ABSTRACT
This chapter provides particular families in which a genetic disorder exists or is at risk of occurring. X-linked disorders seem at first sight to be a suitable area for prevention in the population, and certainly the testing of the extended family for carrier status is probably one of the most valuable parts of genetic counselling. X-linked disorders where fetal sexing used to be employed without a direct prenatal diagnosis might have provided an important example of where genetic measures could increase the population frequency. The genetic risks for couples in particular situations have already been discussed, but worry is sometimes expressed as to the overall effects of such assortative patterns of mating on the population level of the particular condition. There has been a succession of developments in screening for genetic disorders in pregnancy that have cumulatively had a major impact on the way in which pregnancy is managed and perceived.
