2. What will you learn?
At the end of this presentation, you’ll be able to:
•Explain some basic concepts in genetics.
•Give three reasons patients are referred for pediatric
genetic evaluation and counseling.
•Describe the value of genetic counseling and testing.
•Describe four categories of genetic tests.
•Understand test results.
•Explain the work of the pediatric genetic team.
•Describe what a family can expect in a pediatric genetics
evaluation and counseling session.
2
4. What is “genetics”?
Genetics is the field of science and medicine that
studies the biological basis of heredity (how traits are
passed from one generation to the next) and how these
instructions for life are used by all living organisms.
4
7. How is genetic information passed on?
7
Humans have 23 pairs of
chromosomes in every cell.
The egg and sperm are
special; they have only one of
each chromosome.
When an egg and sperm come
together, they typically grow
into a child who has two of
each chromosome: one from
Mom, and one from Dad.
http://www.daviddarling.info/childrens_encyclopedia/Genetic_Engineering_Chapter1.html
10. 10
Original sentence
MOVE TO THE LEFT.
Gene Change
MOV
LE TO THE LEFT. MOLE TO THE LEFT.
Gene Reversal
MOVE TO THE LEFT. MOVE TO THE ELFT.
Gene Insertion
MOVIE TO THE LEFT. MOVIE TO THE LEFT.
Gene Deletion
MOVE TO THE LEFT. MOVE TO THEFT.
12. Types of changes
12
1. Inherited genetic changes
(“Your grandpa was just the same.”)
2. De novo genetic changes
(“Now, where did that come from?”)
3. Somatic genetic changes
(“I told you to stay out of the sun!”)
13. 13
But some are
CLINICALLY SIGNIFICANT
(they cause a problem)
Some changes are
BENIGN
(they cause no harm).
So what?
14. Pop Quiz
• What is the function of DNA in our bodies?
• What is a chromosome? What is a gene?
• How many chromosomes does a person typically
have?
• What is a genetic change at the chromosomal
level called?
• What is a genetic change at the gene level called?
• What does it mean if a change is “benign”? How
about “deleterious?” And “pathogenic?”
14
Editor's Notes
Show this slide as participants enter and are seated, and as you do your introduction and review logistics.
There is probably no field of medicine that is growing more quickly than genetics. New breakthroughs in gene mapping and advances in gene splicing technologies are bringing a revolution in how we predict, identify and treat many diseases, even those that up until now have been untreatable. It’s a very exciting time for providers and patients – and also for us interpreters who have to be able to interpret for these appointments!
This course is the second in a trilogy of Interpreting in Genetics courses funded by the American College of Medical Genetics and Genomics with support from HRSA. And this one focuses on interpreting in pediatric genetics. (click)
So, what are we going to learn in this course? Well, this is what we’re aiming for. (click)
At the end of this presentation, you will be able to:(click)
Explain some basic concepts in genetics. (click)
Give three reasons patients are referred for pediatric genetic evaluation and counseling. (click)
Describe the value of genetic counseling and testing. (click)
Describe four categories of genetic tests. (click)
Understand test results. (click)
Explain the work of the pediatric genetic team. (click)
Describe what a family can expect in a pediatric genetics evaluation and counseling session. (click)
So, what is “genetics” anyway? When you hear the word "genetics" what comes to mind? If you can say one or two words you associate with genetics, what would they be? (Elicit a few comments.) (click)
One definition says that genetics is the field of science and medicine that studies the biologic basis of heredity – or rather, how traits are passed from one generation to another -- and how the instructions for life are used by all living organisms. (click)
Let’s start at the cellular level. Basically, cells are the building blocks that make up our bodies, and different cells have different functions. A nerve cell is a little different from a muscle cell, which is different from a white blood cell, for example. But inside every cell are the structures that allow it to process energy, to reproduce, to get rid of waste, and to fulfill its particular function.
But how does the cell know what its particular function is? Whether it’s supposed to be a nerve or a muscle or part of the blood? And how do cells know how to work together? These instructions are all programmed into the cell’s DNA. (click)
Every cell in your body (with the exception of red blood cells) carries in its nucleus your DNA. DNA can be thought of as the instructions that the cells in our bodies use to grow, develop and function.
DNA in the nucleus is all packed tightly into units called chromosomes. If you could stretch out the DNA of a chromosome and look at it through a microscope, it would look like a long ladder that is twisted into a spiral. You may hear this spiral shape referred to as a ‘double helix.’ The rungs are various combinations of four nucleotides called Adenine, Thymine, Cytosine, and Guanine. These are often referred to as A, T, C, and G for short, and these letters spell out the genetic code.
Individual sections of DNA that code for a specific trait or function are called “genes”. So this section here might be the gene that codes for “Brown Hair” and the next section might be a gene that contributes to “Blue Eyes.”
The complete DNA structure, or genome, for a human contains about 3 billion “letters” and about 20,000 genes. These genes make up 23 pairs of chromosomes. (click)
We each receive half our DNA from our mother and half from our father. Here’s how it works.
