Is religiousness a genetically heritable feature? I know that parent beliefs have very strong influence on child, but is it possible that genetic factor also play a role? I doubt that the content of any religion could be heritable through genes nor anyone could be genetically predestined to be Christian, Jew, Buddhist or votary of any particular religion. But is it possible that some kind of sensitivity to religious aspect of life could be heritable? 

I know that it is hard to distinguish genetic and environmental factor in such case, but maybe someone have already made such research for example on monozygotic and dizygotic twins or adopted children? 

I've thought that if it is indeed heritable, then celibacy in the Catholic Church might be suicidal for this faith, as it eliminates the (potential) "godliness genes".
Monozygotic twin studies are the general course of action for this kind of question. Genetic and environmental influences on multiple dimensions of religiosity: a twin study concludes there is a genetic component. 

A complete approach for these kind of studies is to take twins that have been separated to different households from birth and compare them to twins in the same household. I'm not sure what this particularly study does (haven't read it) but its a typical approach in behavioral biology.

A summary of the above article, also references a book where they compared monozygotic twins to dizygotic twins.

The difference between monozygotic and dizygotic twins is that monozygotic twins share almost a complete set of genetics (mutations happen) while dizygotic twins share the same amount as a normal set of siblings.  The idea being that if monozygotic twins share traits at a higher statistical rate than dizygotic twins, that there is a genetic component to that trait.  This, of course, does not mean the trait "is genetic" in totality.  Most behavioral traits have a combination of genetic and environmental (be it developmental, social, toxicological, or else wise environmental) factors.  There's also a new factor discovered recently that lies somewhere in between: epigenetics.  I can't be certain, but I'd think this would appear in monozygotic similarities, probably confounding results a bit.