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Ethnic Based

Ethnic Based Genetic Screening: Know Your Risks & Your Options

Preconception screening and genetic counseling is offered to women or couples at increased risk for passing certain genetic disorders onto their children. Care begins with a personalized risk assessment followed by counseling and screening for those genetic diseases appropriate to the patient's ethnic background (where their ancestors are from). If test results indicate that either partner carry a hereditary disease, education and support needed to make informed reproductive decisions are provided.

Services includes:

  • Personalized risk assessment
  • Carrier screening
  • Discussion of reproductive options for carrier couples

What are Ethnic Based Genetic Diseases?

A lot of people don't know what genetic diseases are or that they can affect people of certain ancestry at higher rates than other members of the population. All people are likely to be carriers of several autosomal recessive genetic conditions, but it is not always clear as to which conditions are most likely to be carried by your family. Autosomal recessive conditions are diseases that require both parents of a baby to be carriers of the same genetic condition in order to have an affected child. A carrier is a healthy person who has one normal copy of a gene and one copy of the gene that does not work properly. If both members of a couple are found to be carriers, they are at 25 percent risk of passing a given genetic disease on to their baby with each pregnancy. Carriers for these conditions are healthy people, so they are often surprised by the birth of a child with a recessive condition. A simple blood test is all that it takes to find out if you are a carrier prior to pregnancy. This allows for reproductive planning and the ability to have a healthy child.

Genetic counseling and carrier screening are available to allow couples to make informed reproductive decisions. Advanced technologies make having a healthy baby possible for carrier couples. For couples found to be at increased risk, reproductive counseling, prenatal diagnosis and treatment will be coordinated. Our team can provide genetic counseling, screening and treatment to anyone who suspects their family heritage may place them in a high-risk category.

If one member of couple is known to be a carrier, the other member of the couple may need to seek genetic counseling in order to make sure that the most sensitive test is used to assess carrier status, as not all carrier methods can detect genetic changes in people of all backgrounds.

Below is a chart of diseases frequently carried by people of specific ethnic backgrounds. More information about each condition can be found below

Ethnicity Disease Likelihood

African-American

Sickle Cell
Alpha-Thalassemia
Cystic Fibrosis
SMA
Beta-Thalassemia

1 in 10-12
1 in 30
1 in 61
1 in 72
1 in 75

Ashkenazi Jewish

Gaucher disease
Cystic Fibrosis
Tay-Sachs disease
Fam. dysautonomia
Canavan disease
SMA
And more

1 in 15
1 in 25
1 in 25
1 in 40
1 in 40-52
1 in 67

Asian

Alpha-Thalassemia
Beta-Thalassemia
SMA
Cystic fibrosis

1 in 20
1 in 50
1 in 52-59
1 in 94

European

Cystic Fibrosis
SMA

1 in 25
1 in 47

French Canadian, Cajun

Tay-Sachs disease
Cystic Fibrosis

1 in 25
1 in 25

Hispanic

Cystic Fibrosis
Beta-Thalassemia
SMA

1 in 40-60
1 in 30-50
1 in 68

Mediterranean

Beta-Thalassemia
Cystic Fibrosis
Alpha-Thalassemia
Sickle Cell

1 in 20-30
1 in 29
1 in 30-50
1 in 40

Many people are of mixed ethnic background or do not know where their ancestors are originally from. For these people, screening for cystic fibrosis is recommended for all, screening for anemia may be indicated to determine risk for sickle cell anemia and thalassemias, and pan-ethnic expanded carrier screening is available. Expanded screening is a blood test that includes screening for a large number of serious recessive conditions. The screening method (genotyping) looks for specific genetic changes seen in people of certain ethnic backgrounds at a high frequency, but may miss rarer genetic changes in these genes. As technology becomes more advanced, thorough screening (sequencing) for many conditions at once may be accessible due to lower costs.

