Why am I the short fat one?--The Secret Life of Twins

This change in the particular genes we express is controlled chiefly through a process called "methylation" in which chemical groups are attached to the DNA molecule to tell the body whether or not to use the "methylated" genes.

It is one of the ways in which our bodies' attempt to adapt to changing environments.

Twins play a key role in discovering more.

In the summer of 2009 Chris and I joined the twin research study at St Thomas's Hospital where we were investigated in great detail.

They measured our height, weight, bone density, grip strength even ability to hear if a nursery rhyme is in tune.

All these are traits that are to some extent genetic.

Other differences

It turned out that we are different in more ways than height.

For a start I was 15kg heavier than my brother.

"What about my missing 20mm of height? It is probably an epigenetic effect caused by some long forgotten environmental difference when we were little "
 
Of the thousands of twins enrolled in the research program only 10 were more different in weight than us.

Professor Tim Spector who leads the research unit was frank: "You're (he meant me) a disgrace."

My excess weight, unlike my brother's excess height, is easily explained.

I have been living in America and eating too much. So far no surprises.

But environmental exposure to a lot of cheap, high-fat food in America may have caused more than temporary weight gain.

It may have permanently altered the way my genes are expressed.

Scientists are only just beginning to understand these processes but it is possible that I may have permanently altered my metabolism to accommodate those extra pounds: the health effects could last a long time.

Key role in disease

Epigenetics seems to play a role in a large number of diseases.

Twins studies show us that some cancers are not caused by DNA mutations but by epigenetic changes, which potentially offers new targets for drugs.

Similarly with heart disease or diabetes we might one day be considering therapies that change our epigenetics.

This is a long way off but twin studies are beginning to shed new light on how our bodies react to the environment.

What about my missing 20mm of height? It is probably an epigenetic effect caused by some long forgotten environmental difference when we were little.

I will never get it back but if it is of use to medical science I can live without it.

(Edit:Ruby)