Studying biological vulnerability and heterogeneity--a long way ahead

Common diseases are usually the consequence of a variety of etiologies. This rule applies, for example, to mental retardation and epilepsy. There is evidence that genetic factors influence the propensity to utilize alcohol on an addictive basis at two levels of interaction between the drug and the body. It is doubtful that psychiatric symptoms are specific for defined etiologies. Individuals who are heterozygous for autosomal-recessive alleles may show slight deviations toward the homozygous genotype. These findings are applied to a polygenic concept of psychiatric disorders. Data are presented that would be compatible with a slightly increased incidence of heterozygotes for Wilson's disease and metachromatic leucodystrophy in psychiatric patients.