Alterations of White Matter Integrity Related to the Season of Birth in Schizophrenia: A DTI Study

<div><p>In schizophrenia there is a consistent epidemiological finding of a birth excess in winter and spring. Season of birth is thought to act as a proxy indicator for harmful environmental factors during foetal maturation. There is evidence that prenatal exposure to harmful environmental factors may trigger pathologic processes in the neurodevelopment, which subsequently increase the risk of schizophrenia. Since brain white matter alterations have repeatedly been found in schizophrenia, the objective of this study was to investigate whether white matter integrity was related to the season of birth in patients with schizophrenia. Thirty-four patients with schizophrenia and 33 healthy controls underwent diffusion tensor imaging. Differences in the fractional anisotropy maps of schizophrenia patients and healthy controls born in different seasons were analysed with tract-based spatial statistics. A significant main effect of season of birth and an interaction of group and season of birth showed that patients born in summer had significantly lower fractional anisotropy in widespread white matter regions than those born in the remainder of the year. Additionally, later age of schizophrenia onset was found in patients born in winter months. The current findings indicate a relationship of season of birth and white matter alterations in schizophrenia and consequently support the neurodevelopmental hypothesis of early pathological mechanisms in schizophrenia.</p></div

Interaction of group and season of birth.

<p>(A) Summer-born patients with schizophrenia showed reduced FA values compared to winter-born patients with schizophrenia within the areas indicated in red. (B) The plot shows the mean FA values within the significant TBSS clusters highlighted in red in summer and winter-born patients. For the purpose of comparison, mean FA values extracted from the same areas indicated in red were additionally displayed for summer and winter-born controls. The TBSS images show results at <i>p</i><0.03 corrected for multiple comparisons.</p

Demographic data of patients with schizophrenia and controls, separated for seasons of birth.

<p>Except for age range, gender, migration, social adversity and cannabis use, values are represented as mean ± standard deviation. M, male; F, female; PANSS, Positive and Negative Syndrome Scale; PANSS-P, subscale for positive symptoms; PANSS-N, subscale for negative symptoms; PANSS-T, total score of PANSS, CPZ, chlorpromazine equivalents.</p

Interaction of group and season of birth shows reduced FA values in summer-born patients compared to winter-born patients with schizophrenia.

<p>MNI, Montreal Neurological Institute; FA, fractional anisotropy; SD, standard deviation.</p

Significant main effect of season of birth.

<p>(A) Summer-born subjects have lower FA values than winter-born subjects in the regions indicated in red. (B) The plot shows the mean FA values in summer and winter-born subjects within the significant TBSS clusters of the main effect of season highlighted in red. The TBSS images show results at <i>p</i><0.05 corrected for multiple comparisons.</p

Distribution of the months of birth across the year for patients and controls.

<p>The x-axes of the bar plot displays the months from January to December, each abbreviated by the first letter. The y-axis reports the frequency of births.</p