Handbook of Genetic Counseling/Cystic Fibrosis - Prenatal Diagnosis-2

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Cystic Fibrosis - Prenatal Diagnosis

Introduction and Contracting[edit | edit source]

  • Acknowledge any prior contact
  • Ask them what they hope to gain from the session
  • Do you have any particular questions you would like to discuss?
  • Address any immediate concerns or indicate that they will be addressed later during the discussion
  • First I'll obtain more information about medical and family history
  • Then review CF and discuss family planning options including prenatal testing and PGD

Obtain Medical and Family History[edit | edit source]

  • Ask them to describe their experience with receiving a diagnosis of CF in their daughter
  • What type of testing did your daughter receive to confirm diagnosis?
  • Were the mutations identified?
  • Were there any complications with the pregnancy?
  • Have you had any other pregnancies?
  • I'm going to take a family medical history. Some of the questions I will ask will help us determine if there are any other hereditary disorders that we may want to discuss

CF[edit | edit source]

  • You seem to have a lot of experience with CF how do you feel about your chances of having another child with CF?
  • Get them to explain their understanding of their risks
  • AR inheritance (1 in 4 of having CF and ½ or 50% chance they will be a carrier)
  • Any questions about the genetics or biological cause of CF?

Facts About CF[edit | edit source]

(I don't think it will be necessary to review all of this because they probably know more than I do about CF, but this is for my benefit)

What is it?[edit | edit source]

  • CF is one of the most common inherited diseases (affects 1 in 3300 live births in US)
  • most common in Caucasians
  • multisystem disease affects resp. tract, pancreas, intestine, reproductive tract, hepatobiliary system
  • causes body to produce thick mucus lead to pneumonia, diarrhea, poor growth, and infertility
  • due to faulty transport of sodium and chloride within cells lining certain organs

Features of CF[edit | edit source]

  • normal intelligence
  • features may include
  • chronic sino-pulmonary disease: cough, sputum production, wheezing, obstructive lung disease, chronic chest radiograph abnormalities, digital clubbing
  • gastrointestinal/ nutritional abnormalities: malabsorption/ pancreatic insufficiency (foul, bulky, fatty stools) distal intestinal obstructive syndrome, rectal prolapse, recurrent pancreatitis, chronic hepatobiliary disease, failure to thrive, hypoproteinemia, fat soluble vitamin deficiencies
  • infertility: 98% of males with CF infertile due to unilateral or bilateral agenesis of vas deferens

decreased fertility in females due to abnormal cervical mucus that can contribute to infertility

Diagnosis[edit | edit source]

  • median age diagnosed = 6-8 months (2/3 dx before age 1)
  • diagnoses established in people with one or more phenotypic features and one of following
  • presence of 2 disease-causing mutations in the CFTR (cystic fibrosis transmembrane regulator) gene
  • two abnormal quantitative sweat chloride values (the "gold standard")
  • painless, relatively inexpensive, definitive answer)
  • abnormal value for the transepithelial nasal potential difference (NPD)
  • diagnosis established in absence of phenotypic characteristics when
  • confirmed dx of sibling and abnormal sweat chloride value or presence of same two mutations as in the sibling

Prognosis[edit | edit source]

  • survival increased from 18 years 1976 to 30.1 years 1995 currently approximated at 33 yrs (geneclinics)
  • pulmonary disease major cause morbidity and mortality
  • patients with pancreatic sufficiency (<10%) have milder course and greater survival (56 yrs 1995 CFF Patient Registry
  • wide variability in disease expression

Incidence[edit | edit source]

  • Caucasians 1/2,500
  • African-Americans 1/18,000
  • Asian Americans 1/90,000
  • 30,000 affected in US 8,000,000 carriers in US
  • carrier rates see chart in visual aids

CF gene and common mutations[edit | edit source]

  • located on 7q
  • 250,000 bp, 27 exons and 1,480 aa's
  • functions as a regulated chloride channel in epithelial cells
  • over 900 known mutations (most point mut. or small del.)
  • genotype/phenotype correlation (both severe and mild mutations)
  • delta F508 most common (30-80% of mutations)
    • Later on we will be discussing what testing is available for family planning and CF testing. This same prenatal testing can detect some birth defects and chromosomal abnormalities also.

