LouLou, I am puzzled by what you have been told.

In general, genes which are strongly associated with a disease come in two classes.

In one class the mutant gene encodes a protein which has gained an abnormal (pathological) function. These diseases are very rare and show a strong familial pattern - a child of a parent with one of these diseases has a 50% chance of inheriting the mutant gene and so will get the disease. This does not seem to apply to you and your sister.

In the other class the mutant gene encodes a protein which has lost its normal function. Somebody with one copy of the mutant gene and one normal copy will be fine because the normal gene copy ensures that they have the normal form of the protein. People like that are "carriers" of the disease. These diseases are relatively common.

Cystic fibrosis is an example - somebody may develop it if both of their parents are carriers. Cystic fibrosis occurs when somebody inherits the mutant form of the gene from both of their parents - there is a 25% chance of this happening.

Hi LouLou

If you search: "Hereditary sensory and autonomic neuropathy" there is a Wikipedia page with some info that may be of use.

I also came across this site which helps explain how genetic variations can occur or be passed down.

What are the different ways in which a genetic condition can be inherited? - Genetics Home Reference

Hope you can get some explanation of the genetic connection.

Thank you bluesfan that is very helpful information.

LouLou, I think that the link from bluesfan is excellent - it is well worth a read.

Geneticists use the word "penetrance" to explain how likely it is that inheriting a particular form (an "allele") of a gene leads to a health problem. In the single-gene diseases that I mentioned above, penetrance is often high (close to 100%) but these diseases are very much the exception, not the rule.

In most diseases inheriting alleles of many different genes are usually risk factors. This is very complicated; for disease X inheriting allele 23 of gene A might be a negative risk factor. This might be made worse in somebody who has inherited allele 45 of gene B but better if they have inherited allele 14 of gene C, and so on.

I don't know any examples in which sorting out these complicated patterns has led to improved therapy/treatment but this could change.

Now, cutting to the chase for you and your sister (all that I am concerned about here), you wrote:

"The neurologist she has just seen has told her that it is pointless going to get the biopsy done as there is nothing they can do about it as it will be hereditary."

Bluntly, this is nonsense. The neurologist may or may not be a good clinician but s/he knows slightly less than nothing about genetics.

It is what is called genetic determinism - "OMG, it is in my genes. There is nothing that I can do. I am doomed.". With the rare exceptions of single gene diseases, genetic determinism is a total myth.

One-line summary; if you (with confirmed SFN) or your sister (with possible SFN) decide to have children then go for it. Your genetics (and those of your partners of course) mean that your children are unlikely to be at greater risk of SFN than any other children.

Thank you so much Kiwi, that does make sense. I had been offered IVIG, I have a really good neuro who thought mine is immune mediated or a sub type of Guillian barre. My sister spent 5 minutes with that neuro, who I believe just fobbed her off saying " well we can't do anything for SFN, we can give you the pain meds now, you don't need to bother having the biopsy as if it comes back positive its hereditary so there's nothing we can do" . I have two small children and my sister has a daughter, so we were both left a bit worried after . Thank you to both and Blusfan, good job there are people like you on this site

So if both my parents were carriers and had had two children that both developed the disease is this possible? I mean if we were both the unlucky 25percent? Kiwi do you think it is more likely that this is due to some sort of exposure? Her neuro is rubbish. I can't believe he said it is pointless to get the biopsy. However he agreed to let her have it. Do you think it would be possible to pass on to my children? Thanks for your help kiwi