title: Insulin-Like Growth Factor 1 (IGF-1) in Parkinson's Disease: Potential as Trait-, Progression- and Prediction Marker and Confounding Factors.
abstract: BACKGROUND
  Biomarkers indicating trait, progression and prediction of pathology and symptoms in Parkinson's disease (PD) often lack specificity or reliability. Investigating biomarker variance between individuals and over time and the effect of confounding factors is essential for the evaluation of biomarkers in PD, such as insulin-like growth factor 1 (IGF-1).
  
  
  METHODS
  IGF-1 serum levels were investigated in up to 8 biannual visits in 37 PD patients and 22 healthy controls (HC) in the longitudinal MODEP study. IGF-1 baseline levels and annual changes in IGF-1 were compared between PD patients and HC while accounting for baseline disease duration (19 early stage: ≤3.5 years; 18 moderate stage: >4 years), age, sex, body mass index (BMI) and common medical factors putatively modulating IGF-1. In addition, associations of baseline IGF-1 with annual changes of motor, cognitive and depressive symptoms and medication dose were investigated.
  
  
  RESULTS
  PD patients in moderate (130±26 ng/mL; p = .004), but not early stages (115±19, p>.1), showed significantly increased baseline IGF-1 levels compared with HC (106±24 ng/mL; p = .017). Age had a significant negative correlation with IGF-1 levels in HC (r = -.47, p = .028) and no correlation in PD patients (r = -.06, p>.1). BMI was negatively correlated in the overall group (r = -.28, p = .034). The annual changes in IGF-1 did not differ significantly between groups and were not correlated with disease duration. Baseline IGF-1 levels were not associated with annual changes of clinical parameters.
  
  
  CONCLUSIONS
  Elevated IGF-1 in serum might differentiate between patients in moderate PD stages and HC. However, the value of serum IGF-1 as a trait-, progression- and prediction marker in PD is limited as IGF-1 showed large inter- and intraindividual variability and may be modulated by several confounders.
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Felix P
authors.initials: FP
authors.lastname: Bernhard
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Heinzel
authors.affiliation: Department of Pediatric Endocrinology, University Children`s Hospital Tuebingen, Tuebingen, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Binder
authors.affiliation: Department of Pediatric Endocrinology, University Children`s Hospital Tuebingen, Tuebingen, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Weber
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Apel
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.|German Center for Neurodegenerative Diseases (DZNE), Tuebingen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Roeben
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Deuschle
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Maechtel
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Heger
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Nussbaum
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.|German Center for Neurodegenerative Diseases (DZNE), Tuebingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gasser
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.|German Center for Neurodegenerative Diseases (DZNE), Tuebingen, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Maetzler
authors.affiliation: Department of Neurodegeneration, Hertie Institute for Clinical Brain Research (HIH), University of Tuebingen, Tuebingen, Germany.|German Center for Neurodegenerative Diseases (DZNE), Tuebingen, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Berg
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000378:metabolism*; D015992:Body Mass Index; D018450:Disease Progression; D005260:Female; D018703:Founder Effect; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000097:blood / Q000175:diagnosis*; D015203:Reproducibility of Results; D012307:Risk Factors
chemical_list: D015415:Biomarkers; C583557:IGF1 protein, human; D007334:Insulin-Like Growth Factor I