Explanation of Advanced Maternal Age[edit | edit source]

  • As women get older their risk for having a baby with a change in chromosome number increases. There is no magic age at which a woman goes from no risk to high risk. However, at age 35 the risk is considered high enough to offer some standard testing options that we will discuss today.
  • Explain chromosomes and genes
  • Explain nondisjunction
  • Briefly describe the common trisomies (21 (Down Syndrome), 18, 13, 47XXY)
  • Chance of having a baby with one of these chromosomal changes increases with maternal age

Chromosome abnormalities[edit | edit source]

(Details I won't go into very much again fro my benefit)

  • Explain nondisjunction
  • This mistake that occurs in cell division is a random chance event that does not run in families
  • Although it is a random event, it does occur more often as a woman gets older
  • When there is an extra copy we call it trisomy because there are three copies instead of the usual two copies
  • Any time there is extra genetic material there are changes in the way the fetus grows and develops

Down Syndrome[edit | edit source]

  • The most common type of trisomy is called Down Syndrome or trisomy 21 because it is caused by an extra copy of chromosome 21
  • You mentioned a distant cousin with Down syndrome-- how familiar are you with this condition?
  • Children with Down syndrome are all unique, but often have distinguishable physical characteristics that you might recognize.
  • They are all mentally retarded and this is most often mild to moderate
  • They also often have heart defects and are at an increased risk for some other specific medical concerns

Trisomy 18, 13[edit | edit source]

  • Two of the other common trisomies are trisomy 18 and 13.
  • Children with these conditions are more severely affected than those with Down Syndrome.
  • They usually have a variety of birth defects and are severely mentally retarded.
  • Many miscarry and those that are born often do not live past 1 year of age

Other chromosome abnormalities involving the sex chromosomes[edit | edit source]

  • Other chromosome abnormalities that you may be at an increased risk for involve the sex chromosomes
  • Babies can have an extra copy of one of the sex chromosomes and sometimes you can't even tell
  • They may have learning disabilities.
  • They don't have increased risks for severe medical complications, but may be infertile.

Age Related Risks[edit | edit source]

  • Age related risks (refer to chart in visual aids)
    • Age 38 risks
    • Live born baby with Down Syndrome 1 in 189 or 0.53%
    • Live born with chromosomal abnormality 1 in103 or 0.97%
    • chance of having a liveborn child with normal chromosomes is 99.03%

Prenatal Testing Options[edit | edit source]

  • 2 are diagnostic tests (CVS and amniocentesis) which will tell you with nearly 99.7% certainty if the fetus has one of the chromosomal changes discussed and almost 100% certainty whether the fetus has CF
  • Ultrasound will help in determining the overall development of the major organs and can show some birth defects (may show fetal echogenic bowel and/or dilated bowel which can be an indication of CF)

Chorionic Villus Sampling Overview[edit | edit source]

  • Often referred to simply as CVS
  • CVS is a technique in which a sample of placental tissue is obtained
  • The little fingerlike projections of the placenta that are sampled are called chorionic villi
  • The villi are derived from the same original cells as the fetus so these cells should have the same genes and chromosomes as the fetus and we can look at the chromosomes in these cells and detect the chromosomal abnormalities discussed earlier
  • CVS is performed between 10 and 12 weeks gestation
  • CVS has been around since 1983 in US

Amniocentesis Overview[edit | edit source]

  • Have you heard about amniocentesis?
  • It is a simple medical procedure that is usually performed after 15 weeks gestation that is used to rule out many chromosomal abnormalities including the ones we just discussed that you are at increased risk for
  • A small sample of the amniotic fluid that surrounds the baby is taken
  • Within the fluid are skin cells that have been sloughed off by the baby.
  • These cells can be grown in a lab and then the chromosomes can be looked at

Amniocentesis VS. CVS[edit | edit source]

  • Review visual aid that compares the two procedures on timing, risk, accuracy etc.

