[Gozoman]

Gozoman  asked the Naked Scientists:

First of all can I say just how much I enjoy the show. I download it to my MP3 player and listen to it in work. You guys keep me sane!
 
My aunt has three kidneys and her heart is on the opposite side. She is in her late 60's now and quite healthy. Is this sort of thing rare? Is it possible that twins had started to develop and then something happened and they merged into one?
 
Thanks guys and keep up the good work. I will be listening to a few shows on my flight to Malta next month which should make the time fly in!
 
Alex Tyrrell

What do you think?

[RD]

Having the heart on the opposite side is called "Dextrocardia".
The incidence of dextrocardia is about 1:10000, (there are different types).

When when all the organs are reversed it is called "Situs inversus", which is rarer.

These are genetic conditions, not caused by the merging of twin embryos.

The incidence of extra (supermumerary) kidneys is described here as "relatively rare".