EXPECTED EFFECTS OF MASS-SCREENING POLICIES ON THE FREQUENCY OF CYSTIC-FIBROSIS HOMOZYGOTES

We evaluated, by deterministic computer simulation, some effects of a screening programme for carriers of cystic fibrosis mutations. Two dif ferent selective regimes (heterozygote advantage and directional selec tion against recessive homozygotes) and three kinds of response to the screening were simulated. The curves describing the expected decline in the frequency of CF homozygotes allow one to predict some benefits of a screening campaign. In addition, it is shown that a strategy aime d at testing couples, rather than individuals, may become less expensi ve after only two generations of screening. The main source of uncerta inty for a screening programme remains the selection mechanism, namely the existence of some sort of biological advantage for heterozy,gous carriers of CF mutations.