What Information These Procedures Can Provide[edit | edit source]

  • determine if the fetus has one of the chromosomal abnormalities we discussed with >99% accuracy for amnio and 98-99% accuracy for CVS
  • DNA obtained from the sample can also be used to test for CF with almost 100 % accuracy
  • determine the babies sex if you would like to know.
  • The fluid obtained during an amnio also used to test for open neural tube defects such as anencephaly and spina bifida, but CVS can't (should have blood test)
    • Spina bifida is where the spinal cord didn't form properly and nervous tissue is exposed
    • It can cause motor impairments along with other health concerns
    • Risks for these do not increase with age, but it is tested for at the same time and the test is able to detect 99% of ONTD's (if measuring AFP and acetylcholinesterase)
  • CVS does not test for NTD's Therefore it is recommended that a woman has a blood test at about 16 weeks to determine if the fetus is at increased risk for a neural tube defect

Limitations[edit | edit source]

  • Most birth defects cannot be detected by amnio or CVS. (Amnio can detect about 10% of birth defects including the ones we discussed).
  • For example cleft lip, cleft palate, congenital heart defects, small chromosomal abnormalities, and many types of mental retardation will not be detected.
  • Doesn't routinely test for other heritable disorders unless ordered specifically
  • Most women tested receive news that their child doesn't have chromosomal abnormalities but it doesn't guarantee a healthy baby. (3-5 out of every hundred babies has a birth defect).

There are some risks associated with the procedures[edit | edit source]

  • .5% additional risk for pregnancy loss with amnio (1 out of every 200 women who have an amnio will have a miscarriage that is due directly to the procedure) 1% with CVS These risks are above the baseline risk of miscarriage that all women have.
  • Life threatening problems to the mother are extremely rare
  • Infection can occur but rare (less than 1 in 1,000 women)
  • Blood group sensitization (Rh - mothers will receive RhoGam following procedure)
  • Routine amnio is not associated with increased risks of birth defects in the fetus
  • Scarring of the baby is possible but is thought to be very uncommon
  • Extremely low risk of uterine infection
  • Some studies reported a possible risk of limb defects with CVS while other studies have not. Most of the defects were noted if the procedure was performed before 10 weeks because the limbs develop between 4-10 wks. If there is an increased risk it is about 1 in 3000.
  • Risks are lower if the physician is highly experienced
  • There is a very small chance of lab error and the need to repeat the procedure
  • CVS has higher risk of error 1-2%

Reasons some women choose CVS[edit | edit source]

(This is a personal decision and each woman places different emphasis on the things that are important to her)

  • Permits termination at earlier gestational age
  • 1st trimester and people often don't know that she is pregnant
  • Early termination has been reported to be easier emotionally and physically
  • Allows treatment for a fetus with 21-hydroxylase deficiency (CAH) autosomal recessive condition in which shots of dexamethosone can be given
  • They want reassurance that the fetus does not have a chromosomal abnormality

Reasons some women choose amniocentesis[edit | edit source]

  • Lower risk of pregnancy loss 0.5% instead of 1%
  • Results are slightly more accurate >99% compared to 98-99%
  • Offers detection of open neural tube defects (90-96%)
  • However, a maternal blood test (MSAFP) can be performed later in pregnancy (14-22 wks) and will detect 85% of open NTD's
  • Procedure is easier and more hospitals perform it
  • With CVS there is a greater likelihood of needing further testing due to
    • Laboratory failure
    • Maternal cell contamination
      • Frequency 1.9%
      • Not problematic for cytogenetics, can be for DNA or biochemical testing
      • Can be detected by DNA analysis using a maternal blood sample
    • Mosaic or ambiguous results
      • Presence of two or more groups of cells that differ in their chromosome make up
      • Occurs in 1-2% of CVS samples
      • less concerning in CVS than amnio because the placental cells are more distantly related they split off from the cells in the embryo early on so fetus might not share same genetic make up
    • Insufficient sample
  • They want reassurance that the fetus does not have a chromosomal abnormality

