Topic 1: Common prenatal screening for genetic or chromosomal diseases
1. a. Ultrasound images show that a fetus is in the breeched position late in the pregnancy. Will this yield a false positive, or a false negative, result (choose one of the two) when evaluating nuchal translucency for disease? Support your choice with good logic/good science.
b. In “a” above, would the PAPP-A / IGF interaction help you with your choice? Yes or no? Support your “yes” or “no” response with good logic/good science.
2. Choose an anterior lobe pituitary hormone which influences any aspect of pregnancy. Propose how HYPOPRODUCTION of this hormone influences the interaction between PAPP-A and IGF.
3. A quad screen is done on a pregnant lady. Her ovarian and placental outputs are abnormal, causing abnormally high estriol and abnormally low HcG. Which of the four aneuploid diagnoses would this influence the most? Support your answer with good logic.
4. PGD works for obtaining a pre-implantation diagnosis of a genetic disease. A polar body analysis is not as good because you only get information from one parent. Propose one reason why a polar body analysis would be beneficial for diagnosis of Turner’s syndrome (the female has only one X-chromosome instead of two).
Topic 2: PUBS
5. Suppose the fetal umbilical vein is positioned so it is not accessible to PUBS. Although the liver, and its associated vessels, is big and accessible, it is best not to draw blood from this vital organ. So, suggest another place (besides the umbilical cord vessels and the liver/liver vasculature) in the fetus where blood may be safely withdrawn. Give a sound anatomy and/or physiology reason why you have selected this area.
6. Banked cord blood is mainly used to treat a disorder in the person it came from. Of the following disorders, choose the one you think will be most amenable to cord blood stem cells: Alzheimer’s disease, acute myelogenous leukemia, a blocked coronary artery.
Topic 3: In utero surgery and prenatal medicine
7. In utero surgery can be done either “closed” or “open”. If you are treating polycystic kidney disease, which of the two would you use, and why? Of course, provide good reasons for your choice.
8. Which other human disease would the “Baby Grace” procedure be a good choice for treatment? Support your answer with good science.
(Topic 1) Prenatal and pre-implantation genetic diagnosis
Prenatal genetic screening and diagnosis
WAIT A MINUTE — Why are we are doing THIS topic before anything else??? Where’s the Genetics??? To answer that question, you are about to experience an example of my amazing organizational skills. One of the most significant goals of molecular genetics is clinical diagnosis. Obviously, the earlier a disease can be diagnosed, the better it can be managed, treated, or even cured. In order to diagnose a fetal genetic disease using molecular techniques, you must obtain a viable, representative cell/tissue sample. So, if the sample is needed prior to the molecular diagnostics, then it makes sense to look at some prenatal sampling techniques before we dive into any genetics. How’s that for impeccable logic???
First, let’s be sure we know the difference between screening and diagnosis.
A screening test assesses a baby’s statistical risk for a particular condition. Comparison is made between the baby’s risk, and the occurrence of that condition in the general population. Screening tests include both anatomical and chemical analyses:
1. General ultrasound.
2. Three-dimensional (3-D) ultrasound
3. First trimester and second trimester tissue sampling
4. Nuchal translucency ultrasound (described later in this section)
6. Testing Mom’s blood (maternal serum testing) during a pregnancy.
A diagnostic test is performed to see if a condition is actually present or absent. It should be clear that the five listed above can also double as diagnostic tests. However, the classic diagnostic tests include amniocentesis and chorionic villus sampling. Both of these are described later on. There is also pre-implantation genetic diagnosis (PGD), which is a more elegant diagnostic test than the others. Although PGD comes with some ethical and moral baggage, it is A REALLY COOL way to diagnose a disorder.
Common prenatal screening for genetic or chromosomal diseases
Screening must start with an assessment of the physical and/or chemical makeup of the patient. This course contains significant sections dealing with chemical analysis of DNA, RNA, proteins of every size and shape, and blood. We will deal somewhat less with physical analysis, but it still needs to be part of gathering data for screening. This means that screening must be done prior to diagnosis. And yes, fetal tissue can be obtained and screened.
In order to perform the chemical analyses, you have to be able to obtain tissue samples. We know that these samples may be obtained from adults, children, babies, and developing fetuses. Wouldn’t it be nice if we could analyze the zygote? Well, we can, but then there really would be nothing left to develop. But, you know what? We can go one better than that! These samples may be obtained from YOUR baby BEFORE you even get pregnant! Prezygotic ??? That’s right! We’ll see how later. Anyway, the earlier you get your tissue sample, the better will you be able to socially and otherwise deal with abnormalities. So, let’s concentrate on seeing how early we can get these samples, and then talk about how to analyze them with various screening tests.