 

Disease Details

 

Alpha thalassemia

Alpha thalassemia is a blood condition that can result in fatigue, pallor, weakness and serious complications. People with this condition have low levels of hemoglobin which is needed to carry oxygen in the blood. The body tries to produce more blood cells to make up for the lack of hemoglobin and this can result in abnormal shape of some bones where blood is made. Some people need transfusions of blood which can result in complications like heart disease or infections in rare cases. It is most common in people with ancestors from Southeast Asia, Mediterranean countries, North Africa, the Middle East, India, and Central Asia

The genetics of alpha thalassemia is complex, as we have two copies of the alpha globin genes, HLA1 and HLA2. If missing 4 copies, the fetus often presents with full body swelling during the pregnancy and often will not survive. If missing three copies of the gene, the child will present with alpha thalassemia in childhood.

Screening for this condition is by a blood test called hemoglobin electrophoresis. If you or your partner has an abnormal screen, your physician will discuss next steps for determining whether your offspring may be at risk for this condition.

 

Beta-thalassemia

Beta thalassemia is a blood condition that can result in fatigue, pallor, weakness and serious complications. It is similar to alpha thalassemia in many ways. People with this condition have low levels of hemoglobin which is needed to carry oxygen in the blood. The body tries to produce more blood cells to make up for the lack of hemoglobin and this can result in abnormal shape of some bones where blood is made. Some people need transfusions of blood which can result in complications like heart disease or infections in rare cases. It is most common in people with ancestors from Mediterranean countries, North Africa, the Middle East, India, Central Asia, and Southeast Asia.

Beta thalassemia can present at birth (thalassemia major) or later in childhood (thalassemia intermedia), depending on the level of hemoglobin loss of function.

Screening for this condition is by a blood test called hemoglobin electrophoresis. If you or your partner has an abnormal screen, your physician will discuss next steps for determining whether your offspring may be at risk for this condition.

 

Cystic fibrosis

Cystic fibrosis (CF) is a disease that most severely affects the lungs and pancreas. Due to an abnormality in salt transport in people with CF, abnormally thick mucus is produced in the lungs causing difficulty breathing and increasing the frequency of serious lung infections. The pancreas is unable to produce important enzymes necessary for the proper absorption and processing of fats. This often results in decreased life expectancy. CF is a disease seen with equal frequency in the general Caucasian population and Ashkenazi Jewish population; approximately one in 25 Caucasians carries a defective gene for the disease. This condition can also be carried by people of all other backgrounds, but at a lower frequency. Carriers are detected by a blood DNA test. Most blood tests for CF are aimed at detecting the genetic changes common in the Caucasian population. People of other background may need a more detailed DNA test called sequencing than can look for genetic changes throughout the entire gene.

 

Familial Dysautonomia

Familial dysautonomia (FD), also known as Riley-Day Syndrome, is a disease that causes the autonomic and sensory nervous systems to malfunction. The autonomic nervous system controls bodily functions such as swallowing and digestion, regulation of blood pressure and body temperature and the body’s response to stress. The sensory nervous system helps the body to taste, recognize hot and cold and identify painful sensations. The disease is also known as HSAN III (hereditary sensory and autonomic neuropathy, type III).

The hallmark of FD is the lack of overflow tears with emotional crying. Children with FD may have difficulty feeding. They also may be unable to feel pain, and can break bones or burn themselves without realizing they've been injured.

The disease is caused by mutations in the IKBKAP gene. An estimated one in 30 Ashkenazi Jews carries the FD gene change, found on chromosome 9. Carriers don’t display any symptoms or warning signs of FD.

Currently, there is no cure for FD. The lifespan of those affected with FD is often shortened. Treatments aim at controlling symptoms and avoiding complications. Treatment strategies can include using special feeding techniques and special therapies, medications, artificial tears, respiratory care and orthopedic management.

 

Gaucher Disease

There are three different types of Gaucher (pronounced go-shay) disease (type I, II, III). Type I is the most common form of the disease; an estimated one in 14 Ashkenazi Jews is a carrier. The gene is located on chromosome 1. The signs and symptoms of Gaucher disease vary greatly and can appear at any age. The most common symptom of type I Gaucher disease is painless enlargement of the spleen and/or liver with absence of central nervous system involvement. Other symptoms may include bruising, bone pain, frequent nosebleeds, and a lack of energy. Also, children with type I Gaucher disease are often shorter than their peers and may have delayed puberty.

