A small study reported on in this BBC article found it to be the case. However it was not clear how the sample of families was chosen, so it is hard to say how typical this should be considered to be. Still, the findings were strong enough to suggest that there is probably at least something to it, even if the all/nothing ratio suggested in the study may be overstated.
Article here: http://news.bbc.co.uk/2/hi/health/8144376.stm
Article here: http://news.bbc.co.uk/2/hi/health/8144376.stm