There is really no way to even give you the headline version of all the sophisticated tests now available to screen for genetic/chromosomal disorders in the fetus. So, this discussion will center around two very versatile tests:
(1) First trimester integrated screening, which combines the physical information from ultrasound with the chemical information provided by the PAPP-A / IGF interaction, and hCG screening.
(2) Quad screening, which gives you a result based on the levels of four biochemical markers.
First trimester integrated screening
The “first trimester integrated screening” provides screening for a condition called Down’s Syndrome (trisomy-21), marked by an extra chromosome in most of the individual cells. It is the most common chromosomal anomaly, and will be discussed in more detail during week 6. With this test, the detection rate is 85% with a false positive rate of only 5%.
Two tests, which can be performed as early as week 8 of a pregnancy, are combined to screen for Down’s Syndrome:
1. Cordocentesis, followed by chemical analysis
2. Routine ultrasound with nuchal translucency analysis
(1) A blood sample is obtained from the fetal umbilical cord. The “tried and true” name for this process has been “cordocentesis”. The more modern name is Percutaneous Umbilical Blood Sampling (PUBS). The blood sample is taken so that the level of PAPP-A (pregnancy-associated plasma protein-A), IGF’s, and hCG (free-beta human chorionic gonadotropin) can be assessed.
PAPP-A controls the levels of a family of growth factors in the placenta, the insulin-like growth factors (IGF’s). For a very comprehensive look at the significant role of IGF’s in fetal development, please go to the following link:
IGF’s and fetal development
After reading all of that information it is clear that IGF’s have a major role in every stage of fetal development. And PAPP-A controls/stimulates the production of IGF’s!!! Women who smoke are more likely to produce a small amount of PAPP-A. The role of PAPP-A in the well recognized association between smoking and low birth weight seems very clear.
So, where does that leave us? Traditionally, using Down syndrome as an example, screening for low-risk pregnancies has been performed on maternal serum in the second trimester. When second trimester screening identifies a pregnancy at increased risk for Down syndrome, the woman is offered amniocentesis to investigate the fetal chromosomes. The first trimester only screen has increased the detection rate of Down syndrome to 85%, while providing results earlier in the pregnancy so that a woman may have the choice of confirmatory chorionic villus sampling or amniocentesis, or terminating the pregnancy.
Free beta Human Chorionic Gonadotropin is the hormone that your home pregnancy test is looking for. So, the smiley face/sad face (or whatever), in these kits, is a specific chemical test for the hormone hCG. Why? hCG specifically targets the corpus luteum, (1) preventing its degeneration, and (2) allowing it to keep the level of progesterone high, so that the stratum functionalis of the uterus is not shed**. Put another way, elevated levels of progesterone prevents menstrual bleeding from occurring. As such, it is produced very soon after fertilization, and only when fertilization occurs. hCG levels normally double every two to three days. However, if you have been given an hCG injection (which exists as pharmaceuticals called “Profasi” or “Pregnyl”), to lengthen the ovulatory stage of your cycle, investigators need to know this, since it can stay in your system for a while, and result in a false positive.
**(Do you need to review the anatomy and physiology of the uterus? And how it responds to hormones? This would be a good time (go ahead, I’m not watching).
2) Nuchal translucency refers to the swelling just under the skin at the back of the fetal neck. It is easily visible with a slight adjustment to routine ultrasound. It is important because if the fetus has a greater-than-normal amount of swelling at the back of the neck, there is a high likelihood that the baby will have Down Syndrome, or a major heart problem, or both. The physical evidence provided by nuchal translucency, and the chemical evidence provided by quad screening (discussed in the next topic) are the current standards used to screen for Down’s Syndrome. Nuchal translucency testing is also used to detect a number of neural tube defects, such as anencephaly and spina bifida. Nuchal translucency ultrasound has to be done a little later — between 11 and 13 weeks, which means it might have to go into the beginning portion of the second trimester. The reason for this is that the swelling occurs normally in most births as a transient condition, and is gone by week 14. Persistence past that point is abnormal.
The following is an ultrasound photo showing the fetal nuchal translucency:
You can see, marked by two little crosses, one on top of the other, the area of the posterior fetal neck. This shows the swelling nicely. The 0.21 cm length happens to be within the normal range.
Three-dimensional (3-D) ultrasound
As long as we are talking about ultrasound, 3-D ultrasound really presents a clear picture of the baby’s gross anatomical features. This is shown by the picture belo
Very nice picture! Many genetic disorders have characteristic anatomical abnormalities. of the face, head, and/or skull. That is NOT the case with this baby, but if there were any such anomalies, a 3-D ultrasound would show them very clearly.
