BackgroundDelayed motor development in infancy and family history of psychosis are both associated with increased risk of schizophrenia, but their interaction is largely unstudied.AimTo investigate the association of the age of achieving motor milestones and parental psychosis and their interaction in respect to risk of schizophrenia.MethodsWe 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.ResultsParental 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.ConclusionsParental 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.
Background. Our aim was to investigate how age of achieving early motor developmental milestones differ among subjects with and without a history of parental psychosis and whether parental psychosis may alter the effects of the age of achievement on the risk of schizophrenia. Methods. The study sample comprised 10,307 individuals from the prospective Northern Finland Birth Cohort 1966. A total of 139 (1.3%) cohort members suffered from schizophrenia by the age of 46 years. Out of them 19 (13.7%) had a parent with a history of psychosis, while among the non-psychotic cohort members this figure was 524 (5.2%). Results. Out of eight different motor milestones investigated, parental psychosis associated (p<0.05) with later learning of holding head up, grabbing object, and walking without support. In the parental psychosis group, significant risk factors for schizophrenia included later learning of holding head up and touching thumb with index finger. In the non-parental psychosis group risk estimates were lower and statistical significant milestones were different i.e. turning over, sitting without support, standing up, standing and walking without support. Interactions between parental psychosis and touching thumb with index finger and walking without support was found. Conclusions. Although parental psychosis associated with delays in motor milestones in the first year of life, it does not explain the association between late achievement of motor milestones and later risk for schizophrenia
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