Genetic Carrier Screening
Knowing whether you and your partner are carriers for a genetic disease can help you plan for a healthy family.
Screening in the prepregnancy period offers the additional advantages of identifying, before pregnancy, couples at risk of having children with genetic diseases and offering appropriate testing to optimize patient education, counseling, and options for achieving pregnancy.
Couples at risk of having children with specific genetic diseases can be referred to a genetic counselor to review risk of disease inheritance and to discuss potential interventions, such as preimplantation genetic testing.
- Carrier screening and counseling ideally should be performed before pregnancy.
- If an individual is found to be a carrier for a specific condition, the individual’s partner should be offered testing in order to receive informed genetic counseling about potential reproductive outcomes.
- If both partners are found to be carriers of a genetic condition, genetic counseling should be offered. Prenatal diagnosis and advanced reproductive technologies to decrease the risk of an affected offspring should be discussed.
- Your newborn should be screened; pre pregnancy screening does not replace newborn screening.
All women who are wanting to conceive should be screened to see if you carry the genes for:
- Cystic Fibrosis
- Spinal Muscular Dystrophy
If there is a family history of :
- Fragile X
- Hemoglobinopathies
If you are of Eastern European or Ashkenazi Jewish Descent you should be additionally screened for:
- Canavan disease
- Familial dysautonomia
- Tay-Sachs disease
Cystic Fibrosis
Cystic fibrosis occurs from a faulty protein that affects the body’s cells, tissues, and the glands that make mucus and sweat.
Mucus is normally slippery and protects the linings of the airways, digestive tract, and other organs and tissues.
People who have cystic fibrosis make thick, sticky mucus that can build up and lead to blockages, damage, or infections in the affected organs.
The most serious and common complications of cystic fibrosis are problems with the lungs, also known as pulmonary or respiratory problems, which may include serious lung infections. Inflammation also causes damage to organs such as the pancreas.
The standard test to check for possible cystic fibrosis carriers looks for 23 of the most common disease-causing gene mutations.
If you have a negative test, there is a 99% chance you are not a carrier. However, if you have a negative test, there is still a small chance that you could carry a CFTR mutation that did not show up on the test, since there are now more than 1700 mutations identified. The incidence is 1 in 2,500 individuals.
If one partner is a carrier for a cystic fibrosis gene mutation, then the next step is to test the partner, if this has not been done. If both parents are cystic fibrosis carriers, then prenatal diagnostic testing may be performed to see whether your unborn baby has cystic fibrosis or is a carrier.
What is the risk if I carry the CTFR gene and my partner carries the CTFR gene?
A person inherits two copies of the CFTR gene, one from each parent.
If each parent has a normal CFTR gene and a mutated CFTR gene, each child has a:
- 25% chance of inheriting two normal genes
- 50% chance of inheriting one normal gene and one gene with a mutation and being a cystic fibrosis carrier
- 25% chance of inheriting two genes with mutations and having cystic fibrosis.
Spinal Muscular Atrophy
Spinal muscular atrophy (SMA) refers to a group of hereditary diseases that can damage and kill specialized nerve cells in the brain and spinal cord (motor neurons). Motor neurons control movement in the arms, legs, face, chest, throat, and tongue, as well as skeletal muscle activity, such as speaking, walking, swallowing, and breathing.
The most common form of SMA is caused by a mutated or missing gene known as the survival motor neuron gene 1 (SMN1), which is typically responsible for the production of a protein essential to motor neurons.
The most common form of SMA is caused by a mutated or missing gene known as the survival motor neuron gene 1 (SMN1), which is typically responsible for the production of a protein essential to motor neurons.
People living with SMA have insufficient levels of the SMN protein, which leads to loss of motor neurons in the spinal cord and causes weakness and wasting of the skeletal muscles. The weakness is often more severe in the trunk (chest) and upper leg and arm muscles than in muscles of the hands and feet.
Carrier frequencies in most populations are estimated at 1 in 40 to 1 in 60.
A blood test is available to look for mutations or deletions of the SMN1 gene. This test identifies at least 95% of SMA.
Fragile X
Fragile X syndrome results from mutations in a gene on the X chromosome.
It is the most commonly inherited form of developmental and intellectual disability.
This mutation affects how the body makes a protein called FMRP. When there is not enough FMRP produced the child will develop symptoms of Fragile X. The symptom of Fragile X correlates with the level of FMRP underproduction. Not everyone with the mutated FMR1 gene has symptoms of Fragile X syndrome, because the body may still be able to make enough of the protein FMRP.
Being female…
Females have two X chromosomes (XX), while males have only one. In females, if the FMR1 gene on one X chromosome has the mutation, the FMR1 gene on the other X chromosome might not have the mutation. Even if one of the female’s genes has a very large mutation, the body can usually make at least some FMRP, leading to milder symptoms.
Females have a 50/50 chance to pass it along to both their sons and daughters.
Males will pass it down to all of their daughters and not their sons.
People with Fragile X do not all have the same signs and symptoms, but they do have some things in common. Symptoms are often milder in females than in males.
Intellectual functioning
- These problems can range from the mild, such as learning disorders or problems with mathematics, to the severe, such as an intellectual or developmental disability.
- The syndrome may affect the ability to think, reason, and learn.
- Because many people with Fragile X also have
- attention disorders
- hyperactivity
- anxiety
- language-processing problems
A person with Fragile X may have more capabilities than his or her IQ (intelligence quotient) score suggests.
Physical Appearance
Most infants and younger children with Fragile X don’t have any specific physical features of this syndrome.
When these children start to go through puberty, however, many will begin to develop certain features that are typical of those with Fragile X:
- narrow face
- large head
- large ears
- flexible joints
- flat feet
- prominent forehead
Behavioral, social, and emotional
Most children with Fragile X have some behavioral challenges.
- They may be afraid or anxious in new situations.
- They may have trouble making eye contact with other people.
- Boys, especially, may have trouble paying attention or be aggressive.
- Girls may be shy around new people. They may also have attention disorders and problems with hyperactivity.
Speech and language
Girls usually do not have severe problems with speech or language, however most boys with Fragile X have some problems with speech and language.
- They may have trouble speaking clearly, may stutter, or may leave out parts of words.
- They may also have problems understanding other people’s social cues, such as tone of voice or specific types of body language.
- Some children with Fragile X begin talking later than typically developing children. Most will talk eventually, but a few might stay nonverbal throughout their lives.
Sensory
- Many children with Fragile X are bothered by certain sensations, such as bright light, loud noises, or the way certain clothing feels on their bodies.
- These sensory issues might cause them to act out or display behavior problems.
What can be done if we are Carriers?
If you and your partner discover through genetic testing that you are both carriers for the same genetic disease before pregnancy or early into pregnancy, one of our specialist at County Obstetrics and Gynecology can discuss with you your options and help you make the right decisions for your family. You have a few different paths you could take.
Consult a specialist
If the condition you carry can be treated, find a specialist who can help evaluate and treat your baby right after delivery.
Consider In Vitro Fertilization (IVF)
Some couples can minimize their risk of passing on harmful genes by working with a fertility specialist. With in-vitro fertilization, you may use an egg or sperm from a donor or use preimplantation genetic diagnosis. This is a technique in which a specialist grows several embryos in the lab and then implants the one(s) with the healthiest genes in your womb.
Perform a prenatal diagnosis
If you are already pregnant, your doctor can perform a test to check for the presence of genetic diseases.