Tuesday, January 01, 2008

Un-Methylated Spirits

Our 'nurtured' genes determine who we are. Our DNA gene codes for an RNA message that gets printed out into a string of protein that gets folded up in three dimensions to become a little bit of bio-nano-technology. This is why we are tall or short, fat or thin, blue-eyed or brown.

You would think that it would not matter if a chromosome comes from your mother or your father- that there would be no way to tell- after all they simply consist of chunks of DNA. Female mice have 2 copies of their X chromosome- but it is ALWAYS the paternal X that is switched off. This 'tagging' is known as genetic imprinting- and the trick is performed using methylation.

There are 2 "epigenetic" syndromes that are essentially the reverse of each other- both are due to problems with genes on an area of chromosome 15.

Prader-Wili syndrome occurs when neither segment has paternal imprinting- (e.g. the mother's contribution is present, but the father's has been deleted). These children are characteristically obese, hypogonadal and have some intellectual impairment- although interestingly tend to be very good at jigsaw puzzles!

Angelman's Syndrome occurs, by contrast when there is no maternal imprinting present (e.g. the father's contribution is present, but the mother's has been deleted). These children were initially described as "Happy Puppets". They are often affectionate, verbose, and crave human contact.

But there is more. Genes can be tagged "maternal" or "paternal"- but methylation occurs for many other reasons too. A diet high in "methylation" precursors in rats can change the expression of a lot of genes.

Here is the REALLY interesting bit: If methylation occurs in the cells destined to become the sperm or ova- then these traits become hereditary- at least for a few generations. In other words, this represents a form of "Lamarckian" (vs Darwinian) evolution- the inheritance of acquired characteristics.

Offspring of female rats fed folic acid had brown fur due to methylation of the Agouti gene. Offspring of rats who were not fed the supplements had yellow fur- AND a tendency to diabetes and obesity!

You are not what you eat- you are what your mother ate! It makes me wonder- what if the folate supplement that reduces the incidence of neural tube defects and leukemia in our children has more sinister late methylation effects?

What would a genetically normal but completely un-methylated human look like?

Detailed article here, New York Times article here.


  1. NICE Blog :)


  2. wow that was quick- i just hit "publish".

    Happy New Year!


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