title: Interaction between parental psychosis and early motor development and the risk of schizophrenia in a general population birth cohort.
abstract: BACKGROUND
  Delayed motor development in infancy and family history of psychosis are both associated with increased risk of schizophrenia, but their interaction is largely unstudied.
  
  
  OBJECTIVE
  To investigate the association of the age of achieving motor milestones and parental psychosis and their interaction in respect to risk of schizophrenia.
  
  
  METHODS
  We used data from the general population-based prospective Northern Finland Birth Cohort 1966 (n=10,283). Developmental information of the cohort members was gathered during regular visits to Finnish child welfare clinics. Several registers were used to determine the diagnosis of schizophrenia among the cohort members and psychosis among the parents. Altogether 152 (1.5%) individuals had schizophrenia by the age of 46 years, with 23 (15.1%) of them having a parent with psychosis. Cox regression analysis was used in analyses.
  
  
  RESULTS
  Parental psychosis was associated (P<0.05) with later achievement of holding the head up, grabbing an object, and walking without support. In the parental psychosis group, the risk for schizophrenia was increased if holding the head up (hazard ratio [HR]: 2.46; degrees of freedom [df]=1; 95% confidence interval [95% CI]: 1.07-5.66) and touching the thumb with the index finger (HR: 1.84; df=1; 95% CI: 1.11-3.06) was later. In the group without parental psychosis, a delay in the following milestones increased the risk of schizophrenia: standing without support and walking without support. Parental psychosis had an interaction with delayed touching thumb with index finger (HR: 1.87; df=1; 95% CI: 1.08-3.25) when risk of schizophrenia was investigated.
  
  
  CONCLUSIONS
  Parental psychosis was associated with achieving motor milestones later in infancy, particularly the milestones that appear early in a child's life. Parental psychosis and touching the thumb with the index finger had a significant interaction on risk of schizophrenia. Genetic risk for psychosis may interact with delayed development to raise future risk of schizophrenia, or delayed development may be a marker of other risk processes that interact with genetic liability to cause later schizophrenia.
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Center for Life Course Epidemiology and Systems Medicine, University of Oulu, Oulu, Finland. Electronic address: Emmi.Keskinen@oulu.fi.
authors.forename: E
authors.initials: E
authors.lastname: Keskinen
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Center for Life Course Epidemiology and Systems Medicine, University of Oulu, Oulu, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Marttila
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Marttila
authors.affiliation: Department of Psychiatry, University of Cambridge, Cambridge, UK.
authors.forename: P B
authors.initials: PB
authors.lastname: Jones
authors.affiliation: Department of Psychiatry, University of Cambridge, Cambridge, UK.
authors.forename: G K
authors.initials: GK
authors.lastname: Murray
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland.
authors.forename: K
authors.initials: K
authors.lastname: Moilanen
authors.affiliation: Institute of Clinical Medicine, Psychiatry, University of Eastern Finland, Kuopio, Finland; Department of Psychiatry, Kuopio University Hospital (KUH), Kuopio, Finland; Department of Psychiatry, Lapland Hospital District, Rovaniemi, Finland.
authors.forename: H
authors.initials: H
authors.lastname: Koivumaa-Honkanen
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland; Department of Psychiatry, Länsi-Pohja Healthcare District, Finland; Department of Psychiatry, the Middle Ostrobothnia Central Hospital, Kiuru, Finland; Mental Health Services, Joint Municipal Authority of Wellbeing in Raahe District, Finland; Mental Health Services, Basic Health Care District of Kallio, Finland; Visala Hospital, the Northern Ostrobothnia Hospital District, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Mäki
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Department of Psychiatry, Oulu University Hospital, Oulu, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Isohanni
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Center for Life Course Epidemiology and Systems Medicine, University of Oulu, Oulu, Finland.
authors.forename: E
authors.initials: E
authors.lastname: Jääskeläinen
authors.affiliation: Department of Psychiatry, Center for Clinical Neurosciences, University of Oulu, Oulu, Finland; Medical Research Center of Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland; Center for Life Course Epidemiology and Systems Medicine, University of Oulu, Oulu, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Miettunen
mesh_terms: D000328:Adult; D002648:Child; D016241:Child of Impaired Parents / Q000706:statistics & numerical data; D015331:Cohort Studies; D002658:Developmental Disabilities / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology; D005192:Family Health; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D019957:Motor Skills Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology; D010290:Parents / Q000523:psychology; D011446:Prospective Studies; D011599:Psychopathology; D011618:Psychotic Disorders / Q000453:epidemiology*; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology
keywords: Birth cohort; Motor developmental milestone; Parental psychosis; Risk factor; Schizophrenia