Reasons some women choose not to undergo either procedure[edit | edit source]

  • They don't want to take that added risk of miscarriage
  • They are more anxious about the procedure than they are about having a child with a chromosomal abnormality
  • They feel comfortable not knowing if there is one of these problems until they deliver the child
  • They don't feel a need for reassurance and would not abort the fetus regardless of the result
  • Moral or religious views

Detailed description of the amnio procedure[edit | edit source]

(I WON'T go into this much detail)

  • Spend more time on the procedure details if she is interested or if needed to make an informed decision
    • The entire procedure from when you arrive to when you leave will last about 20-45 minutes and you can return home after it is completed
    • Some physicians require you to have a full bladder
    • Abdomen is cleaned and sterilized
    • A local anesthetic is often given to numb the outer layers of skin (this is similar to the shot your dentist uses)
    • Ultrasound is used before and during the procedure to visualize where the baby is and find a pocket of fluid.
    • A needle about the width of a needle used to draw blood, but longer (3") is inserted through the abdomen into the uterus and amniotic sac.
    • The needle may seem long but it is the width that is felt
    • The needle is only in for one or two minutes while amniotic fluid is drawn up through it.
    • Most women report that the needle insertion is not as painful as they had expected, but that there is some discomfort.
    • Some report a stinging sensation when the needle first enters the skin
    • Some report that they feel a sharp pain or a contraction as the needle enters the uterus.
    • Others describe it as feeling similar to blood draw.
    • Some experience a sensation of pressure in their lower abdomen as the fluid is drawn up through the needle.
    • It is also common for women to report some minor uterine cramping (similar to menstrual cramps) during and/or after the procedure.
    • Usually the first little bit of fluid is discarded because it might have some of your cells mixed in.
    • The sample will be about 20cc or 1-2 tablespoons. This fluid is quickly replaced by the baby.
    • The babies heart is monitored by U/S after the procedure

What to expect and do after the amnio[edit | edit source]

  • Mild cramping is common
  • Spotting occurs in a small percentage of women
  • After the test avoid strenuous activities for 24 hours
  • Call the doctor immediately if you experience any of the following:
    • severe and persistent abdominal pain and cramps
    • vaginal bleeding
    • vaginal leakage of amniotic fluid
    • anything that seems unusual
  • The results will be available in about 1.5 to 2 weeks

Description of CVS[edit | edit source]

  • There are two ways the procedure can be performed: Transcervical and Transabdominal
  • Contraindications for both types include:
    • Active vaginal bleeding (must have stopped at least 1 week ago)
    • Rh sensitization (if already sensitized) if not sensitized Rhogam given to Rh negative women to prevent sensitization
    • Maternal bleeding disorder
    • Fibroids not avoidable
    • Multiple gestation? (usually not attempted)
  • Transcervical
    • Procedure is similar to a pap smear
    • Vagina and cervix are cleaned
    • Under the visual guidance of ultrasound, a thin tube (catheter) inserted through the vagina, cervix, and into the placenta
    • Once the catheter is in place a syringe is attached
    • Suction is applied to remove the villi while the catheter is removed
    • After the sample is obtained it is viewed under a microscope to be sure the size and quality is sufficient and another sample is not needed
    • Sample is placed in a tube of tissue culture medium and sent to a lab for testing
    • Most women report minimal discomfort during the procedure although it varies
    • The actual procedure only takes about 5 minutes
    • The baby's heart beat will be monitored
    • Bleeding occurs in up to 10% of women
    • (Easiest to perform with posterior placenta close to cervix)
    • (Contraindications for transcervical CVS include: cervical polyps, overly curved sampling pathway, active genital herpes or other infections)
    • (Large sample is obtained including whole villi)
  • Transabdominal
    • Abdomen is cleansed and xylocaine injection is given to numb the upper layers (similar to shot given at the dentist)
    • Using ultrasound as visual guidance, spinal needle is guided through the abdominal wall, uterine wall, and into the placenta
    • Once in place a syringe is attached to supply suction
    • While suction is supplied the needle is moved back and forth through the placenta
    • After sample is obtained it is viewed to make sure there is enough and another sample is not required
    • Sample is then placed in a tube of tissue culture medium and sent to a lab for testing
    • There is a wide range of responses when it comes to how women report the procedure felt. When the needle is inserted it may burn for a few seconds. Women report everything from mild cramping to painful, heavy cramping.
    • The actual procedure takes about 5 minutes
    • The heartbeat of the fetus will be monitored
    • Bleeding is rare
    • Contraindications for transabdominal CVS include: interceding bowel, the placenta is too far from the maternal abdominal surface (obesity)
    • (Easiest to perform with anterior or fundal placenta)
    • (Smaller sample size (pieces of the villi) obtained)
    • (Can be performed after 12 weeks, but usually only if there is not enough amniotic fluid for an amniocentesis)

