On effects of relaxed selection in familial disorders.

Theoretical predictions are made of the effect of improved treatments, with consequent increase in fertility of affected individuals, on the frequency of familial disorders. Multifactorial inheritance and some two-locus models are considered. (Changes for simple Mendelian disorders have been estimated previously by many authors.) It is estimated that, with two-locus or multifactorial models, an increase in frequency per generation of not more than a few per cent of the frequency of a disorder may be expected. The greatest increase will be in the first generation following introduction of the new treatment.