As the name certainly implies, there are four analytes involved in this test. For the most part, the information revealed by using this combination of tests concerns open neural tube defects (ONTD’s), Down’s syndrome, and another fairly common chromosomal disorder called Trisomy 18 (three copies of chromosome 18 are present in most cells). Until recently, triple screening using a combination of three tests (the first three of the four listed below) was the standard. A fourth test has been added.
Interpretation of quad screening
An aneuploidy occurs when an individual has an extra chromosome. So, given that all chromosomes are normally in pairs, aneuploid conditions occur when one of these pairs has an extra member, making three chromosomes instead of an normal pair. For example, three copies of chromosome 21 results in a condition called Down’s Syndrome.
The following table shows the results of the testing, and the most probably diagnoses. “Aneuplodies” are abnormal chromosome numbers associated with particular diseases. There will be a more detailed discussion of these later in the course, but for now, here is how these four tests screen for the four most common human aneuploidies.
(1) Alpha-fetoprotein (AFP) is synthesized by the fetal yolk sac and liver, and is normally found in the serum. It usually winds up in the kidneys and lungs where it is excreted from the body. Since the neural tube in ONTD’s is open, large volumes of AFP gain access to the amniotic fluid. This AFP then passes from amniotic fluid to maternal blood where increased amounts are detected with maternal serum AFP (MSAFP) screening.
The one caution that has to be considered is that the gestational age has to be accurate. If the age is underestimated, then the AFP will be falsely reported as abnormally high. Given that this is correctly estimated, 70-80% of pregnancies affected with spina bifida, and 95% of anencephalic pregnancies, will have abnormally high levels of AFP in the maternal serum.
(2) Estriol (Unconjugated estriol or uE3) is the principal estrogenic hormone in the blood during pregnancy. uE3 is synthesized in the placenta shortly after it is formed. It exists in the maternal blood as a mixture of the unconjugated form together with a number of conjugates.
(3) Human chorionic gonadotropin (hCG) we have already discussed. It is a great screening AND diagnostic test. As we noted, it is synthesized by the placental trophoblast within a week after fertilization. Because of the amount of synthesis, maternal hCG levels rise very rapidly. So rapidly, as we mentioned previously, that it can be detected in urine samples within 7-8 days of fertilization by the home pregnancy tests. Even more astounding is that levels double every 2-3 days during the first six weeks of pregnancy! If the levels of hCG are significantly elevated at about the middle of the second trimester, this is an indication of Down’s Syndrome, or possibly trisomy-18.
(4) Dimeric inhibin A is synthesized in, and secreted by, both the placenta and corpus luteum. This one was added to the three tests given above to come up with the current quad screening analysis. Although dimeric inhibin comes in two types, A and B, only type A (DIA) is present in the maternal serum during pregnancy. Unlike the other analytes, DIA levels remain relatively constant between 15-20 weeks gestation. Increased DIA levels are associated with an increased risk for Down’s Syndrome.
It is truly amazing how much information can be obtained with a quad screen!
Common prenatal diagnosis of genetic or chromosomal diseases
Prenatal diagnosis is a term you have all heard before. When you hear it, you think of a pregnant woman having tests done on her fetus. Perhaps there is a serious genetic disorder running in the family whose symptoms are present at birth. Perhaps the condition is a genetic disorder, due to a faulty gene creating an enzyme deficiency, or other biochemical anomaly. The presence or absence of normal biochemical products, such as enzymes, is easily detected by biochemical assay of most body fluids, including amniotic fluid. One example would be a condition called phenylketonuria (PKU). PKU results when there is a deficiency of the enzyme phenylalanine hydroxylase, which normally converts phenylalanine to tyrosine. The absence of the enzyme causes two problems: (1) a deficiency of tyrosine, an important amino acid unto itself, but which also gives rise to a number of other vital substances, and (2) the accumulation of phenylalanine — if it cannot be broken down, a “backup” is created resulting in excessive accumulation. The amino acid is then converted to its ketone biproducts (phenylketones), which are potentially dangerous to the infant. The excess is excreted in the urine — “phenylketonuria”.
OK, enough of that! Most defects in biochemical pathways work this way: the “double whammy” of the lack of the next product, and the backup of the first one. Enzymes are required at all stages of the pathway. Any deficiency causes the two-fold “lack of- and backup” consequence.
