Explanation

[weegiz12345]

Hi

Can someone tell me if a person has been tested for ataxia and it’s positive , can it totally miss a generation without affecting anyone in that generation or would it mean someone was just a carrier of ataxia xx

[PatsyIpswich]

as far as I am aware yes. I'm no expert but I have listened to many Q&A Sessions.

[weegiz12345 in reply to PatsyIpswich]

When you say yes do you mean someone can just be a carrier. I have it, my son has just found he has it. We think my mums mum had it, mum shows no symptoms does it mean she carries the gene? Xx

[PatsyIpswich in reply to weegiz12345]

I meant yes it can skip a generation. It seems quite random. Ataxia UK helpline/research team can give you more detail. Take care 🙂

[weegiz12345 in reply to PatsyIpswich]

Thanks Patsy xx

[AbbeysAtaxia]

Hi,

Sorry to hear your son tested positive. Am I correct from reading your previous posts that you're asking about SCA2 (a dominant & repeat expansion ataxia)?

In general:

We inherit one two copies of every gene, one copy from each parent.

Dominant Ataxias: passed on by an affected parent via a variant in one copy of the gene. Usually adult onset conditions.

Recessive Ataxias: passed on by both unaffected parents, via two copies of a gene variant, one copy from each parent. Usually childhood onset conditions, but "milder" mutations can cause adult onset.

Repeat Expansion Ataxias like SCA2 are caused by 3-letters repeats in DNA such as "CAG" getting repeatedly copied (CAG, CAG, CAG to many CAG's), the larger numbers cause a big tangly protein that either doesn't work or is toxic to other processes in our nerves. The SCA2 CAG copy numbers work like this:

(1) 14-31 CAG's is normal (22 average)

(2) 33-34 CAG's onset usually aged 60+

(3) 35+ CAG's onset usually aged 20-60

(4) 45+ CAG's onset possible before age 20

The CAG repeat can get larger down through the generations, causing younger onset and/or more severe symptoms (called "anticipation").

However, CAG repeat size only explains 50% of age of onset, the other 50% of deciding factors for age of onset are currently unknown (genetic, enviromental, nutritional?). So even if your mother had the same variant, she may just not have got SCA2 yet (assuming she was the one who passed it on, not your father via an increase in CAG count and if your untested maternal grandmother had a different condition!).

So, your son's CAG repeat number will tell half the story, but only time will tell if and when he could get SCA2 symptoms.

Hope this helps.

[weegiz12345 in reply to AbbeysAtaxia]

Thanks for this, takes quite a bit of understanding, will keep reading it to try. Thanks for caring xx

[Tallguy101]

Hi as far as I know if one parent has the faulty gene there is a 50% chance of passing the disorder down to a child. However if both carry the faulty gene then it is very likely. I'm in the same boat, my son from my first marriage is 24 he has a 1/2 chance, so far he hasn't been tested...

[weegiz12345 in reply to Tallguy101]

Thanks xx