In the Galapagos, I think
Swimming with penguins
Frolicking and imbibing over the holidays have left me so
far behind in combing the Web for interesting cancer news that I would need at
least two Research Assistants to catch up before next Christmas. So, next best thing: I plan to make good use
of the old Delete button. But here is
one (from 12/22) that needs to be discussed.
Here is the Web address:
It is short and easy going, so take a look.
The research was done at Washington University School of
Medicine, in St. Louis. The question
addressed was: What fraction of various kinds of cancer are owing, at least in
part, to heredity? What demanded my
attention was a graph showing these fractions for 12 common cancer types. Right up there at the top of the graph was
ovarian, at 19%!
The work made heavy use of The Cancer Genome Atlas, which we
have discussed previously. See, for
instance:
Let me nutshell the article.
The study used people known to have one of twelve common cancer types. The “sample” is reported as “more than 4000”. The methodology involved comparing “germline”
genes (what you are born with*) with the genes expressed in the tumor cells
themselves. Some mutated genes are well
known to be implicated in cancer; your old friends BRCA1 & 2 for instance,
or a particularly nasty bastard called RAS.
If a disabling mutation was present in high quantity in the tumor, and
also found in germline cells, the tumor was classified as hereditary.
But what, you shout, about the same gene from the other
parent? Well, if both parents contribute
the same defective gene, the poor offspring is – it seems to me – toast. Likewise if the mutated gene is strongly
dominant, toast again – although this raises the question of how the parents
remained alive themselves. But most of
the time there will be one functioning gene to provide the proteins that keep
cancer in check. The problem arises as
time and repeated duplication of DNA invite mutation. If you have one defective gene, and then a
random mutation puts the other one out of commission, then – well, heck, toast.
You probably noticed that this was a pretty big nutshell – a
coconut, for instance. So, enough. Stop reading here, unless you’re a masochist.
Okay, game for more, eh?
If you read the article you probably will stumble over the term “truncation
mutation”. As you are aware, DNA is “transcribed”
into RNA, which then interacts with a tiny protein-manufacturing plant to
produce the proteins upon which all life depends. DNA (and RNA) are said to “code” for the amino
acids of which proteins are composed.
The code is “triplet”: three consecutive nucleotides indicate a unique
amino acid: for instance, UAU codes for something called
tyrosine. There are also combinations
that tell the little protein plant (it’s called a ribosome) when to stop. So let’s say that the ribosome is chugging
away and encounters a codon that should read UAU but, because of a mutation,
actually reads UAG. UAG is a STOP codon –
it tells the ribosome to stop synthesizing the protein and kick it out into the
cell. The protein is thereby “truncated”,
and furthermore, useless.
Now wasn’t that fun?
*This germline-sampling stuff makes me cringe. You know where germ cells are stored, right? Do
they use a needle to get their sample? I
hope not
Another article describing this research:
ReplyDeletehttp://www.medicalnewstoday.com/articles/304434.php
Shorter and even easier to digest..