Carrier Screening

Maybe you’ve seen some recent news articles about children with genetic diseases. Or maybe someone in your family has a child with a genetic condition. Diseases like Tay Sachs, Cystic Fibrosis or Sickle Cell Disease might ring a bell. And you might be wondering what the chances are that you could have a child with a genetic disease.

The purpose of this post is to provide you with information about what it means to be a “carrier” of a genetic condition, what your options are for testing, and what you can do about it if you discover you are a carrier of a genetic disease.

We have two copies of every gene. One copy comes from your mother, the other from your father. Genes are the instructions for the body – they tell our bodies everything from how big our feet should be, to what color our hair should be, to how to digest our food, and everything in between. We all have mutations, or changes, in our genes. It’s what makes us unique from each other. Some mutations have absolutely no effect on our health whatsoever, but, in some cases, a mutation can lead to disease.

If you are a “carrier” of a genetic disease, this means that you have a mutation in one of your two copies of the gene associated with that disease. So, if you are a “carrier” of Tay Sachs Disease, that means that of your two copies of the gene associated with Tay Sachs Disease, one copy has a mutation. That mutation causes the gene to be dysfunctional, and, as an effect, the body cannot understand the instructions that the gene is trying to provide and can’t perform its duty. But, as a “carrier”, you have a second copy, perfectly functional, and able to provide the body with the necessary instructions. So, for you as a “carrier”, you are healthy, you do not have that disease.

If you have a child with someone who is a carrier of the same disease as you, then you have a risk of having a child with that genetic disease. Why? Because if the child inherits the mutation copy of the gene from BOTH of you, he or she will have no working copies of that gene, neither copy will function to provide instructions for the body, and disease will occur.

Image :http://www.jewishgeneticdisordersuk.org/index.php?/jewish_genetic_disorders/introduction_to_genetics

Above, you see a picture of two parents who are carriers. In each pregnancy that this couple has, there are 4 possible outcomes for their child. In one instance, the child has inherited both working, non-mutation genes from each parent (non-carrier child), in two instances, the child has inherited a mutation copy from one parent, and a non-mutation copy from the other parent (carrier child), and in one instance, the child has inherited both mutation copies of the gene and is “affected”, meaning that s/he has the disease. So, statistically, in a couple who are BOTH carriers of a genetic disease, there is a ¼ (25%) chance IN EACH PREGNANCY, that the child will have the disease. If only one parent is a carrier, there is no risk that the child will have the disease, but children can be carriers, which will be important for them to know when they are older and ready to have their own children.

So, how can you find out if you are a carrier of a genetic disease? There is genetic screening available. There is screening available that is ethnicity-based because certain ethnic groups are more likely to be carriers of certain conditions. For example, if you are Jewish, there is a group of diseases for which you’re most likely to be a carrier. If you don’t know your ethnicity, or if you’re mixed, or if you want extra screening, there are broad “Pan-Ethnic” screening options available.

What if you are found to be a carrier? The first step is to get your partner tested to find out if he or she is a carrier of the same condition. You should also inform your family members that you are a carrier. If you are a carrier of a genetic condition, that mutation is running in your family, so other family members may want this information and can get tested.

What if you and your partner are both found to be carriers?  Well, now you have some decisions to make:

-       You can get prenatal testing as early as the end of the first trimester to learn whether or not the baby will have the disease. You can find this out in order to prepare yourselves for a child who will have special needs, or you may choose to end the pregnancy.

-       You can use In-Vitro Fertilization to create embryos outside the body, do genetic testing on the embryos, and then only implant the ones who do not have the disease. This is an invasive process, and can be expensive.

-       You can use donor eggs or sperm, or choose to adopt.

More questions? Want to get screened? Give me a call, and we can make a plan for your family.  

Chromosomes

Chromosomes. Does the word remind you of high school biology? Punnett squares? Am I making you sweat? Keep reading...I won’t make you take a pop quiz. 

The purpose of this post is to refresh your memory about chromosomes and talk about why they matter now. 

If you are a women over age 35, you may have been told that you better hurry up and have a baby because your eggs are “getting old.” Facebook and Apple recently announced that they would pay for egg freezing for their female employees. Women who are having their babies over age 35 are considered to be of “Advanced Maternal Age,” or AMA. This is all connected to chromosomes. 

Chromosomes are the structures inside cells on which the DNA resides. DNA is the alphabet for genes, the instructions for our body. Humans have 46 chromosomes, and they come in 23 pairs. One of each pair comes from your mother, and the other from your father. These include 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. So, for the women reading this, you have 46 chromosomes, including two X chromosomes: you are 46,XX. Men reading this have 46 chromosomes, including an X and a Y chromosome, which makes you male: you are 46,XY.

