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I think there is a fine, but important, distinction between the terms "genetic" and "heritable". Many diseases and other non-disease traits, possibly even Parkinsons, may have a "genetic" basis. This means that a gene is involved in the expression of that trait. It does NOT mean that if you have the gene you will have the trait, even if it is a "dominant" gene. Many genes require an undefinable special environment for them to be expressed as a trait. This special environment may be the presence of other genes or some chemical (natural or unnatural) present at a particular time in development. This special environment may be something we have absolutely no control over - such as natural fluctuations that occur in the body during development. But to say that someone has a gene for something, that it is "genetic" or has a genetic basis, may say very little about one's chances of acquiring the trait. When some trait is described as being "heritable", it usually implies that some pattern of inheritance has been established. Thus one can reasonably determine the chances, or probability, of acquiring that trait from examining a family history. There is, to my knowledge at this time, no reliable and repeatable evidence that Parkinsons is heritable. I believe it is premature, and perhaps harmful because of the unnecessary fears it raises, for us to be discussing the "heritability" of PD. The "genetics" of PD is a question that will have to await the results of those searching for the genes involved, if there is one. And to date, there is no good evidence of this either. Is there any data regarding the percent of Parkinsons' offspring who never develop symptoms. I suspect it is very high. Allan Hansell