11 June 2015

Genes:

Different types of cells in the body do different jobs, but they are basically similar.
They all have a centre called a nucleus. Inside the nucleus are the genes.
Genes are really bits of code. The information they carry can be switched on
or off. The genes control the cell. They decide when it will reproduce,
what it does and even when it will die.

Normally the genes make sure that cells grow and reproduce in an orderly and
controlled way. If the system goes wrong for any reason, the usual result is that
the cell dies. Rarely, the system goes wrong in a way that allows a cell
to keep on dividing until a lump called a 'tumour' is formed.

Genes are coded messages that tell cells how to make proteins. Proteins are the
molecules that control the way cells behave. In this way our genes decide what
we look like and how our body works. We have many thousands of separate genes.

Genes are made of DNA and they are in the nucleus of the cell. The
nucleus is the cell's control centre. Genes are grouped together to make
chromosomes. We inherit half our chromosomes from our mother and half from
our father.

Genes tell cells how to behave. They control how our bodies grow and develop.
We each have about 25,000 genes. So far scientists have found around 300 that
play some part in the development of cancer.

Cancer cells are different from normal cells. They have changes (called faults or
mutations) in several of their genes which make them divide too often and form
a tumour. The genes that are damaged may be
•Genes that encourage the cell to multiply (known as ontogenesis)
•Genes that stop the cell multiplying (tumour suppressor genes)
•Genes that repair other damaged gene

Many gene changes that may make a cell become cancerous are caused by
environmental or lifestyle factors, such as smoking. But some people have
inherited faulty genes that increase their risk of particular types of cancer.
It is important to understand the difference between cancers due to genes you were
born with and cancers due to gene changes that have happened during your lifetime.

All cancers develop because something has gone wrong with one or more of the
genes in a cell. But most of these gene changes happen during our lives.
They happen as we get older or because of something we
are exposed to, such as cigarette smoke or sunlight. These substances, called carcinogens,
cause changes in the genes that make body cells more likely to
become cancerous. The gene changes don’t affect all body cells. They are not inherited
and cannot be passed on to your children.
The strength of your family history depends on
•Who in your family has had cancer
•How old they were at diagnosis

The more relatives who have had cancer, and the younger they were at diagnosis,
the stronger your family history. And the more likely it is that cancers are
being caused by an inherited faulty gene. According to cancer research
UK, you may have a strong family history if any of these situations apply to you
•More than 2 close relatives on the same side of
your family have had cancer (the same
    side of your family means either your father’s relatives or your
    mother’s relatives)
•They have had the same type of cancer, or different cancers that can be caused
   by the same gene fault
•The cancers developed when they were young, below the age of 50
•One of your relatives has had a gene fault found by genetic tests

Cancer is most common in people over the age of 60 and is rare in young people.
So cancer in older people is less likely to be due to an inherited
cancer gene.
Cancers develop from a single cell. This happens when there is a fault in one or
more of the genes in that cell. Usually a cell must have half a dozen or more
gene faults before it becomes cancerous. Scientists call gene faults ‘mutations’.
A gene mutation can make a cell stop working properly. It may become
cancerous and divide and grow uncontrollably. These changes can happen either by developing
gene faults during your lifetime or inheriting a cancer gene.

Most cancers are caused by gene faults that develop during our lifetime. There may be
a random mistake when a cell is dividing. Or the cell’s DNA may be damaged
by a carcinogen. A carcinogen is something that increases the likelihood
of a cancer developing – for example, cigarette smoke.

Some people have an increased risk of some types of cancer because they already have a
gene fault when they are born. They won’t necessarily develop cancer. But they are one step further
along the road to developing cancer than people without that gene fault.

Inherited gene faults that increase the risk of cancer are often in genes that repair mistakes in
other genes. The BRCA1 gene that increases the risk of breast cancer is a DNA repair gene.

The faulty repair gene doesn’t work as it should. So it doesn’t repair the other genetic
mistakes that we all gather as we go through life. In turn, this means you are more
likely to gather enough mistakes to cause a cancer at a younger age.

Because we inherit genes from both parents, you have a 1 in 2 chance of inheriting a
cancer gene fault that one of your parents has. The closer the relative, the
higher the chance of inheriting genes that they carry.

Generally, a cell must gather about 6 or so specific genetic faults before it becomes cancerous.
So being born with one gene fault doesn’t mean you will definitely get cancer.
You are at a higher risk than someone without that gene fault because genetically you are one
step further down the road to getting cancer. Doctors call this having a genetic predisposition
to cancer.

Different gene faults increase risk of different cancers. With a known gene fault,
your doctor may suggest that you need regular monitoring for particular cancers.

Some inherited cancer genes are more likely to cause cancer than others. This varies between
cancer genes. It depends on how big a part the cancer gene plays in the development
of that cancer. Many other factors need to be in place for a cancer to develop. People who
have the faulty breast cancer gene BRCA1 have a higher risk
of developing breast cancer than those with a faulty BRCA2 gene. So this tells us that the BRCA1
gene fault plays a bigger part in causing breast cancer than BRCA2. Because
the other factors are not always in place, ‘inherited’ cancer may seem to skip a generation.
A parent may have the gene and not get cancer, but their child who
inherits the same gene does. We need more research to find out what these other factors are for each type
of cancer. And how genes work together to cause cancer to know how
we can reduce the risk of developing it. Hopefully in the future we may be able to prevent
it altogether.

If you have a faulty gene your doctor may be able to give you an idea of how much your
risk is increased compared to the general population.