Here's a picture of the chromosomes of a female (46,XX). This broad look at the chromosomes all matched up in pairs is called a karyotype: 

Image: www.dnalc.org

Each egg and each sperm has only 23 chromosomes. The combination of a sperm and an egg will result in the expected 46 chromosomes. Women will contribute an X chromosome (because that’s all they have), and men will contribute an X chromosome half the time, and a Y chromosome the other half of the time.  Ever wonder what determines the gender of your baby?  Now you know: It’s determined at conception based on which sperm penetrates the egg. If that sperm has an X chromosome, you’re having a girl.  If it’s a Y, you’re having a boy. 

Women are born with all of their eggs and they age along with her. Men make new sperm constantly. When we talk about women’s eggs “getting older,” we mean that the ability to release a mature egg at ovulation with exactly 23 chromosomes gets more difficult.  Around age 35, it becomes increasingly difficult.  

Most pregnancies conceived with a chromosomal abnormality will result in a miscarriage, usually very early, sometimes even before a woman knows she’s pregnant. As a women ages, her chances of conceiving a pregnancy with a chromosomal abnormality increases, as does her risk for miscarriage. There are some chromosomal conditions, however, that may not miscarry, including Down Syndrome (which is a condition in which there is an extra, third copy of chromosome 21), Trisomy 13 (a third copy of Chromosome 13), and Trisomy 18 (a third copy of Chromosome 18). Babies with Trisomy 13 and Trisomy 18 usually have significant medical problems and are not able to survive more than a few days or months. Individuals with Down Syndrome can often live into their 50s or 60s or longer, but may have learning disabilities and health problems, such as heart defects. 

Here is the karyotype of a male with Down Syndrome (47,XY, +21) . See the extra copy of Chromosome 21? 

Image: http://openi.nlm.nih.gov/detailedresult.php?img=3232533_IPC-4-3-g004&req=

So, what are the chances of having a baby with Down Syndrome, Trisomy 18 or Trisomy 13?

• At age 35, the chance of having a baby with Down Syndrome is about 1/338 (0.3%); by age 40, that chance increases to about 1/84 (1.2%) 
• At age 35, the chance of having a baby with Trisomy 13 is about 1/10,000 (0.01%); by age 40, that chance increases to 1/2700 (0.03%)
• At age 35, the chance of having a baby with Trisomy 18 is about 1/4200 (0.02%); by age 40, that chance increases to 1/1140 (0.09%)

So, as you can see, the chance increases as a woman ages. Trisomy 13 and 18 are much more rare than Down Syndrome, but risk still increases as a woman ages. 

What are the chances of having a pregnancy that has any chromosome abnormality, including those that are likely to miscarry? 

• At age 35, the chance of a pregnancy with any chromosome abnormality is approximately 1/115 (0.9%)
• At age 40, the chance of a pregnancy with any chromosome abnormality is approximately 1/30 (3.5%)*

Each person views these risk numbers differently. Some people may see these numbers and think: “This is a low risk; what’s the big deal?”  Some people may see these numbers as high risk, and want to get more information for themselves, beyond the general statistics for their age group. 

In particular, some people, especially those who have already experienced several miscarriages or have had a child with one of these conditions, may want to know if they have a predisposition towards conceiving a pregnancy with a chromosomal condition. 

So what are the options for screening and testing?

Should everyone get screening?

What can you do with the testing/screening results? 

Stay tuned for future blog posts! 

*Risk numbers from: Gardner & Sutherland. Chromosome Abnormalities in Genetic Counseling, 3rd Edition, 2004. Risk statistics for a pregnancy with any chromosome abnormality are those detected at 10-11 weeks gestation, so may be higher at conception when considering those conceptions that would have miscarried earlier due to the chromosome abnormalities. 

Getting Started

When I tell people what I do for a living, the first question people have is, "What is a genetic counselor?" It's a good question because genetic counseling can take many forms. Some genetic counselors work in hospital settings. Some work in private physician offices, or in fertility clinics. Others work in specialty clinics, like cardiology clinics. Still others work in labs or in research facilities. There are actually only a few thousand board certified genetic counselors practicing in the US. We all have a common goal: we all want to help people. We want to provide accurate and useful information, and support and guide people through a complex and sometimes scary and emotional world. We want people to feel heard and validated, and comforted and cared for.

My husband's job brought us to the Los Angeles area, and I realized a need for an independently practicing genetic counselor. There are many wonderful genetic counselors here in Los Angeles, but the current health care model under which they work only allows for people with a known "risk" or "problem" to be seen. I see a need for education and empowerment for everyone, especially as genetic testing becomes more standard of care and widely used. My goal is to be a resource for everyone - doctors, nurses, midwives, patients, family members - to understand how genes affect our health, and what genetic testing can offer. I have no agenda, other than to provide accurate, un-biased, up-to-date information in an understandable an accessible way. It would be a privilege to work with you and your family.