Evidence for phenotypic plasticity in response to photic cues and the connection with genes of risk in schizophrenia

Abstract

Numerous environmental factors have been identified as influential in the development of schizophrenia. Some are byproducts of modern life, yet others were present in our evolutionary past and persist to a lesser degree in the current era. The present study brings together published epidemiological data for schizophrenia and data on variables related to photic input for places of residence across geographical regions, using rainfall as an inverse, proxy measure for light levels. Data were gathered from the literature for two countries, the former Yugoslavia and Ireland, during a time in the early 20th century when mobility was relatively limited. The data for Yugoslavia showed a strong correlation between hospital census rates for schizophrenia (by place of birth) and annual rain (r = 0.96, p = 0.008). In Ireland, the hospital census rates and first admissions for schizophrenia (by place of permanent residence) showed a trend for correlation with annual rain, reaching significance for 1st admissions when the rainfall data was weighted by the underlying population distribution (r = 0.71, p = 0.047). In addition, across the years 1921–1945, birth-year variations in a spring quarter season-of-birth effect for schizophrenia in Ireland showed a trend for correlation with January-March rainfall (r = 0.80, p ≤ 0.10). The data are discussed in terms of the effect of photoperiod on the gestation and behavior of offspring in animals, and the premise is put forth that vestigial phenotypic plasticity for such photic cues still exists in humans. Moreover, genetic polymorphisms of risk identified for psychotic disorders include genes modulated by photoperiod and sunlight intensity. Such a relationship between phenotypic plasticity in response to a particular environmental regime and subsequent natural selection for fixed changes in the environmentally responsive genes, has been well studied in animals and should not be discounted when considering human disease.

Vitamin D in schizophrenia: a clinical review

“…Several environmental risk factors for schizophrenia, such as season of birth, latitude and migration, have been linked to vitD deficiency 16 17 20…”

“…There also seems to be a relationship between the risk of schizophrenia and latitude, with an increased incidence rate of schizophrenia seen at a higher latitude 17. Miller hypothesises that the observed relationship may be related to UVB availability: individuals at higher latitudes tend to receive substantially less vitD than individuals at lower latitudes; 21 furthermore, at latitudes above 35°, the UVB rays required to make vitD are not available during the winter months 1.…”

“…The shorter day lengths and less intense sunlight that individuals receive at higher latitudes decrease an individual's vitD intake. The reduced vitD intake is more pronounced in darker skinned individuals as the lighter skin that individuals at higher latitudes tend to display is a result of their decreased melanin that allows the skin to absorb UVB light more effectively and synthesise vitD 17. Thus, an individual migrating from a warmer to a colder climate receives less vitD 1.…”

Season of birth and population schizotypy: Results from a large sample of the adult general population

“…Several explanations for a seasonal effect on the liability to schizophrenia have been proposed and proceed mainly on the assumption that SOB acts as a proxy indicator for increased perinatal vulnerability during winter and early spring time. These harmful environmental factors at the end of pregnancy and at time of birth range from ambient temperature, reduced maternal sunlight exposure and deficient vitamin D generation to perinatal viral exposures (McGrath and Welham, 1999;Miller, 2013;Schwartz, 2011;Tochigi et al, 2004;Torrey et al, 1997).…”

Schizophrenia: A Consequence of Gene-Environment Interactions?

“…Finally, Miller assessed the impact of photic cues on the development of schizophrenia. Her argument for a role for photic cues in the disorder is made more compelling given that single nucleotide polymorphisms have been found in genes relevant to schizophrenia, which are modulated by photoperiod and sunlight intensity (Miller, 2013).…”