People with Gaucher disease lack an enzyme called glucocerebrosidase and are unable to break down a fatty substance in their cells. This fatty substance builds up in the liver, spleen, bone marrow and other areas of the body. This build-up leads to the medical complications of Gaucher disease.

Although there is no cure for Gaucher disease, there are some treatments available for managing and relieving the symptoms. Enzyme replacement therapy is an effective form of treatment, but is quite expensive and time-consuming. The treatment consists of a modified form of the glucocerebrosidase enzyme given intravenously. A newer therapy oral therapy, miglustat, is available for those patients who are not suitable candidates for enzyme therapy. These therapies can lead to improved quality of life for affected individuals and their families.

 

Tay-Sachs

Tay-Sachs disease is an inherited, genetic disorder that causes progressive degeneration and destruction of the central nervous system in affected individuals. Babies born with Tay-Sachs disease appear normal at birth, and symptoms of the disease do not appear until the infants are approximately four-to-six months of age. It is at this time that these children begin to lose previously attained skills, such as sitting up or rolling over. They gradually lose their sight, hearing and swallowing abilities. There is severe developmental delay. These children usually die by the age of four.

Individuals with Tay-Sachs disease lack a substance in their body called hexosaminidase A (Hex A). Hex A is responsible for breaking down a certain type of fat called GM2-ganglioside. When Hex A is missing from the body, it cannot break down this fat. The fatty substance accumulates to toxic levels in the body, mainly in the brain and nervous system. There is no cure for Tay-Sachs, although research is on-going regarding possible treatment options.

An estimated one in every 25 Ashkenazi Jews and French Canadians is a carrier for Tay-Sachs disease. TSD is also carried at a high rate in people of Cajun and Irish descent.

Screening for Tay-Sachs is somewhat complex. The gold standard includes enzyme analysis which must be performed on blood as well as DNA screening. DNA panels often only look for those genetic changes seen in the Jewish population. Those of other ethnic backgrounds should have sequencing of the gene for Tay-Sachs if enzyme testing is abnormal.

 

Sickle cell anemia

One out of 10-12 people of African descent are carriers for sickle cell anemia (SCA). SCA is a condition that causes the blood cells to be in a sickle shape instead of their usual shape and have more difficulty moving through small vessels in the body to carry oxygen. People with SCA can have a “crisis” in which they experience significant pain in the bones and may need IV fluids and transfusions of blood. Certain medications can decrease the risk for these crises. Carriers of this condition may say they have “sickle cell trait”. Carriers generally are well, but can occasionally have complications at high altitudes. Carriers can be detected using a blood test called hemoglobin electrophoresis in most cases. DNA testing can also be performed to identify the specific genetic change for reproductive purposes.

 

Spinal Muscular Atrophy (SMA)

Refers to a group of diseases which affect the motor neurons of the spinal cord and brain stem, which are responsible for supplying electrical and chemical signals to muscle cells. Without proper signals, muscle cells do not function properly and thus become much smaller (atrophy). This leads to muscle weakness. Individuals affected with SMA have progressive muscle degeneration and weakness, eventually leading to death.
There are several forms of SMA, depending on the age of onset and the severity of the disease. Two genes, SMN1 and SMN2, have been linked to SMA types I, II, III and IV. Type I is the most severe form of SMA and is characterized by muscle weakness present from birth, often manifested by difficulties with breathing and swallowing, and death usually by age 2-3 years. Type II has onset of muscle weakness after 6 months of age, and can obtain some early physical milestones like sitting without support. Type III is a milder form of SMA, with onset of symptoms after 10 months of age. Individuals with Type III SMA often achieve the ability to walk, but may have frequent falls and difficulty with stairs. The weakness is more in the extremities, and affects the legs more than the arms. Type IV is the mildest form and is characterized by adult onset of muscle weakness.

SMA is most often caused by a deletion of a segment of DNA, called Exon 7 and Exon 8, in the SMN1 gene located on chromosome 5. Rarely, SMA is caused by a point mutation in the SMN1 gene. Carrier testing for SMA measures the number of copies of the deleted segment in the SMN1 gene. A non-carrier is expected to have 2 copies present (no deletion), while a carrier will have only 1 copy present (a deletion of one copy). However, carrier testing will not identify carriers of point mutations.

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