Going up a level, perhaps the condition is caused by a chromosomal disorder. Either the chromosome number is incorrect, or the structure of one or more chromosomes is incorrect. Numerical chromosomal disorders increase with increasing age of one or both parents. We have already mentioned Down’s Syndrome, another condition amenable to prenatal diagnosis. The incidence of this condition increases almost 500-fold from the time a mother is in her 20’s to the time she is in her 40’s.
It is obviously important to a couple expecting a child to have the diagnosis done as early as possible. Consider the following true scenario, which is now a landmark case in the history of prenatal diagnosis:
In 1988, a couple in Israel was talking with their pediatrician about a genetic disorder running in their family called Tay-Sachs disease (TSD). This is condition that is present at birth, and there is no cure and no treatment. All you can do is watch your baby get progressively worse, and die by the age of three or four. The developing fetus lacks an enzyme called hexosaminidase A (HEX-A). HEX-A prevents the accumulation of compounds called GM2 gangliosides in the central nervous system. A deficiency of HEX-A allows these compounds to accumulate, and blindness, paralysis, and physical and mental deterioration follows. The gene position has been well-documented for a number of years, being located on the long arm of chromosome 15. After watching two of their children die from TSD, they asked their pediatrician what could be done. The first option offered was transabdominal amniocentesis. This is a “tried and true” procedure that has been routinely utilized now for almost 60 years. At 15 to 17 weeks into the pregnancy, the mother is taken into surgery, and a needle is inserted into her uterus. A sample of amniotic fluid is withdrawn, and the cells can be cultured. Genetic and/or chromosomal testing can then be done on these cells to verify the presence or absence of many enzymes, including Hex-A. The following diagram shows the procedure, and how it is performed.
Click on the following link to read all about amniocentesis:
This particular couple did not like that option, since she wasn’t enamoured with the “needle through the abdomen”. Also, if the outcome would be negative, 15 to 17 weeks into the pregnancy is a little late for a safe, therapeutic abortion, if, in fact, that was their decision. They asked their pediatrician if it could be done earlier.
The pediatrician now informed the couple about a procedure called transcervical chorionic villus sampling (t-CVS). This is a procedure that can be performed about 8 to 10 weeks into the pregnancy. It is still done in a surgery setting, but with a catheter inserted into the vaginal canal. (This still warrants an “ouch” even though there are no needles). Samples of the tissue forming the amniotic sac, whose outer layer is called the chorion, are taken. These cells can be cultured, and genetic and/or chromosomal testing can be done to verify the presence or absence of an enzyme, and/or the right number of chromosomes. The following diagram shows the procedure and how it is performed.
Click on the following link to read all about CVS:
Chorionic Villus Sampling (CVS) information
Although this really obviates any problem involving safety in therapeutic abortion, the couple still did not like having anything to do with surgery during the pregnancy. Again, they asked their pediatrician if it could be done earlier.
Talk about getting a diagnosis early………..
The pediatrician informed the couple about a new procedure called fetal cell sampling from maternal blood. At five or six weeks into any pregnancy, the heart is beating and blood is circulating throughout the fetal body. Some fetal red blood cells have already escaped into the maternal circulation across the placenta. So, if there were a way to differentiate between fetal red blood cells, and maternal red blood cells, all that would have to be done would be to take a sample of blood from Mom’s arm, and separate the fetal from the maternal erythrocytes. You would then be able to perform biochemical assay at 6 weeks into the pregnancy. This is obviously easier said than done. Considering the average erythrocyte count is in the range of 5.0 to 6.5 million cells per cubic millimeter of blood, this sounds like a daunting task. One positive is that A FEW fetal red blood cells are still nucleated. Immature fetal cells contain the cell nuclei needed for the assays — these include erythrocyte precursors such as normoblasts. The only problem is that adult bone marrow occasionally releases the same immature cells into adult blood. A procedure was in place, however, at that time, where the fetal cells could be separated from the maternal cells. Using a combination of fetal cell antigen detection (on the fetal cells only), and a procedure called “magnetic cell sorting”, a reasonable sample of fetal red cells may be obtained. The technology for this, as you can imagine, is quite complicated. We need go no further, but now, diagnostic information is available as early as the sixth week of gestation.
Back to our couple. They were STILL NOT satisfied. They asked their pediatrician to give them guarantees. They wanted to know if they could find out about their (that’s their OWN) baby PRIOR TO (!) the onset of the pregnancy. So, their doctor responded the way he should: we can’t do tests on a baby unless we have a baby to do tests on! Two weeks later, the couple got a call from their doctor, and he told them that it can be done. Here is how the procedure works:
1. Obtain an egg cell from the mother, and sperm cells from the father. Obtaining the egg cell from the mother involves hormone therapy, timing of her menstrual cycle, and, yes, a surgical procedure to extract the ovum. However, the couple did not object to this surgery, since she would not be pregnant at the time. Obtaining sperm cells from the father is a lot easier, since all that is involved is . . . . well, let me leave that to your imagination.
