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Old 05-02-14, 11:26 PM   #11
DH
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Default Re: CAG count...

Quote:
Originally Posted by Shelli View Post
When my son was tested they said the cag count didn't matter because there was no definitive proof that enabled them to tell me when he would develop it regardless of what I might read etc. it's making me paranoid :( x
Really? That's strange. As far as I can tell (based on talks with Dr Barker at Addenbrokes Hospital) if your CAG count is over around 40 you WILL develop symptoms at some point in your life.

As per Allans info there is a grey area around 36-39 where you may or may not develop HD. My guess is you may die of old age before it takes hold? So yes, the actual numbers are important, but only in as much as they say whether or not you will develop the disease. Everything else, such as age of onset, is in the hands of chance.

DH, CAG count 40
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Old 06-02-14, 12:18 AM   #12
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Default Re: CAG count...

I hope nobody minds me putting this here [wrong thread, I know] but as we are discussing CAG counts and we have several recent newcomers to the board I thought it might be useful to enlarge on CAG counts. If you read this you will probably be better informed than your GP.

What causes HD?

HD is caused by a mutation in a person’s DNA. Your DNA is basically lots of instructions for building your body and keeping it running. DNA is organized into individual ‘recipes’ called genes. Each gene is a recipe for one protein [a molecular machine]. A mutation in a gene is like a spelling mistake. Some spelling mistakes are harmless, but some result in proteins that don’t work properly or are harmful.

The mutation that causes HD was mapped to a specific gene in 1993 - this gene is now called the ‘huntingtin’ gene, and is abbreviated as ‘HTT’ or ‘HD’ or ‘IT15’. Knowing the location and nature of the HD mutation has allowed people to be tested for the HD mutation since 1993.

So what’s all this about ‘CAG’?

Everyone with HD has the same basic type of mutation. It is an expansion of a normal repetitive piece of DNA on chromosome number 4. Chromosomes are long pieces of DNA which are chains of millions of ‘bases’. Each base is like letters of the alphabet spelling a word. Every base is one of 4 chemicals [Cytosine, Adenine, Guanine, Thymine]. These bases are abbreviated as C, A, G or T.

Near the beginning of everyone’s huntingtin gene is a repetitive stretch of three letters - CAG. In people without HD, these three bases are repeated fewer than 35 times - usually about 17 times. People with 36 or greater repeats of CAG will develop HD if they live long enough.

Each person whose parent has Huntington’s disease is born with a 50-50 chance of inheriting the faulty gene. Anyone who inherits the faulty gene will, at some stage, develop the disease.

A genetic test is available from specialist clinics throughout the country. This test will usually be able to show whether someone has inherited the faulty gene, but it will not indicate the age at which they will develop the disease.

How does an expanded CAG repeat cause Huntington’s disease?

Proteins are made from building blocks called amino acids. The three-base sequence CAG in a gene is an instruction to add an amino acid called glutamine to a growing protein. How ever many CAG repeats there are in a huntingtin gene, is how many glutamines will be in the finished protein. So, for example, people with 42 CAG repeats produce a huntingtin protein with 42 glutamine blocks at the start.

Scientists have abbreviations for the different amino acids. Glutamine is abbreviated as ‘Q’, so Huntingtin’s disease is sometimes called a ‘polyglutamine disease’ or a ‘polyQ disease’.

When the huntingtin protein contains too many glutamine blocks, it has a different shape from the normal protein, and behaves differently too. These differences cause the abnormal protein to become harmful to cells, and it’s this harmful behaviour that causes cells to malfunction and die.

Malfunctioning and dying neurons [brain cells], and other cells, are what causes the symptoms of HD.

The average CAG repeat length in HD patients is about 44. It’s important to note that the ability to predict age of onset from CAG repeat length is not at all accurate. Two people with the same CAG repeat length might start to experience symptoms at very different ages - many years or decades different. Because of this, CAG-repeat lengths are useful for scientific and medical research, but aren’t very informative for most people trying to predict their own expected age of onset.


I have a more complete version - if you want it send me a private mesage.
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Old 06-02-14, 11:15 AM   #13
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Default Re: CAG count...

That is written very well. Thank you
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Old 06-02-14, 04:14 PM   #14
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Default Re: CAG count...

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Originally Posted by jacqueline View Post
Thank you
Good explanation Allan but it does sound complicated.
When Ed Wild explains at the AGM it makes it easier to understand to the untrained eye.
Ed Wild, Jimmy Pollard and others only appear annually for the few who can get to the AGM. In the meantime I just feel that the more we read on a regular basis the better we will understand - and become empowered, ie to talk on even terms with GPs, Adult Social Care, MH people ......... and to understand the HD Specialists at Clinical appointments.

If you were to read the original stuff - now that is difficult to follow:
http://www.nature.com/scitable/topic...ery-of-the-851

1993 Research report: A Novel Gene Containing a Trinucleotide Repeat That Is Expanded and Unstable on Huntington’s Disease Chromosomes http://deepblue.lib.umich.edu/bitstr...2AA?sequence=3

1993 New York Times report on the above: http://www.nytimes.com/1993/03/24/us...s-illness.html

Typical Ed Wild HD Buzz report: http://en.hdbuzz.net/023

What I try to do is find relevant stuff that I can copy and paste into my own documents - so that I can read them at my own pace and level of understanding. Many information leaflets are written from the outside looking in. What we need for those in our care is vitally relevant stuff written from the inside, from what we know and have learnt over the years from being in total contact with sufferers of HD.

My hope is that we can use our collective expertise [knowledge of Caring, etc] to work in a meaningful way with the professional experts. Some of us do that now but the empowerment through relevant reading will give us all the strength to make our mark.

Apologies for being a bit on the heavy side. S has decided not to go to another rearranged medical appointment - so I am ever so slightly ...... UPTIGHT WITH IT ALL.
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Old 07-02-14, 04:14 AM   #15
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Default Re: CAG count...

All vey true Jacqueline and Allan..
sorry you are feeling stressed Allan, it is so hard once they have their stubborn bouts.

I too would not have survived without this board.
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Old 07-02-14, 06:31 AM   #16
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Default Re: CAG count...

Hi Allan

As we are off at a tangent !

My daughter studied science and she advised me as I did not even have a GCSE in biology to my name to start reading BBC Bite Size to start working up to a bit more of an understanding.

The difference between a doctor and an A level student is probably six weeks of intensive reading per topic ! Apologies to any medically trained people reading this.

Do you recall the film called Lorenzo's oil where the couple actually outstrip the existing medical field because they are so motivated to find a cure ? That probably resonates with me.

I do agree that Ed Wilde does have a gift for explaining the science in a very clear way for families. Anyway I do not pretend to understand much but I have read lots more popular science books than I'd have ever done without this wonderful disease.

Dolphin
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Old 10-02-14, 04:09 PM   #17
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Default Re: CAG count...

[1993 Research report: A Novel Gene Containing a Trinucleotide Repeat That Is Expanded and Unstable on Huntington’s Disease Chromosomes http://deepblue.lib.umich.edu/bitstr...2AA?sequence=3

1993 New York Times report on the above: http://www.nytimes.com/1993/03/24/us...s-illness.html

Typical Ed Wild HD Buzz report: http://en.hdbuzz.net/023]

Thank-you for posting the scientific papers - I learnt a little bit about genetics during my masters and was wanting to get more detailed information - it still goes over my head, but I do find it helpful to understand a bit more about what is going on (as I've only just found out about having HD in the family).

Thanks,

Scabious
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Old 24-07-14, 12:31 PM   #18
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Default Re: CAG count...

hi shelli i got told my cag count
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