000503:physiopathology* / Q000523:psychology; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net; D010641:Phenotype; D010775:Photic Stimulation; D011218:Prader-Willi Syndrome / Q000235:genetics / Q000503:physiopathology* / Q000523:psychology; D011795:Surveys and Questionnaires; D024182:Uniparental Disomy / Q000235:genetics; D055815:Young Adult