2. Once the cells are obtained, in vitro fertilization (IVF) is done. IVF is certainly not new. This procedure has been done for over half a century; the technology to do it correctly is well in place.
3. Once IVF is successful, and a zygote is formed in vitro, it is allowed to grow out to the eight-cell stage. At this point, those cells are called blastomeres.
4. Using a suction micropipette, one of the blastomeres is removed from the capsule that contains the eight cells. This blastomere may or may not continue to undergo cell division. If it does not, a number of mitogenic agents can be applied to it to encourage normal somatic division. Biochemical assay and/or chromosomal analysis can then be done on these cells the same way they are done on amniotic fluid, chorionic tissue, or fetal normoblasts. At this point, all of the blastomeres are still totipotent, which means that genetic differentiation hasn’t started yet, but transcription and translation has proceeded to the point where gene products may be analyzed.
In the diagram below, the pipette on the left uses a breath of suction to hold the blastomeres in place. The pipette on the right is pulling out one of the blastomeres for testing.
Now, before you proceed any further, look at the diagram above once more, and try to envision the diameter of the pipette on the right. The pipette pulling the blastomere out of the cell mass is one-fourth of the thickness of an average human hair. WOW!!!
5. Anyway, if the outcome is positive (normal enzyme present), the rest of the blastomeres can be implanted in the uterus, and a pregnancy can ensue. If the outcome is negative, no pregnancy has been initiated, so the laboratory container containing the other blastomeres can be discarded.
The name for this procedure is very scary: it is called “embryo biopsy”. The name I personally like BETTER is not used as much, but it is much more comforting: Blastomere Analysis Before Implantation (known by the very cool acronym: BABI). This gives a couple information about their baby prior to the onset of a pregnancy. So, a new definition is needed. Instead of “prenatal” diagnosis, we use the term preimplantation genetic diagnosis (PGD). Yes, we are actually getting information about a SPECIFIC baby before it enters the comfort of the womb.
Please go now to the following link. You can certainly read all the text, but be sure to view the video.
Preimplantation genetic diagnosis
Expanding on the previous article, there is one more way to procure tissue for PGD: polar body analysis. Polar bodies??? Remember what they are??? If not, look it up before you click and enjoy!!!
Polar Body Analysis
Go on to the next section which describes how a sample of fetal blood can be removed for testing.
(Topic 2) Percutaneous umbilical blood sampling (PUBS)
PUBS (percutaneous umbilical blood sampling), also called cordocentesis, was first attempted in the early ‘80’s. The technique involves the use of high resolution ultrasound to guide a long needle through the abdomen, procuring a sample of blood from the umbilical vein. This blood can be used for the same purposes as amniotic fluid, samples of the chorionic villi, or blastomeres.
Genetic and chromosomal disorders can be diagnosed using this procedure. However, we are playing around with puncturing the main oxygen delivery system – the umbilical vein – within the umbilical cord. Recall that this vein does what the pulmonary veins do in the adult. That is, returning oxygen-rich blood from an oxygenating surface (the lungs in the adult; the placenta in the fetus).
OK, there are risks associated with PUBS (some of them the same as with amnio- or CVS). The real advantage is that you are obtaining a sample of blood, which in many instances, can yield more information than some of the other tissues. The blood obtained from this source also has a large reservoir of “stem cells” (we will be addressing stem cells as a whole separate week later in the course). Another advantage involves the benefit of storing this umbilical cord blood containing these stem cells for later use in cellular therapy (a brief allusion is below, but also discussed in our week on stem cell technology).
What is really cool about this procedure is that, unlike any of the other lab procedures, the same techniques that remove blood from the cord, can also be used to deliver treatment to the fetus!
Fetal anemias can be treated, various hemoglobinopathies can be treated prior to the birth of the baby, and even transfusion can be done in case someone wasn’t paying attention to Rh incompatibility. Later on, we will talk about delivering “good” genes into a baby, and how this process might be one that is used as a delivery vector.
How about a little more of the specific anatomy and clinical details? As we briefly mentioned, the blood is actually obtained from the umbilical vein, usually just as it exits the placenta. This is the most accessible and least “mobile” point within the cord. The artery can also be used, but the diameter of the fetal vein is greater than that of the artery — a bigger target. Once the needle has been guided into the umbilical vein, fetal blood is aspirated into a syringe. In order to confirm that the sample is fetal in origin, the mean corpuscular volume (MCV) of the sample must be analyzed. The MCV of a sample of fetal blood should be above 100 fL. In adults, the MCV is smaller simply because adult erythrocytes are smaller than those in the fetus. The diagram below illustrates the procedure:
From this diagram, I think you can easily see how withdrawal of blood, as well as delivery of medicine, can be done the same way. By the way, the placenta is not labeled. The placenta is the flat structure to the left of the aspirating needle.
