Tuesday, July 24, 2012

Genetics 102: Questions and Answers (Hopefully)

This are some more questions and answers, I decided to chop it into smaller bites since all this information can become a little overwhelming. (At least it felt that way for me.)
Also, if you're new to the whole thing, I did find from our experience that there are different types of genetic tests available, looking at different pieces of information, this are the ones that we had done:

1. FISH test: A preliminary test that looks into the most common pairs of chromosomes that present problems: 13, 18, 21, X,Y.
2. Amniocentesis: Test used to verify that there are indeed 23 pairs of chromosomes. 22 autosome pairs that are the same for males and females, and the 23rd pair which determines the sex. XX for female and XY for male.
3. Microarray: Zoomed in look at the chromosomes. Able to find more rare genetic conditions.
4. Whole Exome Sequencing: When all else fails and you still have no answers. Very expensive, not covered by private insurance yet. We didn't get to run this test for our boy.

Hope this preliminary info brings some background to the following questions:

1. What are the top 5 most common myths of genetics?

What a fun question! Off the top of my head, I'd say: 1. Genes can skip generations. 2. Having the same blood type as your spouse will cause birth defects 3. Scientists can know everything about you by looking at your DNA. 4. Red heads are going to go away due to evolution. 5. Genetic counselors will tell expectant parents whether or not to keep their baby.

Answer by: Diane Masser-Frye: I work at a Children's Hospital with families of children with genetic conditions. I also consult with an agency that provides services to people of all ages with developmental disabilities. My role is to help these individuals and families understand the role of genetics in their families and how their conditions are inherited.

2. I understand that the nucleus of the cell contains the DNA molecule. How do you jump from there to genes and chromosomes? 

Genes are contained within DNA. So, they are in the nucleus, too. Chromosomes are the forms that DNA take during certain times in the cell cycle.

Answer by: Kris Wetterstrand, M.S.: I work in the NHGRI Office of the Director as the Scientific Liaison to the Director for Extramural Activities. I have over ten years experience managing the NHGRI grant portfolio, having participated in the Large-scale Sequencing Program, which managed the Human Genome Project, and the Human Microbiome Project, an effort to sequence the DNA of microbes (e.g. bacteria) that live in and on humans and the ENCODE Project, an effort to identify functional DNA elements in the human genome. My background is in population genetics and molecular evolution.

3. Are all disorders developed because of problems with a person's chromosomes?

Not all disorders are because of chromosome problems. Some disorders are because there are too many or not enough copies of a whole chromosome, like Down syndrome. Some disorders are due to a change to a single gene located on a chromosome. But most diseases are complex, and have a number of factors that work together to cause the disease. Some of these factors are genetic, but many have to do with a person's environment and behaviors, like diet and exercise.

Answer by: Rachel Shapira: I am studying genetic counseling at the Johns Hopkins School of Public Health and the National Human Genome Research Institute. I am currently in a clinical rotation at the Walter Reed National Military Medical Center Prenatal Assessment Center.

4. What does the Microarray test looks into? Is it at specific genes? or chromosomes?

DNA microarrays can give us a "zoomed in" look at chromosomes allowing us to see genetic deletions or insertions that can't be seen just by looking at chromosomes under a microscope. The amount of information that can be obtained by a microarray varies depending on the type of array and some are capable of picking up very small deletions or insertions in the genome.

Answer by: Gillian Hooker, Ph.D., Sc.M.: I am the Associate Director of the Johns Hopkins Bloomberg School of Public Health/National Human Genome Research Institute Genetic Counseling Training Program and a contracted staff scientist within the Social and Behavioral Research Branch of the NHGRI. Prior to entering the field of genetic counseling, I completed my Ph.D. in Molecular, Cellular and Developmental Biology.

5. Does the Microarray test look into all the chromosome pairs?

It can. Scientists can set up a microarray to include all of a genome (all the chromosomes) or just parts of the genome (some of the chromosomes). It depends on what scientists interesting in studying.

Answer by: Kris Wetterstrand, M.S.: I work in the NHGRI Office of the Director as the Scientific Liaison to the Director for Extramural Activities. I have over ten years experience managing the NHGRI grant portfolio, having participated in the Large-scale Sequencing Program, which managed the Human Genome Project, and the Human Microbiome Project, an effort to sequence the DNA of microbes (e.g. bacteria) that live in and on humans and the ENCODE Project, an effort to identify functional DNA elements in the human genome. My background is in population genetics and molecular evolution.

6. Does a normal Microarray result mean that a person does not have a genetic syndrome?

Definitely not. A normal microarray result means there are no obvious (a few thousand bases or more) missing or deleted pieces of the genome. A person can have a genetic syndrome with just one single base substitution, which is not detected using microarray testing.


Answer by: Toni Pollin: I have a background in both genetic counseling and human genetics. I study the role of genetic factors in complex diseases, particularly diabetes and dyslipidemia, and the interaction of genetic with lifestyle and environmental factors. I also co-lead a human genetics PhD program and teach graduate, genetic counseling and medical students.

7. I know more and more about laboratories doing the whole exome sequencing. The question is, is there a benefit of sequencing the whole exome? Knowing that you might get a lot of variants of unknown significance. How do you report to the patient in that case? Sorry, we found something that we have no clue what it is, though you still have to pay thousands of dollars?

This is a fantastic question. Whole exome sequencing is new technology with great promise. We are still learning a lot about how to best use the information gained from exome sequencing to improve medical care. 

Many of the early patient exome sequences have been generated in hopes of identifying the genetic cause of a specific disease, to better guide treatment. Within these sequences, we are also finding variants which are already known to have important implications for other medical conditions in the patients and, potentially, in their family members. Over time, we expect to be better able to predict the significance of different variants, and have fewer "variants of uncertain significance."

Answer by: Gillian Hooker, Ph.D., Sc.M.: I am the Associate Director of the Johns Hopkins Bloomberg School of Public Health/National Human Genome Research Institute Genetic Counseling Training Program and a contracted staff scientist within the Social and Behavioral Research Branch of the NHGRI. Prior to entering the field of genetic counseling, I completed my Ph.D. in Molecular, Cellular and Developmental Biology.

8. How is a gene actually identified within a DNA sequence? is it by matching the entire sequence against it's expected pattern? Or is it also required to be located at a specific position within the sequence?

Genes are identified by matching the DNA sequence against its expected pattern, which means the pattern as well as the specific position within the sequence match.

Answer by: Dana Petry: I am a second-year genetic counseling student in the Johns Hopkins University/NHGRI Genetic Counseling Training Program. I am taking classes in genetics, public health, and psychosocial counseling. I have also rotated through various clinics for prenatal, pediatric, and cancer genetic counseling.

 8. What is the difference between the incidence of something and the prevalence of something?

Excellent point to clarify, as these are often used interchangeably. Incidence tells us about a change in status from non-disease to disease, thus being limited to new cases. Prevalence includes both new cases and those who contracted the disease in the past and are still surviving. In genetics, we usually discuss incidence as the birth rate for a given condition (1 in 50,000 births, for example) and prevalence for the number of affected individuals in a given region (US vs world, for example). 

Answer by: Julie Rousseau: Following many years in clinical genetic counseling, the majority of which was spent in pediatric genetics, I currently work in a laboratory setting. In this position, I interpret DNA results and help providers determine which test(s) are most appropriate for their patients.

More Q&A to come,


















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