Genetic Testing

Ronnee Yashon, Michael Cummings

• Publisher: Momentum Press
• Year: 2018
• ISBN:
  9781946646538
• Topic: Biological Sciences
• Subtopic: Genetics & Genomics
• Index: Biological Sciences

It is hard to avoid hearing about genetic testing. It is advertised, discussed, debated, and offered to patients. Some are over the counter, such as paternity testing, testing for risk for diabetes and others. Others are offered by private companies and still others by drug companies, These tests may or may not show a distinct answer, so it important for patients to understand these results. Early in 1920s a Eugenics movement began in the United States, courts decided which person had undesirable traits and would be sterilized so they could not pass these traits to their children. The idea here was to create a population with better genes (therefore healthier and richer). Families who were chosen received awards and people began to see the importance of genetics. But little did they know how it would EXPLODE! This book will look at genetic testing as it applies today and how the serious decisions that it demands, cannot be ignored.

CHAPTER 1

Introduction

Questions are scattered throughout this chapter and the following chapters. Watch for them and think about how they may apply to you and other ones.

Genetic disease is caused by a number of things. Before we knew about cancer being caused partially by environmental factors, we thought many things caused cancer. Genes in cancer cell cause them to multiply many times over forming a tumor. How do these genes change to cause cells to divide uncontrollably?

Mutations are changes in the DNA that can alter the proteins it codes for and, therefore, cause disease depending on what gene is active. Once the gene is located, the normal sequences can be disrupted in a number of ways (see Table 1.1).

Reproductive cells have ½ the number of chromosomes. And are made by the ovaries and testes and undergo a process called meiosis leaving the sperm and egg with ½ number of chromosomes (23). When fertilization occurs the nucleus of the egg and the head of the sperm create a body cell with 46 chromosomes.

Table 1.1 What changes DNA

At meiosis	During meiosis the chromosomes can break By external change Free radicals attach to the DNA (epigenetics) External exposure when in the mother uterus Disrupting the sequences that turn the gene on or off Inherit a mutation from a parent
Outside influences	As we all know things that mother injests or breathes in can be harmful to the fetus
When genes are turned on and off	Epigenetics examines what happens within the mother between conception and birth. Free radicals can make changes by holding the DNA

If, however, a mutation occurred or a mistake in meiosis happens, that it would be passed on to future generations.

Most inherited conditions are placed into one of three categories according to how the mechanism of the inheritance of the specific gene works. They are dominant, recessive, and sex-linked traits. See Table 1.2.

Table 1.2 Three examples of inheritance type

Huntington	Dominant	A child with a parent with HD has a 50% chance of inheriting the gene and therefore the condition
Sickle cell anemia	Recessive	If both parents have the gene, there is a 25% chance that the fetus will get both
Color blindness	Sex linked	The gene for color blindness is on the X chromosome and two genes are needed to show the condition, a male can only have one (and therefore has normal vision)

CHAPTER 2

Prenatal Testing

Major case: After a few months, X and Y become pregnant and they want to know more about their growing fetus. Not just the sex of their baby, quite a bit more of other information. Certain tests are recommended and a genetic counselor may work with the family.

Not so many years ago, when a woman got pregnant she could only guess the sex of her fetus and it was a real surprise to find out on the delivery table.

The first view into the uterus came with the invention of ultrasound. It was modeled after Sonar that was used to identify submarines while they were submerged. This makes sense if we remember the fetus is immersed in amniotic fluid. Without any harm to the fetus or mother, sound waves show a picture in a monitor. The figure below (Figure 2.1) shows a normal fetus at 18 weeks.

Figure 2.1 Drawing of fetus in uterus
(1) placenta; (2) umbilcal cord; (3) amniotic fluid; (4) uterus

At first only the sex, head size, and growth of arms and legs were discernable. Later when the ultrasounds became more sensitive, the heart, lungs, and other internal organs could be seen.

If you are wondering how ultrasound (sonogram) works, it is fairly simple. Sound waves are sent through the mother’s abdomen which includes the uterus and the fetus, and surrounding tissue. Then electronic waves are sent back to a screen and a good picture can be seen by the mother and physician.

A number of things can be diagnosed by ultrasound before the fetus is delivered. The obvious would be heart malfunctions (you can see the tiny heart beat), brain size, size of arms and legs, and other physical abnormalities.

Here is where problems can occur. Many ultrasounds are read by doctors with no training in this field. As you can see (Figure 2.2) much of the negative is blurry and difficult to read. Also, if abnormalities are found, the doctor is required to tell the woman what they are and discuss options. At this point it is necessary to clearly explain problems and solutions.

Figure 2.2 Ultrasound of fetus’s head
This ultrasound is taken from the top of the skull. The bright white circle is the skull. This type of view is used to determine if the brain is growing correctly

Note: This an ultrasound.

This situation involves one of the most difficult decisions a mother can make. Obviously one option is abortion, and another is to keep the baby and raise it or put the child up for adoption. It would depend on what the mother would want (see Roe v. Wade in Chapter 8).

I am not forgetting the father’s opinion, but in almost all of the states, laws give a pregnant woman, no matter what her age, the ability to make her own medical decisions. The rationale is that the fetus is in her body and therefore part of it.

In addition, some problems found in ultrasounds can be treated while the fetus is still in the uterus and some surgical procedures can correct spina bifida, hydrocephalus, and others. We have ...

Table of contents

• Cover
• Half-title Page
• Title Page
• Copyright
• Contents
• The Basics
• Chapter 1 Introduction
• Chapter 2 Prenatal Testing
• Chapter 3 Adult Testing
• Chapter 4 Screening
• Chapter 5 Ancestry DNA
• Chapter 6 Other Tests
• Chapter 7 Laboratory Methods
• Chapter 8 Landmark Legal Cases
• Chapter 9 Other Interesting Cases
• Chapter 10 Some Interesting Problems
• Epilogue
• Appendix A
• Decision Making Model
• References
• Index
• Backcover