Complications/risks of percutaneous umbilical blood sampling (PUBS)
One big problem is that this procedure cannot be done before about 17 – 19 weeks into the pregnancy. So, you have to wait even longer than you do with amniocentesis. If diagnosis is the only goal, results can be obtained quicker than they can with standard amniocentesis, because blood analysis is much faster than tissue culture. So, there are timetable pros and cons. Of course, like with any invasive procedure on any sized human being, the most critical factor is safety. In Caucasian populations, the risk of miscarriage directly due to the procedure is about 2%. This is certainly unacceptable, but is really the only safe way to obtain a blood sample early enough to follow up with fetal therapy if needed. Some of the things that can happen are: bleeding from the puncture site in the umbilical cord, cord hematomas, transient fetal bradycardia, infection, and feto-maternal hemorrhage.
Minimizing and/or eliminating the risk
Look at the numbers – 2% is actually a higher risk than any of the tried-and-true procedures. Perhaps the safest thing to do is to use CVS or amniocentesis for diagnosis, and then use the umbilical vein as a method of treatment. Still, if PUBS is done, there is always the best benefit that was briefly mentioned above. Assuming stem cell research proceeds to the stage of general use (yes, that is another whole can of worms) having a sample of cord blood from the fetus holds great promise for treatment of the post-natal individual, meaning that delivery of treatment through the umbilical vein becomes unnecessary.
It is clear that PUBS has played a major role in the history of prenatal diagnosis and it is still the method of choice for lifesaving diagnostic AND therapeutic measures in a number of diseases. Other potential uses for PUBS include assessment of the fetal platelet count in cases of alloimmune thrombocytopenia and in idiopathic thrombocytopenia purpura. Platelets could then be delivered into the fetus via the umbilical vein.
A different kind of blood bank
Here is another corollary to this protocol. For many years now, the blood from the umbilical cord has been “banked” for later use. Many centers throughout the world can store cord blood, and all the marvelous cells it contains, for a myriad of clinical uses. Please click on the following link, and read the article.
As you scroll down, there are three places where it says “read more”. So, “read more” in all three of those places. Also,when you are finished with those, scroll down just a little further, and click on “learn more”. This provides some very interesting information. Enjoy this fascinating web site.
Banking cord blood
In the next section, we will briefly talk about some of the biochemical screening procedures that can be done with blood or other fetal tissue samples.
(Topic 3) Methods of in utero surgery and prenatal medicine
In utero surgery and prenatal medicine
Are you sitting down? I hope you are when you look at this photo:
Here is what happened above:
When surgery is done on a fetus in utero, the mother has to be given an “anti-labor” drug to make sure that the posterior pituitary doesn’t think it’s time to secrete oxytocin. Next, an incision is made in the uterus, and then the baby is gently removed. The baby is placed in a sterile field, and the operation is performed. The baby is then returned to the uterus which is sutured closed. The rest of the gestation period is then allowed to continue. What happened when this photo was taken, is that as soon as the uterus was opened, the baby shot out her arm, and grabbed the surgeon’s finger!!! She was probably thinking: “You’re not going to cut me, doc”. The photographer happened to be in the room taking pictures, and was certainly Johnny On The Spot.
The in utero fetus as a patient (really!!!)
For the last thirty years or so, a new field of medicine has been blossoming. This new field is called pre-natal medicine, and there are internships and residencies teaching in utero surgery. The physicians in this field work in a miniaturized environment applying microscopic and sub-microscopic treatments for some very devastating human diseases. As this field grows, the medical perception of the developing fetus is being seen in a new light. Also, the public perception of this previously untouchable world is also beginning to change. Prior to the 1980’s, fetal exploration technology could observe morphology-altering disorders, predict genetic disorders, and determine with relative certainty whether or not a pregnancy was “normal”. Opinions and counseling could be offered, but beyond that it was just wait-and-see.
Today’s practicing pre-natal physicians view the fetus as a patient. As with any other patient, the fetus is accessible for treatment. Cures and/or palliative measures are administered. Surgery can be performed on the fetus, and steps are being taken to somehow start preventive medicine protocols on these very special patients.
