Does a child having an autosomal dominant trait mean a parent has to have it?

Your daughter's condition probably doesn't work like the stuff we learned in high school--you know, the "In pea plants tall (T) is dominant to short (t) blahblahblah..." That's a very simplified view stripped down so students can get the basic idea and it doesn't cover all the possible workings of alleles and genetics.

Autosomal alleles can vary in penetrance. That means even if a person inherits the allele(s) they may not have the condition. Yeah, it goes against what you learned but like I said, the pea-plant and punnet square problems are necessarily simplified so you can get the basic idea.

It's also important to note the alleles and genetics you're reading about are not only about bicuspid valves vs. non-bicuspid valves like the tall vs. short pea plants. There's no allele for the specific formation of the heart valve, what they're talking about is the genetic instructions on how all connective tissue form in your body. If the tissue forms a certain way it may affect that part of your body in that way, or it might not. Think of it like dumping sand in your car's gas tank. The most likely result would be in the fuel injectors but the sand could also cause a different problem in another part of the car, or in several systems. (I'll admit here I know little about cars so I hope the general idea is clear.)

Most genetics isn't an on-off thing anyhow, like eye color--we don't have only blue eyes or brown. There are multiple alleles interacting and they don't only affect the color in your eyes. There are some genetically inherited conditions that are straightforward and basically determined by one allele but that's not true of all inherited conditions.

Just from googling around it looks like the genetic basis for bicuspid aortic valve is still not nailed down. I think a section of one paper makes this clear:

"Although previous studies have suggested an autosomal dominant inheritance pattern of BAV (10,15,24), genetic heterogeneity has been a common finding in genetic studies of CV disease in the young (25). Therefore, it is likely that mutations in diverse genes with dissimilar inheritance patterns are responsible for the development of BAV in different families."

Genetics is still a pretty new science and it's easier to say "this disease seems to be inherited in some people" than "this single allele right here causes the disease in all cases." It takes years and years to study genetic diseases, it often involves multiple generations. In people that makes scientific studies very, very slow.

As for the second part of your question there's several answers--one is mostly covered above, it's not 1 allele involved. Autosomal dominant alleles may simply be rare, may cause more severe defects in some cases (which would mean they aren't passed on) or whatever.

I *highly* suggest you talk to a Geneticist about this, he/she can give you the most current information and recommendations for your family. I don't want to scare you but if it's genetic you or another family member may have a silent or less-expressed form of the disorder. There also may be studies on the genetic inheritance. Those could provide valuable information for your grandchildren.

Yes. It means , in this case, that since it is autosomal dominant that an abnormal gene from ONE parent can cause the disease (condition), even though the matching gene from the other parent is normal. The abnormal gene dominates (usually) if passed on.

There are two autosomes present, yet most of the time the faulty gene copy will dominate the normal one from the other parent.

It is possible that enough of the good gene expression allows for proper , normal, growth of the valve (in this case) -- but typically if an autosomal dominant trait is passed by one parent it creates the issue.

Both of you could have it -- but due to rarity and assuming neither of you have this valve deformation -- there is only 1 fault gene/trait potentially being passed on.

With genetics , with just one of you having this trait -- there is a 2 in 4,.. 50% chance with each pregnancy of having a child with the same mutation as the parent with a heterozygote, disease causing mutation on one of your chromosomes but a normal copy of the gene on the other chromosome.

Heterozygote is one normal one mutation for one parent.

Homozygote = one parent having 2 disease causing mutation and no normal copies of the gene (for reference).

See this explanation -- and visual for reference:

http://www.medstudentlearning.com/node/1810

The probability in the general population of ~1% is somewhat complex genetics -- But I can refer you to the Hardy-Weinberg Equilibrium, and X² -tests. This H-W formula and genetic tables, confidence intervals and weighted significance break down into the about 1% prevalence of bicuspid aortic valve (~0.9% to 1.36%).

Take care,

The thing about the dominant trait is that it represents only 50% of the gametes an infected parent has,meaning one out of every two sperm are faulty if the father has the trait. When fertilisation occurs there is a 50% chance that the trait will be passed on so that means if the parents have 4 children only 2 will be infected with the faulty gene. So to answer your question,yes one parent must have the trait for it to be passed on but that doesn't guarantee that it will be passed on and furthermore i don't think that its a very common genetic defect so it only affects a small percentage of the total population.