I have always wondered about this.
In my husband's family more are affected by HD than not. For instance,
of his aunts and uncles 3 out of 4 had HD. His first cousins, 4 out of 5 have gotten HD. In his own family so far 4 out of 6 have HD - the other two are younger and hopefully will not get it.

In going to a HD clininc we met a family in which 1 out of 9 children had HD, the others did not. My brother has an employee in which 1 out of 6 children had HD, the others did not. A friend of theirs has a mother who had HD and her siblings did not.

How does this work where some are very predominantly HD and others are not?
Do either of these scenarios usually change with more generations?
Do new generations get the symptoms earlier than their past generation?
If a generation gets HD in their 40's for instance, does the next generation normally get their symptoms in the 40's?
I know it all depends on the CAG count - I just wondered if the CAG count fluctuates one way or the other as time goes on?

Thank you for your input.

Funnily enough I was having part of this conversation just a short while ago. I was told that the daughter who inherits HD from her father will become symptomatic earlier than he did. I don't know if there is any truth in it, but the person I was talking to wondered, if that was true, then over time would it wipe out HD in that line?

What I have read, on many different sites, is that mother to child transmission results in the child (if positive) getting onset, on average at around the same time as the mom. From the father, hoever, it could come sooner or the same time.

Nothing to date makes one family more prone than another. If you could see all families I would guess most hover around the 50% mark. Where two or three out of 5 will receive the gene. Luck of the draw will make some be hit hard and others hit less.

CAG counts speak in generalities as to onset. There are exceptions to every CAG tendency. CAG and onset only speak to the population as whole. Not to individuals so you can count on nothing really as an individual. Most people who wear seat belts survive an accident. But that doesn't mean everyone who wears one will. You wouldn't want to guess ahead of time and go looking for a crash to have just because you will probably survive. You can't plan on surviving. Same with CAG counts. You can't depend on the tendencies applying to an individual or a family.

Marsha just put up something on lighthouse about gender to gender tendencies. I will look for that later. Can't remember enough to comment on it right now...

Here it is... [www.hdlighthouse.org]

It's true that age of onset seems loosely tied to CAG repeats - but there are exceptions.

It also seems true that transmission of the HD gene through the male parent is more likely to result in the increase in CAG repeats (and thus often earlier age-of-onset) than when transmitted through the mother. Marsha gives a far better explanation for the possible reason for that than I could ever give!

Miznjoe makes a very good point that there can be no truth to the conjecture that age-of-onset necessarily decreases with every generation. Obviously, if that were the case - the disease would wipe itself out of its own accord, since eventually everyone would die of it before they were of age to procreate.....

Isn't is true the HD is a dominant gene, like brown eyes to blue? So wouldn't the chances but just like a couple where one had brown eyes and the other had blue? Sometimes the couple would have two brown eyed kids but then have one blue eyed kid? Am I wrong about this? I swear I read this somewhere when I was a kid- cause I think someone said it's like guessing that my parent's third child would be blue eyed??

The main thing to remember is this... no matter your take or remembrances on genes, that the HD gene is dominate and that someone with HD carries one gene from each parent. They pass on one of those genes to the his/her child. If it is the mutated gene it will be expressed. So the odds are each child has a 50% chance of getting the gene.

I think what you are looking at is probabilities. That is like multiple coin flips. Each coin flip has a 50% chance of landing heads or tales. Probability says that given enough flips half the flips will be heads and half tales. But that doesn't mean every other flip will be heads. There are runs of flips where there will be three or four heads in a row... and later on there will be runs of flips that will be tales. So eventually it will even out and hover at 50%.

I have two children at risk. Each has 50% chance of having the gene. Probability say that between the two of them I have a seventy-five percent chance that one of them has the gene. Had I had more children, I believe at four kids, I have statistically assured that one will have the gene. But those statistics don't always hold true on that small a sample.

Shar, I surely would like for this subject to become a 'sticky'. On this forum we deal with reality - not just statistics.
No doubt there are hd-predominant families. In mine there were six in a row: both my daughters have hd; the oldest has a CAG of 43, and the youngest has a CAG of 40. In my uncle's family the youngest eight had/have hd. In both families, the oldest three do/did not. I am the youngest at 71.
Sounds logical that the hd-predominant families would die off. Evolution? Are large hd families becoming an oddity?
The huntingtin's gene is mysterious.
Statistically, succeeding generations have larger CAG counts. Lessor CAG counts are uncommon.
Bob

An interesting question, Bob! I've heard the conjecture that HD families tend to be large. That was certainly true in my case.

It makes no sense to me, actually. A friend of mine didn't scoff at the notion. He thought that genes of all sorts might have a primeval compulsion to propagate themselves.

Heck if I know!

Here is a new theory on why an HD family may be bigger. I have no opinion to it being valid. But it's an interesting thought.

[www.medicalnewstoday.com]

It is interesting. I have in fact been surprisingly healthy, all my life, aside from the HD.

I would have had children with my first "ex". He was apparently unable to.

Once I found out that I was fertile - with my second husband (because I miscarried) - it was about the time that I belatedly disovered that my dad had HD. I said, "OK, fine! The world doesn't need MY genes in the gene-pool! So I had myself fixed."

Eric,

Thanks for the link. That was an interesting article.

Terrific article. I sent it to my neice Fiona because I had told about it earlier. Her mother who did not have HD got cancer.
I'm writing my web.
Dusty

Having at risk kids I have looked to see what I can determine about hard hit families. There is nothing I can find that makes one family either harder hit or lesser hit but blind luck. There are two possible genes to be passed the normal and the HD gene. There is nothing that suggests the HD gene behaves differently in one family than another one. My wife's family is like yours Bob... not many escapees lately. There is just nothing but chance to explain that tho. DoubleJ just stated both her children tested negative thank goodness. It was chance in their case too. I prefer not to feel cursed if there is no good reason to do so. Some things in life come down to pure chance. It's hard to accept when you want an explanation... easier when you need hope.

Like Eric, I have researched the "why" of who gets HD and who does not. There is no explanation. In Gene's family, his mother and all her siblings had HD. Gene's sister now has HD and he has two brothers that do not show any symptoms. His aunt who contracted HD after she was 60 had two sons, both of them have HD. Another aunt with HD had four children and none of them show symptoms and they are in their late 40's early 50's.

In my children's case, they were both convinced they had HD. Every time they bounced their legs when they were seated or got angry, they knew it was HD. Ever since I learned what HD was and that the children had a 50/50 chance of having it, I dreamed of a day when they would tell me they were both negative or the day that a cure would be found. I still find it hard to believe that my dream came true and my prayers were answered.

My heart breaks for those that have children at risk or have children with JHD. This disease does not discriminate; it crosses every religion and ethnicity.

Hope is the most important four letter word we have. We hold onto the hope that therapeutics to stop the progression of the disease or a cure will be found for the children.