Muscular Distrophy.. Genetics Q

[Aimz]

Muscular Distrophy runs in my family.

My uncle suffers from it and will probably be wheelchair bound within the next 5 years (he is 40). His is a chronic case and he is on constant pain medication and is unable to work. His symptoms began 10 years ago. The doctors who have done his genetic testing say that this particular strain is carried by females but it can only be passed on to males.

Based on this, it is likely that I am a carrier for the gene, and if I were to have a son, he would be at risk of suffering from the illness. My uncle is one of three boys, and he is the only one with the illness.

I could go and have some genetic tests done - but it wouldn't stop me from wanting a child.

The genetic information has only just been released and now I am worried about the moral dilemma I face when I start trying for a baby.

Has anyone else known they were a carrier to a genetic disorder and TTC anyway?

[sangie]

I wouldn't say that you are likely to have the gene - you will only have a chance of carrying the gene if one of your parents does. So in this case if your mother carries the gene then you may too, but not necessarily. Does your mother know if she carries the gene?

If you are carrying the gene then you may be able to have embryo screening if you wish and if it is available for this particular gene. Alternatively you may be able to do pre-implantation sex selection and choose to only have girls (although they may still be carriers unless you combine this will gene selection). Of course all these will be time consuming and there will be costs involved which I'm sure you are aware of. In the end you and DH need to make a decision on the potential risks for your children and do what you feel comfortable with.

I'm sorry about your uncle, I know somebody with MD and it is just awful. There is quite a lot of research being done on MD, in particular with stem cells. Lets hope that in the future it will be treatable!

[Aimz]

So let me get this right...

My Nan is a carrier of the gene and passed it onto my uncle. That they have established. She also passed on the gene to my Dad and my other uncle too - yet they haven't been affected by the illness. Does that mean that because she didn't have any daughters the gene stops being transferred?

Wouldn't my female cousins and I be carriers too and therefore be at risk of passing it onto our sons?

[sangie]

Ok sorry I get it now. It depends on the gene and there are different forms of MD which are inherited in different ways. Yep can get confusing. Hope this helps:

What Causes MD?
MD is a genetic disorder caused by a faulty gene that is generally inherited from one or both parents. Two thirds of all cases fall into this category. One third of cases, however, are caused by a faulty gene that is not inherited. This faulty gene mutates into an MD-causing agent of its own accord. Researchers do not yet know what causes the gene to mutate. Genes exist in pairs in the cells of our body. They determine how our cells form, grow and behave. Each parent contributes one gene for each pair. There are three primary ways to inherit a faulty gene from parents that may—or may not—develop into MD:

X-linked recessive inheritance
Autosomal recessive inheritance
Autosomal dominant inheritance

X-linked recessive
Each parent provides one sex chromosome to create the cell that becomes an embryo—an X chromosome or Y chromosome. Females have two X chromosomes, males have one Y and one X chromosome - the union creates either XX (a female child) or XY (a male child).

X-linked recessive inheritance is when the mother passes on one faulty X chromosome (See figure below). The resulting child, male or female, has a 50% chance of inheriting the faulty gene but only the male can develop MD from it. Because the female child has two X chromosomes, one healthy X can override one inherited faulty X. In this instance however, the female child is still a carrier of the inherited faulty X and may pass it on to her children. The female child should have genetic testing to determine her status before having her own children.

Autosomal recessive
This type of inheritance is when both parents carry - and pass on - a recessive faulty gene. A recessive faulty gene is one that does not display symptoms, so the parents may not know they carry it. Each of their offspring, regardless of gender, has a 25% chance of developing MD.

Autosomal dominant
In this case of inheritance, only one parent needs to pass on a faulty gene to affect their child (called a dominant gene). This faulty gene can come from either parent and can affect male or female children. The child has a 50% chance of developing MD.

[Aimz]

X-linked recessive inheritance is when the mother passes on one faulty X chromosome (See figure below). The resulting child, male or female, has a 50% chance of inheriting the faulty gene but only the male can develop MD from it. Because the female child has two X chromosomes, one healthy X can override one inherited faulty X. In this instance however, the female child is still a carrier of the inherited faulty X and may pass it on to her children. The female child should have genetic testing to determine her status before having her own children.

Ok so this is the one that runs in our family. So there is a 50% chance that I carry the gene - that is what I thought.

So if I am tested and it is proven that I carry the gene, then there is a 50% chance of passing on that gene to my son who could then become sick with the illness later in life. Is that right?

I looked up the gender selection/IVF and you obviously have to qualify to be able to have this done (in some places they have canned it all together). Even then - isn't that majorly messing with mother nature?

On the flip side though - if I chose not to get tested and went ahead and concieved a boy, I would have knowingly put that child at risk.

[sangie]

Yes your children have a 50% chance of inheriting the gene from you but only your son would be affected by it. If I was you I would probably get tested and then worry about the implications if you need to...........cross one bridge at a time!

If you carry the gene defect then it would be really worthwhile seeing a genetic counsellor - they will be able to tell you all about your options and answer your questions much better than I can! As for messing with mother nature - well that is a decision you have to make and a genetic counsellor will help you with that. It's not uncommon in families who carry serious genetic disorders. Alternatively you may be able to screen for the gene irrespective of sex, thereby choosing not to implant affected embryos. Not saying you should do this, but these options are available.

[Aimz]

Thanks so much Sangie. I'm seeing my GP tomorrow so I might mention it to him then.

My guess is the genetic testing is going to be majorly expensive too *eek*.

[sangie]

Good luck Amy!

Not sure about the cost. Might just be a cheek swab hopefully, nice and easy!

[HotI]

Hi Amy

Sorry for more questions, but just want to check on something. Has your Dad actually had the genetic test and been told he has the same mutation (gene variation) as your uncle?

Your Nan is a carrier, but she has two X chromosomes. She passes one X chromosome on when she has a child. (And the man passes either an X or a Y, so the baby then has XX or XY). So, for each of Nan's children, they have a 50% chance of having the X with the mutation.

If your Dad hasn't had the genetic test yet, this will change your risk figure (that you are a carrier) to 25%.

Also, if the family mutation is known, a woman may be able to have PGD and select only babies that do not have the mutation. This could still be a boy, just carrying the 'healthy' X. It all depends on which gene is involved and if they can make a genetic test that will work on only one cell (which is how PGD works).

I read your other post, and i am glad you are feeling a bit better. If this post is overload, feel free to ignore it and come back when you are ready.

take care,

kate

[Aimz]

Hi Kate,

When my uncle started his testing 12 months ago, my Dad, other uncle and Nan all had bloodwork done as well. It came back that all three boys have the mutated gene, however only one has been affected by the disease. As I have previously said, that is not to say my Dad won't get the illness when he is in his senior years. So my risk of being a carrier is 50%. I probably should have clarified this earlier.

Thanks