Of course, prior to any invasive procedures, the fetus is usually viewed with high resolution ultrasound. We have all seen those marvelous images, black-and-white though they may be, as they show the head, arms, legs, etc., of the fetus. Zooming in on those live images reveals the heartbeat, body fluid motion, etc. I would like you to read through the following description of obstetric ultrasound. It describes every aspect of the procedure, has some fascinating images to view, and talks about the safety of the procedure. There is even a way to listen to fetal heartbeats as they are picked up by the sound transducer that is part of the equipment. Please look at this when you really have the time to enjoy it!!!!
Click on the following link for this wonderful writeup:
Entering the “womb” presents some very unique challenges: this “patient” is six inches long, weighs about four to six ounces, and has an energy expenditure that approaches that of a chain-smoking couch potato trying to run a marathon. So, using a mathematical analogy, the size of the fetus is inversely proportional to the treatment risk presented (you OK with that? – math is not your favorite subject – too bad!!! think about it!!!). Those very same risk factors may also affect the surrounding mother. Traditional surgical tools cannot possibly transcend the triple environment of the mother, her uterus, and her fetus. Nevertheless, medical centers worldwide have developed the necessary tools to surgically treat fetal patients and have repaired defects that have previously been completely out of reach.
It all started in the early 60’s when the first fetal transfusion was performed to offset the affects of an Rh incompatibility that resulted in erythroblastosis fetalis. However, true surgery in the womb has only become “commonplace” in the last two decades. In the late 1980’s, the first true fetal surgery was performed. A 14-week old fetus was diagnosed with obstructive uropathy using high frequency ultrasound. The ureter, which conveys urine from the kidney to the urinary bladder, was completely blocked. This would normally result in the back-up of urine, kidney damage, and ultimately toxic death of the fetus. Various medicines were used to obviate the onset of labor, since all that probing in the uterus might fool the posterior pituitary into secreting oxytocin prematurely. A tiny endoscope was inserted through the fetal abdominal wall, up through the urinary tract, and into the offending ureter. The instrument dilated the ureter, and relieved the blockage, thus curing the condition. Perhaps you can (or — perhaps you can’t) visualize the diameter of such an endoscope, since the diameter of the fetal ureter is measured in fractions of centimeters.
This surgery was performed at Wayne State University, in what is now called the Center for Molecular Medicine and Genetics. Fetal Diagnosis and Therapy are their strong suits – yes, THERAPY on the fetus. Since then, operations to repair diaphragmatic hernias have been routinely performed on fetuses at WSU and other centers. Also called hiatus hernia, this condition is an abnormal hole in the diaphragm. Under the right conditions, the stomach and even the small intestine can retroflex into the thoracic cavity through this hole. In an adult, this surgery is not really a big deal — pull the abdominal contents back down into their proper cavity, and repair the diaphragm (OK, so it IS a big deal). In the fetus, however, if the digestive organs are in the chest, the lungs can’t develop properly, and may not even inflate. Lung hypoplasia may result, and the fetus will die.
So, how is it all done? Two protocols are employed:
1. The open procedure calls for cutting open the uterus. The fetus may be, and usually is, either completely or partially removed from the uterus. After the definitive procedure is performed, the fetus is tucked back in, and the pregnancy is allowed to continue to term. Please turn on your sound system, and watch this awesome video of open fetal surgery:
Click here to view an open fetal surgery
2. The closed in utero procedure calls for leaving the uterus and fetus intact, and illuminating the uterine cavity via fiber optics. Endoscopes — appropriately called fetoscopes — under the guidance of high frequency ultrasound are the tools of choice. The surgeon is fitted with a device that magnifies the field of vision within the uterus. Here are some actual in vivo fetoscopographies:
What about this kind of surgery for genetic disorders? A disease of the immune system called SCID (severe combined immune deficiency) results when both the T- and B-lymphocytes do not proliferate from their embryonic precursors (lymphoblasts). The deficiency is created by either an immature thymus gland and/or insufficient thymosine, both of which are necessary for proper T-cell development. The intestinal and various other tissues responsible for the maturation of B-cells are equally deficient. Despite the multitude of symptoms and causes, this is a disease caused by a single gene defect. This gene is located on the X-chromosome. The product of that gene catalyzes the pathways necessary to convert lymphoblasts to their mature products. Of late, this disease has been cured by gene therapy — in fact, it was one of the first ones treated by those methods.
