Family Data Concerning the Hypothesis of Hereditary Predisposition Toward Alcoholism

The hypothesis is stated that there is random genetic transmission of alcoholism within the sibships of alcoholics, regardless of possible environmental influences related to such objective factors as parental ages at birth, parental loss by death or permanent desertion, family size, birth order, ordinal position, sexes of siblings, and intervals between the patient and preceding and following siblings. A method of testing this hypothesis, with respect to family size, birth order and ordinal position, has been illustrated by extending the analysis of data on 110 male alcoholics previously recorded by another author. The corrected mean family size of 3.4 and modal family size of 1 are identical with those previously obtained by the present investigator for another sample of alcoholics. Empirically, a mode of 1 is not expected with a mean larger than about 2.6, and the corrected frequency of only children among both samples of alcoholics appears unduly high (over 25 per cent. of weighted frequencies in each instance). The goodness of fit between observed and expected frequencies of each birth order was such as might have been expected on the basis of chance about once in four trials. The observed frequency of youngest born from sibships having four or more members was at least twice that observed for either eldest, second born, or penultimate members. A deviation of this magnitude could have been expected to occur by chance only once in more than 15 trials. These findings suggest that the vulnerability of certain individuals to alcoholism is not determined solely by random genetic predisposition, and further more extensive tests of the initial hypothesis appear justified.