What are the Probabilities of Having a Child with Thalassemia?

We are often asked what are the odds of having a thal minor or major child. I have often seen the odds mis-stated and just today saw a post elsewhere that stated that two minors have a 50% chance of having a major. This is not correct. There are no circumstances where there is a 50% chance of producing a major, other tham a major and minor having a child together.

It is actually very simple and you can check it yourself with two coins of two different denominations. Have a penny represent each parent's non-thal gene and a dime to represent the thal gene from each parent. Check how many different combinations there are. There are only four possibilities. One penny from each parent = no thal genes (non thal). One dime from each parent = two thal genes (major). A dime from the mom and a penny from the dad = one thal gene (minor). A penny from the mom and a dime from the dad = one thal gene (minor). As you see, 1/4 (25%) will be either non thal or major, but 1/2 (50%) will be minor. A major parent and a minor parent will produce a major 50% of the time (as was with Lisa), and a minor 50% of the time. A major parent with a non thal parent will produce minors 100% of the time.

For a diagram of what two minors will produce, see the attached diagram from
http://sickle.bwh.harvard.edu/thal_inheritance.html

I think I have read this post before!?!?! But it was marked new! Deja vu or something

How do we know if the parents are carriers?  Is genetic testing the only test available?

A hemoglobin electrophoresis can determine if the parents are carriers. Trait carriers normally have elevated fetal hemoglobin levels.

From http://findarticles.com/p/articles/mi_g2601/is_0006/ai_2601000646

Hgb F:

    * 2-5% (β-thalassemia minor)
    * 10-90% (β-thalassemia major)

A hemoglobin electrophoresis can determine if the parents are carriers. Trait carriers normally have elevated fetal hemoglobin levels.

From http://findarticles.com/p/articles/mi_g2601/is_0006/ai_2601000646

So, both my parents has to undergo that test as well?

Now Andy, my question is specifically for me...would I need to find out which hemoglobin subunit is missing in my partner's? Meaning, do we have to determine which thal he is a carrier for --alpha or beta? If he is alpha-thal carrier and I am beta-thal minor and we have a child with thal, is there a chance of the child expressing major traits? If so, what is the probability for each pregnancy having thal major and so on?
Deidre

Hi Deidre,

Yes, you do need to find out if your partner is beta thal minor. If he is, there is a 25% statistical chance of having a major. However, odds mean nothing when you fall into that 25% category, so testing is essential.

If your partner carries the alpha gene, the result can vary greatly. If he has two alpha genes there is a possibility of having a child with characteristics of thal intermedia if the child inherits one beta and two alpha  genes. However, someone having that combination can also exhibit minor symptoms only, but at the most, symptoms will be intermedia-like and never major. If he has only one alpha gene there is no chance of having a child with an intermedia condition.

Your partner should definitely be tested before you decide to conceive.

well both of my parents are thal minors with 4 children so how is it possible for my brother (may he rest in peace) and i to have thal major?

The odds are only mathematical chances. When both parents are minor, the children can carry no thal genes, one thal gene (minor) or two thal genes (major or intermedia). I've known several families with 3 majors. Keep in mind what I said in the previous post. Odds mean nothing when you fall into that 25% category, as you and you dear brother both did. My condolences on your loss.

The statistical odd of having a Thal major child is 25% if both parents are minor. However, Human genetic disorder is complicated enough to beat those odds. I have seen a thal major child with one parent is Thal minor and the other is just fine. One would question it but its true and DNA proved the paternal test.

Regards.

Yes this is true, but i think in that case there was another muted gene (could be one of the regulartery genes) that togather with the thal trait produce or lead to a thal major instead of a minor.

i also read an article ( which i will try to find) saying that there are certain thal mutations that are dominant and manifest themselves though the other gene is normal.

I totally agree that it is very complicated
Manal

miltswifey,
it is a one in 4 chance in each pregnancy.  so each time your mum got pregnant she had a 25% chance of having a thal major child.  It is not a 25% chance in all her pregnancies put together.
When my eldest child was diagnosed i was 5 months pregant with my second.  i remember saying to the doctor well at least this child i'm carrying will be fine.  thats when he made it clear that the child i was carrying had the same chances as my first pregnancy.  it was a long 5 months before we found out whether our second born would have it but he was born with thal minor trait.  thank god.

vic

canadian family,
i knew i had thal minor and my husband was tested before we decided to have children.  he was told he had nothing.  so we had christian.  they were wrong, my husband has another trait that when combined with my thal minor creates sicklecell thal.  so not all tests find what they should be looking for.
vic

Exactly, We human think we know a lot but infact its just a surface we are scratching.

Regards

I have thal minor.  My ex husband, I do not know about, and he will not cooperate.  I was told my son was clear when he was young.  Now he is 27 and I feel he shows symptoms similar to mine and want him re-tested.  He will not take it seriously.  What are the statistics I should tell him, if any?
Also, I am adopted.  I connected with my birth Mom when I was 40, and we are close, but she refuses to discuss my thalassemia as real.  Even when her Mom was in the hospital, dying, one of the contributing causes, uncontrollable anemia.  Is there anything I should ask her, or any issue I should force?  My bio father is 100% Swedish, Mother, 50% Cherokee, 50% a mix that includes some type of French/Canadian/Native American, Irish, and
I let these matters slide before because I was clueless people really knew anything about thalassemia nowadays.  Well, thanks to thalpal, that has changed, and I can no longer ignore this important matter.  I have been to so many doctors I feel I am an expert on doctors.  Now, I see my thalassemia medical expert isn't even a doctor, it's ANDY!!!!  Andy, THANK YOU AGAIN, so much, for your dedication to increasing the quality of thal's lives through your knowledge.