(click) In each cell, we have 23 pairs of chromosomes. (click) The egg and the sperm are special. Instead of having a pair (that is, two) of each chromosome, they have only one of each chromosome. (click) When the sperm fertilizes the egg, each chromosome from the father joins the matching chromosome from the mother, and now the fertilized egg has, again 46 chromosomes – 23 pairs. (click)
That fertilized egg has the potential to become a full human being. How does that happen? Well, that one cell copies itself, just like in the picture here, to become two cells. Then it does that again, and again and again. And every time that one cell replicates, it typically makes an exact copy of the entire genetic code on those 23 pairs of chromosomes, so the new cell should have the exact same genetic make-up as the original cell. (click)
Sometimes, though, when the genetic code is being copied to make a new cell, (click) a mistake happens. When it happens down at the level of the genes, it is called a mutation or variant. When the mistake happens at the chromosomal level, it is called a chromosome abnormality. (click)
So, let’s start with genes. A gene can be thought of as a long string of letters that determine a particular trait – like hair color - or that tell the cell to perform a certain function. And when the cell reproduces, the DNA reproduces too, so the new cell has exactly the same genes as the original.
A variant can be thought of as a difference in the sequence of “letters” from what is found in the genetic code of the majority of people. This can happen in many ways. (click) A single letter can be changed, (click) there can be a mix up to the order of the letters, (click) some letters can be added or (click) letters can be deleted. Change in the “letters” of a gene change the instructions the gene carries, just as these changes in the letter order change the meaning of the sentence.
Locating a gene variant is sort of like finding a typo on one page of thick book. It’s hard to find unless you know exactly where to look. (click)
If a gene is like a series of letters that code for a particular word, then a chromosome is sort of like a whole chapter in the book. Just as we can have letters in a word that are changed, added or deleted, altering the word’s meaning, we can also have changes to entire chromosomes. The amount of genetic material we have is very important – that we have 23 pairs of chromosomes, with half from each parent, and with nothing extra or missing. Sometimes, (click) an extra chromosome can be present, or a chromosome can be missing. Or both of a pair of chromosomes can come from only one parent, with none from the other. Or a fragment of a chromosome can be duplicated or extra or deleted. (click)
These changes in the chromosomes and genes fall into three categories.
Some changes are (click) inherited. Let’s say that a woman has a gene mutation associated with breast cancer. That mutation exists in all of her cells, including her ova. If an ovum with the gene mutation for breast cancer is fertilized by a sperm, the resulting embryo will also carry this gene mutation.
Other changes are called (click) “de novo” genetic changes. As the Latin translation of the name suggests, these are “new” genetic changes. For example, a woman might have the normal number of chromosomes -- 46. But then one of her ova is fertilized, and when the cell starts to multiply, perhaps a “mistake” happens, causing the fetus to have cells with 47 chromosomes, or only 45. This is a “de novo” anomaly.
Finally, some changes are acquired during a person’s lifetime. These are called (click) “somatic genetic changes.” For example, exposure to UV rays from the sun can cause two letter “T”s in a gene to fuse together. Then when the gene copies itself, this leads to a mistake in the genetic code. (click)
But, so what? What happens if a little “typo” gets introduced into the genetic code? Or an additional “chapter” gets added to the “book”?
Well, sometimes, (click) nothing. These types of changes are called “benign variants,” which just means that they do not cause harm.
But others are (click) clinically significant – that means that they cause a medical condition. Genetic professionals refer to these changes as “deleterious” or “pathogenic variants.” Just as a change in the letters can mess up a word, changing the meaning of a sentence, genetic changes have the potential to disrupt the function of the gene, causing it to work differently. In the previous example with the sun fusing two “Ts together, it turns out that those “Ts” are supposed to limit cell reproduction. When those “Ts” don’t work right, the cell starts to reproduce without control. And what do we call uncontrolled cell reproduction? Right – cancer. This is why too much exposure to the UV light in sunshine can cause skin cancer.
An entire additional chromosome (which can contain thousands of genes), or the lack of one, can also change how the body develops and functions. And that can be a problem. This is why people are interested in knowing if these genetic changes are present.
So let’s pause here for a short quiz. (click)
Pop quiz! (click)
What is the function of DNA in our bodies? DNA serves as the “instruction book” that tells each cell how to grow, reproduce, die and fulfill its individual function. (click)
What is a chromosome? One of 46 structures in the cell nucleus that are made up of the DNA. (click)
What is a gene? A segment on the chromosome that codes for a particular trait or function. (click)
How many chromosomes does a human being typical have? 46, in 23 pairs. (click)
What is a genetic change at the chromosomal level called? A chromosome abnormality. (click)
What is a genetic change at the gene level called? A gene variant or mutation. (click)
What does it mean if a change is “benign”? Not harmful.
What does it mean if a change is “deleterious?” Disease causing.
How about “pathogenic?” Also disease causing. (click)
