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.

Keywords: epidemiology; melanotropin; natural light; photoperiod; prenatal; pyschoses; schizophrenia; vitamin D.

Figure 1

Rates of schizophrenia hospitalization in the year 1931 (A) vs. the average annual rainfall, 1925–1940 (B) for the former Yugoslavia. The hospitalization rates are plotted by place of the patient's birth (derived from Crocetti et al., 1964).

Figure 2

Maps showing the distribution of non-Slavic ethnic groups within the former Yugoslavia (reprinted from Banac, with permission from Cornell University Press). The left panel depicts regions where Germans (Ger.) and Albanians (Alb.) constitute from 5 to 100% of the population. The right panel depicts regions where Hungarians (Hun.) and Turkish communities (Turk.) constitute 5–100% of the population. In the left panel, the regions with significant Germanic communities lie exclusively within the top half of the map, and the regions with significant Albanian communities within the bottom half of the map. In the right panel, the regions with significant Hungarian communities lie within the top half of the map and the regions with significant Turkish communities within the bottom half of the map.

Figure 3

Rates of schizophrenia 1st admissions (left panel) vs. annual rainfall (right panel) in Ireland. The 1st admissions digital plot represent means of the yearly values in the outlined health catchment area (S, MW, W, NW, MID, NE, E, and SE), calculated for 1982–1991 from data published by the Health Research Board for Ireland (Activities of Irish Psychiatric Hospitals and Units Dublin, Ireland). The annual rainfall digital plot (derived from the Irish Meteorological Service, Galway and Logue, 1984) represents means of the yearly totals for 1941–1970, which would have included the birth years for many of the 1st admission patients.

Figure 4

The relationship between the percent excess (of average for weather stations in Ireland) of Jan–Mar rain and the percent excess of 2nd quarter schizophrenia births (as compared to the year-round quarterly average for 5 year period) for time periods spanning the years 1921–1945 (season-of-birth data derived from O'Hare et al., 1980). Note that Jan-Mar rain was not available from the series “British Rainfall” for the war year 1941, and thus the data point for the rainfall does not include 1941, though the schizophrenia data does include that year. To the extent that the weather in Ireland typically parallels the British Rainfall data mapped for Wales/West Midlands/Southwest England, the Jan–Mar rain would be expected to have been lower than average in 1941.