A question for tamum or anybody else who knows about genetics

[emkana]

To dive straight in:

If a syndrome is autosomal recessive does that mean that it can only be passed on because both parents have the defective gene? Or is it always a possibility that it's a case of spontaneous mutation?

Just musing about the odds of having a baby with Jeune's when dh and I are from two different countries, and already have two healthy children...

The baby has to have two copies of the recessive gene. In many cases this is because both parents are carriers. Spontaneous mutations can also occur but I would imagine that these are rarer than a parent being a carrier and for both genes to have mutated would be rarer still....but Tamum and blue know more than I do

mb has said it all really- I don't know of any cases of spontaneous mutations for recessive disorders, but that doesn't mean it can't happen. Vanishingly unlikely to have happened in both parents. I guess it always seems unlikely when it occurs unless someone once had a cousin with the same thing; being from different countries only really matters if a disease only ever crops up in a very restricted population, and I think Northern Europe would often count as the same thing really. Unfortunately your dds being healthy doesn't alter anything as you'd expect that if you were both carriers then 1 in 4 of your children would be affected. If I could think of any shred of hope from the genetics I would say so, believe me. I think it's all just down to how very, very rare it is, hoping and praying :(

MB is totally right -the vast majority of cases are due to both parents being carriers, but spontaneous mutations can and do occur..some genes are more prone to mutation than others so are likely to occur sporadically as well as familiarly, but two spontaneous mutations would be very very rare indeed.

Also very rare would be a scenario where the baby inherits both copies of a chromosome from the same parent (and none from the other parent)- if that parent has a mutation on that chromosome then the baby would have 2 mutations and be affected by the condition.

A straightforward single gene autosomal recessive syndrome with both parents as carriers gives you a 75% chance of a normal baby (including carriers) and a 25% chance of an affected baby (I'm phrasing it in a general way as the gene for Jeune is not known as yet).

Tamum is more of a 'gene' person than me - I'm chromosomes, she may be able to shed more light on this for you.

Sorry, I took so long to post that Tamum beat me to it.

No, she said exactly the same :)

Thank you all.

Is Jeune's X-linked

At least we're consistent, even if we can't offer any help, emkana. I so wish this waiting was over for you.

(Bluebear, sorry to hijack, but Philly has a thread on SN about Williams- it would be good if you could take a look. Ta)

No expat, it's autosomal.

No, Jeunes shows autosomal inheritance - the autosomes are the chromsomes that arent' X and Y.