Inbreeding and schizophrenia

The unique situation that the Norwegian 1891 census included information on consanguineous relation between spouses and that first admissions to psychiatric hospitals by diagnosis were available for the years 1921‐40, formed the basis for the present study. There are similarities between the pattern of inbreeding and admission rates in our rural communities, but we were unable to demonstrate any significant correlation. This is interpreted as due to selective avoidance in the choice of a marriage partner, particularly between near relatives. Good neighbourhood knowledge was an important factor in our sparsely populated communities with a marriage pattern distinguished by extreme geographical proximity of residence of spouses.The considerably lower proportion of first cousin matings than expected among parents of psychiatric in‐patients 1926‐55, illustrates the lower psychiatric morbidity in offspring of consanguineous parentage.Admissions 1921—40 comprised only functional psychoses with a predominance of schizophrenia (> 80%), which today is diagnosed in less than 10%. A decline in incidence rate is not likely, whereas changing diagnostic practice is probably a main factor. The