Mendelian inheritance or transmissible agent? The lesson Kuru and the Australia antigen.

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Abstract
In several human diseases familial environmental factors can be confused with a truly hereditary basis. In the case of Kuru and the Australia antigen, infective agents have proved to be responsible, and it seems probable that other human familial disorders may have a similar basis. An infective basis is not the only possible explanation for such effects; biochemical and immunological mechanisms are equally possible. In order to avoid confusing these effects with true Mendelian inheritance patterns several major points should be adherd to: vertical transmission of a disorder through several generations does not necessarily indicate dominant inheritance; a tendency to familial aggregation without a clear Mendelian pattern does not necessarily imply multifactorial inheritance; predominantly maternal transmission should raise the suspicion of an intrauterine or comparable environmental factor; the lack of a genetic basis may be irrelevant to practical considerations of genetic counselling.sbd. recurrence risk in a family may well be higher if the determining factor is environmental rather than genetic; and the existence of Mendelian inheritance does not exclude the operation of important environmental factors influencing the expression or transmission of the disease.