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One hundred and ninety subjects from 100 adult polycystic kidney disease (APKD) families on the North Western Regional Genetic Register were interviewed to determine the likely demand for prenatal diagnosis. A detailed questionnaire was used to assess understanding and experience of clinical, therapeutic, and genetic aspects of APKD. Major features of the disease (presence of renal cysts which can lead to renal failure) and forms of therapy (dialysis and transplantation) were known; knowledge of less common features was related to experience. The cohort had had genetic counselling and the majority knew the risk to their own offspring, although the mechanics of the mode of inheritance was often misunderstood. Uptake of presymptomatic ultrasound testing was high, and some implications of early diagnosis are noted. A minority changed their reproductive behaviour as a result of APKD, and although the majority felt a prenatal test should be available, only 23% at high risk of passing on the disease and contemplating children felt they would be interested, and so far only one request for prenatal diagnosis has been received. Thus, demand appears to be low and to be related to perception of the seriousness of APKD.

Twenty-four families with adult onset polycystic kidney disease were typed for markers flanking the PKD1 locus on chromosome 16. The aggregated results gave a significant lod score in favour of linkage to PKD1. Within this group of families two showed unusual features: recombinations, including double recombinations, and, in one family, an unexpectedly high proportion of affected people. We consider the evidence that in these families the disease might result from a mutation at a different locus, PKD2, not linked to PKD1. We suggest that a useful test is to compare the relative numbers of meioses apparently non-recombinant and doubly recombinant for markers flanking the normal disease locus, ignoring meioses recombinant for only a single marker. Using this test, neither our two families nor the data published so far on other families provide compelling evidence for the existence of a second locus for adult polycystic kidney disease. For genetic counselling in families too small to give internal evidence for or against linkage, the extra uncertainty can be handled by using a higher recombination rate.

A recent report from the Departments of Health draws attention to the value of DNA diagnosis for inherited diseases and the need for planning these services in the National Health Service. There is great potential for preventive medicine, but a major immediate benefit is the newfound ability to exclude the carrier state in many people at risk and to protect fetuses from abortion when, as in most cases, they are shown to be normal by DNA tests. However, the widespread application of these new techniques requires prior evaluation and general acceptance. This will only be obtained after public debate, education of professionals and the population, and the establishment of adequate non-directive genetic counselling services. Some of the points to be considered in setting up molecular genetics laboratories are described.