Recommendations for after the procedure[edit | edit source]

  • No exercise or strenuous activity for 24 hours
  • No sexual intercourse, douching, tub baths, or tampon use for 72 hours
  • Notify the OB in any of the following occur:
    • Fever greater than 100.4 degrees F
    • Heavy bleeding or cramping
    • Amniotic fluid leakage
  • Return for follow up ultrasound (if that is standard practice)
  • Blood test (MSAFP) at 16-18 weeks to check for NTD's
  • Ultrasound is recommended at 18-20 weeks

Test Results[edit | edit source]

  • Results will be available anywhere between 1-2 weeks depending on which lab it is sent to (Genzyme 7 days, CHMC about 2 weeks)
  • More than 95% of women receive reassuring news
  • Remind them that sometimes further follow-up testing is needed
  • Ask them how they would like to receive their results and if they want to know the sex of the fetus

Preimplantation Genetic Diagnosis[edit | edit source]

  • Performed at only few centers in US
  • Closest is Regional Genetic Institute in Chicago
  • First attempt in 1989
  • Can be used to detect any genetic condition for which there is a sufficient sequence information
  • Can detect common aneuploidies and translocations
  • As many as 40 PGD centers have been established in 17 countries
  • By this time, these centers performed approximately 3,000 clinical cycles, resulting in more than 500 pregnancies (over 20% pregnancy rate), and the birth of nearly 300 healthy children.
  • More than two thirds of these clinical cycles were performed in USA, from which the largest number (1,200 cycles) was contributed by RGI. This resulted in 250 pregnancies and birth of approximately 200 healthy children
  • At present, RGI (Chicago) is the only center in the world offering Preimplantation Diagnosis by sampling the first and second polar bodies.
  • he first polar body is discarded during oocyte maturation, prior to fertilization and contains one set of duplicated chromosomes
  • the second polar body is discarded after fertilization and contains one set of chromatids
  • test the polar bodies for genetic disease to determine if egg has mutation
  • offered to couples who are known carriers of genetic diseases detectable by DNA analysis
  • RGI physicians have already performed over 100 clinical cycles involving preimplantation diagnosis many genetic diseases including CF
  • diagnosis of Down syndrome and other common aneuploidies
  • analysis of the chromosome number (13, 16, 18, 21) in both the first and second polar body by FISH
  • Only embryos resulting from the fertilization of eggs with normal number of these particular are transferred
  • patients may choose which embryos they wish to be transferred or frozen. The procedure has been offered to over 600 IVF couples
  • resulted in 131 births of healthy children and dozens ongoing pregnancies confirmed to be unaffected by CVS or amniocentesis
  • Preimplantation diagnosis via blastomere biopsy is also performed for other specific disorders involving paternal genes or sex selection for X-linked disorders and if doing IVF cycle outside of
  • Cost (probe development $1,000, PGD for one cycle $3,000, IVF one cycle $7,500 IVF meds $2,000-$4,000, cost to send embryologist to your IVF center $2,000 Total $13,500-$17,500 per cycle

Review[edit | edit source]

  • Assess if there are any questions or other concerns throughout the session
  • Assess again how she feels about the test options
  • Offer patient literature (already sent according to chart note)

References[edit | edit source]

Notes[edit | edit source]

The information in this outline was last updated in 2000.