Investigators at WSU diagnosed the condition in a 15-week old fetus using amniocentesis. Using the closed in utero procedure, bone marrow from the baby’s father was delivered to the fetal abdominal cavity three times in a two-week period starting during week 16. Certainly, the father is 50% genetically compatible with the fetus. Under normal circumstances, this would not be enough for a “match”, and a different donor would be sought. The immune system of the fetus, however, is not yet mature enough to “reject” the marrow, so it was tried. This is one of the benefits of treating fetuses in utero to try and cure this and other disorders of the immune system — “foreign” cells might be accepted because of the immunological immaturity. The outcome was positive — the pregnancy continued and the baby was born with perfectly normal white cell counts. In fact, her own bone marrow was subsequently tested, and the differentiation from hemocytoblast to mature lymphocytes was normal. A genetic disorder had been diagnosed, treated, and cured using prenatal medicine.
In addition to fetoscopes, today’s technology now has the ability to introduce cameras into the womb, so that photos may be taken before, during, and after the procedures. Miniature versions of scalpels, forceps, hemostats, clamps, and other instruments have also been developed to perform fetal surgery. In many cases now, the open technique is preferred, especially if a morphological defect is to be repaired. Most of the time, the fetus is completely removed from the uterus, laid beside the mother with the umbilical cord intact, and the surgery is performed as it would be on an adult patient. Virtually every organ system now has mass manufactured kits developed to work on the fetus. Shunts have been implanted in the fetal brain to relieve hydrocephalus, spinal cords have been repaired which ultimately would have resulted in spina bifida, renal polyposis has been alleviated, etc., etc.
Many genetic and/or chromosomal disorders result in morphological and biochemical problems which can be treated and cured this way. Unfortunately, many of these same disorders result in severe mental insufficiency which, obviously, does not lend itself to this kind of treatment. The philosophy, however, is clear — take care of the problem as early as possible. Diagnosis is now possible prior to the onset of a pregnancy — using gene therapy, treatment may also be possible in the very near future. We DO know that all kinds of sophisticated treatments and procedures can be performed during a pregnancy.
One genetic disorder commonly being treated by in utero surgery is spina bifida. This condition can also be caused by a number of different kinds of trauma, especially in utero trauma during a pregnancy.
Click on the following link to view a good writeup on surgery for spina bifida. This article also has the human interest and family situations and comments.
In utero surgery for spina bifida
Are you a fan of REALLY OLD movies? There was a movie in 1966 called “Fantastic Voyage”. It starred Stephen Boyd, Raquel Welsh, Donald Pleasance, Raquel Welsh, James Brolin, and Raquel Welsh. I have no bias on who my favorite character was in this movie.
Anyway, a submarine full of these folks was miniaturized to the point where it could be injected into the bloodstream of a patient. They had one hour to stay small — in that time, they had to get to the patient’s brain and destroy a blood clot. Needless to say, the ship and its crew were attacked by antibodies, blown away by pleural dynamics, and thrown all over the place when they entered the heart. This is science fiction. About 30 years ago, everything we have talked about in this module would also have been viewed as science fiction. Take a look at the following picture from that 1966 film classic:
The submarine with its passengers is in the middle left. The structure with the arms is a white blood cell. You can also see that WBC grabbing some blood-borne bacteria, probably bacillus subtilis, at the bottom. Yes, the submarine is next to be grabbed.
Is this really science fiction? How close are we to taking a ride in that mini-sub?
Well, we now have a small “bullet” about the size of a small bullet(!), that carries a camera. This bullet is ingested by a patient, travels through the digestive system, and takes photos as it travels. Better than a colonoscopy, yes? The camera is recovered via a bowel movement – it is then thoroughly cleaned (or it better be). Somebody with a very strange sense of humor (that would NOT be me) named this thing: The Mermaid. GASP! Here it is:
ow different is that from the science fiction submarine? Look at both and compare — scary, isn’t it?
OK – this happened about ten years ago. However, nothing like this had been done before that, and nothing of this nature has been done since. A stent was inserted into Grace Vanderwerken’s interatrial septum, because of anatomical issues she was having with her heart. So, what’s the big deal? The surgery was done while Grace was still an in utero fetus!!! Remember (from your Anatomy and Physiology class) the very interesting fetal heart? It has to be structured so that the lungs are bypassed, since the fetus is living underwater. The blood is therefore oxygenated via the placenta. Here is a picture you can use to brush up:
you can see that the interatrial septum is not complete. The opening in the wall is called the foramen ovale. When the lungs start to function, this closes. However, baby Grace had hypoplastic left heart syndrome. So, this would have placed undue stress on the lungs in the last few weeks of gestation. To overcome this, a stent was placed in that foramen, so that the placenta could continue oxygenation, and there would not be as much stress on the lungs. It worked.
Click on the following link to read all about it:
Grace’s in utero surgery
Talk about “Amazing Grace”………….