What is a recessive condition?

It is estimated that each of us carries at least 5 recessive diseases.

Within each ethnic group, there are certain recessive conditions that are known to be more common.  Within Ashkenazi Jews, there are 19 conditions that are considered common.  Within Sephardic and Mizrahi Jews, there are 17.


A quick genetics 101 lesson:

As a general rule, we get two copies of every gene: one from our mom and one from our dad.  A person can inherit different versions of the same gene, called “alleles.”  Some alleles are dominant, meaning you only have to inherit one copy of that allele from one parent in order to express the condition.  A recessive trait is one where you have to inherit two copies of the recessive allele (the recessive version of that gene) in order to have the condition.

As a simplified example, let’s use eye color.  The recessive trait is blue eyes.  Two parents can have brown eyes and have a child with blue eyes.  How does this happen?  Each parent has one brown allele and one blue allele.  Brown is dominant, so just having one version of that allele means that the person will have brown eyes.  When they have a child, they each pass on only one copy of that gene: either the brown allele version or the blue allele version.  It is random which version is passed on from each parent.  The child could inherit any of the following:

–  Mom’s brown allele + Dad’s brown allele = child with brown eyes

–  Mom’s blue allele + Dad’s brown allele = child with brown eyes who is a silent “carrier” for blue eyes

–  Mom’s blue allele + Dad’s brown allele = child with brown eyes who is a silent “carrier” for blue eyes

–  Mom’s blue allele + Dad’s blue allele = child will have blue eyes

(**Disclaimer: eye color inheritance is actually more complicated than stated above and involves multiple genes, but it is simplified for the sake of this example)

It would be the same for the recessive disease.  If two people are carriers for Tay-Sachs disease, they are not affected and do not have any problems as a result of being “silent” carriers.  However, they could potentially have a child together who actually has the condition Tay-Sachs disease, which is a severe progressive neurodegenerative condition that often causes death in early childhood.  Similar to the example above, because Tay-Sachs disease is caused by the recessive allele, two carriers have a 1 in 4 (25%) chance of having a child who is affected with Tay-Sachs disease.

Why are these conditions common in Jews?

Historically, members of individual ethnic groups such as Ashkenazi Jews have tended to have children with other members of the same ethnic group.  Because of this, over time, the same recessive conditions have stayed common within those populations.

It is important to understand that this has nothing to do with religion.  These are ethnic groups, and it is not just Jews that have common recessive conditions.  All ethnic groups have certain conditions that are more common within its members.   There are also some genetic conditions, such as Cystic Fibrosis, Spinal Muscular Atrophy, and Fragile X that are quite common in all ethnicities and for which testing should be considered in anyone planning to have children.

Once one person identifies which recessive conditions they carry, their partner should make sure they have been tested for the same recessive condition, whether they are a member of the same ethnic group or not.  Anyone can be a carrier of any recessive condition, whether it tends to be one of the common ones in their own ethnic group or not.

How do I know if I am a carrier of a recessive disease?

Usually, you don’t.  The only way to know for sure is to be tested or to have a child with a recessive disorder.  Typically, you would have absolutely no family history of the condition, and you may even already have healthy children.  When two people who are both carriers of the same recessive disease have a child together, there is a 1 in 4 (25%) chance of that child being affected with the disease.  Carriers are not affected with the disease and never will be, but they will always be carriers.  They typically show absolutely no sign that they are a carrier, it will only be known if they have a DNA test for that particular disease.  The first step in preventing having a child with a recessive disease is KNOWING if you and your partner are both carriers.

When should I get tested?

This information is relevant for people who are planning on starting a family.  But the best time to find out if you and your partner are carriers for the same disease is before you and your partner are pregnant, so the sooner the better!  In fact, testing before marriage is ideal.  Being prepared with your options if you find that you are both carriers for the same condition will help you in discussing your plans together without the pressure of an already established pregnancy.

What happens if I find out that I am a carrier for one of these diseases?

First it is important to understand that we are ALL carriers for genetic diseases.  In fact, we are all carriers for several genetic diseases; we just can’t yet do a genetic test for every single condition to know what we all carry.  Currently, we can test for what is most common in our ethnic group.  If you are a carrier for one of these common conditions, now you have some important information.

The next step is to find out which recessive conditions your partner carries.  If you are both carriers for different recessive conditions, there is no risk of your children being affected with those disorders.  However, if you learn you are both carriers for the same condition, you have now taken the first step in preventing your future children being affected with a terrible disease.

What can we do if we are carriers of the same disease?

Finding out that you and your partner are both carriers for the same recessive disease means that you can now explore the options for how to save your future children from this condition.

Options include:

–  Prevention options:

  • Preimplantation Genetic Diagnosis (PGD), a method that uses in vitro fertilization to ensure that the baby will not have the disease. (Using the couple’s egg and sperm, only embryos that have not inherited the disease are implanted.)
  • Use of donor egg or sperm from a non-carrier donor
  • Adoption

–  Diagnosis during pregnancy:

  • Prenatal testing using chorionic villus sampling (CVS) between 10-14 weeks or amniocentesis from 15 weeks
  • Information can be used to make decisions regarding:
    • Preparation for an affected child (more frequent monitoring during pregnancy, any relevant surgical or treatment plans for after birth)
    • Termination

My partner isn’t Jewish, only I am.  Do I still need to get tested?

Yes! Anybody can be a carrier of these diseases.  These specific conditions discussed here are common in Jews, but non-Jews may also be carriers.  In fact, some of these conditions are common in other ethnicities as well. For example, Cystic Fibrosis is common in all ethnic groups, and most common in Caucasians.  If you are a carrier, your partner should be screened to see if he/she is a carrier for the same condition, whether Jewish or not.  If your partner is of different ethnicity, tgtn-dad-babyhere may be other diseases common for their background that they should be screened for and, if they are positive, you should consider being screened for that particular condition as well.  Check with a healthcare provider to learn which other conditions your partner should be screened for based on their background.

I’ve heard people talk about BRCA testing for Ashkenazi Jews. What is this testing, and why isn’t it done with the other conditions on this site?

BRCA testing is very different than carrier testing for recessive diseases for the purposes of planning to start a family.  BRCA1 and BRCA2 are two genes on which changes (or mutations) can cause high risk for certain cancers, especially breast and ovarian cancer.  The high risk for these cancers is conferred by just having inherited one copy of a changed BRCA1 or BRCA2 gene.  In other words, the risk is passed on in a dominant fashion—you only have to inherit one copy of a changed BRCA gene from one parent in order to inherit the higher cancer risks.  Therefore, a person with a BRCA mutation typically has a family history of breast and/or ovarian cancer.  There may also be family history of pancreatic, prostate, melanoma, and other cancers.  The carrier frequency for specific mutations on the BRCA genes in Ashkenazi Jews is about 1 in 40 (2.5%).

If you are concerned about your risk of carrying a BRCA mutation based on a personal or family history of cancer, it is best to meet with a genetic counselor (find one here) to discuss the family history and likelihood of a mutation.  If the family history is suggestive of a possible BRCA mutation, testing can then be pursued. If a BRCA mutation is found, steps can be taken to reduce cancer risks and/or screen for the cancers for which you may be at higher risk.

Babies and children are not typically tested for BRCA mutations because there are no childhood cancer risks associated with BRCA mutations; the cancer risks are elevated in adulthood.  Therefore, BRCA testing is usually not performed until a person is an adult and can provide informed consent for testing.

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