Genetics Northern California

Genetic Carrier Screening

The Prenatal Genetic Carrier Screening Program at Kaiser Permanente Northern California offers optional carrier screening to all pregnant women. Carrier screening checks for silent genetic changes (mutations) that could cause a genetic disease in your baby. You can be a carrier for diseases that have never happened before in your family.

Which genetic diseases are included in carrier screening?
What causes genetic diseases?
How are these disease inherited?
What does it mean to be a carrier?
How do I find out if I am a carrier?
Should I have carrier screening?
What does a negative result mean?
What does a positive result mean?
What if my pregnancy is at risk for a genetic disease?
Will newborn screening test for these genetic diseases?
Can I have testing if I'm not pregnant?

Which genetic diseases are included in carrier screening?
The diseases included in our carrier screening program are:

  • Cystic fibrosis (CF)
  • Spinal muscular atrophy (SMA)
  • Hemoglobinopathies (inherited anemias)
     - Thalassemia diseases
     - Hemoglobin E
     - Sickle cell disease

Additional screening is offered when both parents have Ashkenazi Jewish ancestry

Ashkenazi Jewish Carrier Screening Panel
• ABCC8-related hyperinsulinism
• Bloom syndrome
• Canavan disease
• Familial dysautonomia
• Fanconi anemia, group C
• Gaucher disease
• Glycogen storage disease 1A
• Joubert syndrome, type 2
• Lipoamide dehydrogenase deficiency
• Maple syrup urine disease, type 1B
• Mucolipidosis, type IV
• NEB-related nemaline myopathy
• Niemann-Pick disease, type A
• Tay-Sachs disease
• Usher syndrome, type 1F and type 3

What causes genetic diseases?
Genes are the inherited instructions that determine many traits of a developing baby, like eye color, height, and blood type. Genes that do not work right can sometimes cause genetic diseases.

How are these disease inherited?
The diseases included in this screening program are inherited as autosomal recessive diseases. The genes that cause these diseases come in pairs; you inherit one copy of the gene from each parent. Recessive diseases happen when both copies of a gene are not working right. A baby is at-risk for a recessive disease when both parents are carriers for the same condition. When both parents are carriers, there is a 1 in 4 (or 25%) chance that a baby will have the disease. There is also a 3 out of 4 (or 75%) chance that a baby will not have the disease.
If only one parent passes on a non-working gene to a baby, the baby will not have a disease, but will be a carrier just like the parent..

What does it mean to be a carrier?
A person with one non-working gene for any of these diseases is called a carrier. A carrier also has a working copy of that same gene. Being a carrier does not affect your health, but a pregnancy could be at risk for a genetic disease if the other parent is also a carrier.

How do I find out if I am a carrier?
You can find out if you are a carrier by taking a blood test that checks for these diseases. During one of your first prenatal visits you will fill out a genetic carrier testing form. Your answers determine which tests are ordered. Your doctor or nurse practitioner will order the carrier tests you select. Testing can be done at any Kaiser Permanente laboratory. Results usually take about two weeks.    

Should I have carrier screening?
Carrier screening can give you information about genetic risks that are not usually found by other testing. Most of the time, there is nothing in your family's medical history to tell you if your baby could be at risk for a recessive disease. Some conditions may be diagnosed soon after birth by the California Newborn Screening Program. However, if you want to know about your genetic risks during pregnancy, you may want to have carrier screening.
Some diseases are more common in certain ethnic groups. You can identify some of your risks by considering where your ancestors lived before they came to the United States.
  • If you have any Southeast Asian ancestry, consider testing for hemoglobinopathies (inherited anemias), including hemoglobin E.
  • If either you or your partner has any African (Black) ancestry, consider testing for hemoglobinopathies (inherited anemias), including sickle cell disease.
  • If you and your partner both have any Ashkenazi Jewish (Eastern European) ancestry, consider testing for diseases more common in the Jewish population. These include Tay-Sachs disease, Canavan disease, familial dysautonomia, Gaucher disease and 12 other diseases.

What does a negative result mean?
A negative result means that you are unlikely to be a carrier for any of the diseases you were screened for. No further testing is generally needed. These tests are very accurate, but they will not identify all carriers.

Carrier risks after a negative result: CF and SMA

CYSTIC FIBROSIS

Carrier risk

Carrier detection rate

Carrier risk after a negative result

African American (Black)

1 in 61

78%

1 in 275

Ashkenazi Jewish

1 in 24

96%

1 in 575

Asian American

1 in 94

55%

1 in 210

Caucasian (White)

1 in 25

92%

1 in 300

Hispanic

1 in 58

80%

1 in 285

 

SPINAL MUSCULAR ATROPHY

Carrier risk

Carrier detection rate

Carrier risk after a negative result

African American (Black)

1 in 72

90%

1 in 375

Ashkenazi Jewish

1 in 67

93%

1 in 918

Asian American

1 in 59

93%

1 in 907

Caucasian (White)

1 in 47

95%

1 in 921

Hispanic

1 in 68

93%

1 in 906

 

What does a positive result mean?
A positive result means that you are a carrier for that particular disease. Follow-up testing will be offered to the other parent to find out if the pregnancy is at risk. When both parents are carriers for the same disease, their baby is at risk for the disease.


What if my pregnancy is at risk for a genetic disease?
When a pregnancy is at risk for one of these conditions, prenatal testing can find out before birth if the baby has the disease. There is a 75% chance the results will show the baby does not have the condition. However, there is also a 1 in 4 (25%) chance to find out that the developing baby has the condition. People who learn that their baby has one of these diseases may use the information to help with delivery planning and specialized newborn care, while others may consider whether to end the pregnancy. Your genetic counselor will discuss your options in detail and provide ongoing support. If you choose not to test the baby during pregnancy, testing can be done soon after birth.

Will newborn screening test for these genetic diseases?
Newborn screening in California tests for cystic fibrosis, sickle cell disease, and some thalassemia diseases, along with certain metabolic and endocrine disorders. Spinal muscular atrophy will be added to the California Newborn Screening Program in 2020. Most of the conditions in the Jewish carrier screening test are not included as part of newborn screening.

Can I have testing if I'm not pregnant?
If you are planning a pregnancy, you may want to consider genetic carrier testing before you are pregnant. This is also called preconception carrier screening (i.e., screening before the pregnancy begins). Preconception screening has the advantage of giving more reproductive options if a couple is at risk for one of these conditions. Preconception carrier screening can be arranged by talking with your gynecologist or primary care provider.


Reviewed by: Catherine Klumpp,LCGC; Kimberly Barr,LCGC; Kimberly Wendt,LCGC
Last reviewed: August 20, 2019