Download Genetic Disorders and Genetic Testing

Genetic Disorders and Genetic
Testing
Medical Interventions
© 2010 Project Lead The Way, Inc.
What are Genetic Disorders?
 Both environmental and genetic factors
play a role in the development of
disease.
 A genetic disorder is a disease caused
by abnormalities in an individual’s
genetic material.
 In this course, we will consider four different
types of genetic disorders:
 Single-gene
 Multifactorial
 Chromosomal
 Mitochondrial
Single Gene Disorders
Single gene disorders are caused by
changes or mutations that occur in the DNA
sequence of one gene.
Remember that a gene, a segment of DNA,
contains instructions for the production of a
protein.
Diseases and disorders result when a gene is
mutated resulting in a protein product that
can no longer carry out its normal job.
Single Gene Disorders
 Single gene disorders are inherited in recognizable
patterns:
 Autosomal dominant
 Autosomal recessive
 Sex linked
 Genetic testing looks at genotype to determine if
someone has a genetic disorder, will develop one, or
is a carrier.
Review Question
 A man and a woman are both carriers for sickle cell
disease, an autosomal recessive trait. What is the risk
of their having an affected child?
Answer
 Each parent is heterozygous for the
condition and has the genotype Ss
(where “s” is the recessive sickle cell
allele). Each parent passes one allele to
the child, so there is a 25% chance that
the child will have sickle cell disease.
 Think back to PBS – what is sickle cell
disease and what is life like for a person
affected with this disorder?
Multifactorial Disorders
 Multifactorial disorders are caused by
a combination of environmental
factors and mutations in multiple
genes.
 Development of heart disease is
associated with multiple genes, as well as
lifestyle and environmental factors.
 Different genes that influence breast
cancer development have been found
on chromosomes 6, 11, 13, 14, 15, 17 & 22.
 Many of the most common chronic
illnesses are multifactorial.
Chromosomal Disorders
Humans have 46 chromosomes in their body
cells.
44 autosomes
2 sex chromosomes
Because chromosomes carry genetic
information, problems arise when there are
missing or extra copies of genes, or breaks,
deletions or rejoinings of chromosomes.
Karyotypes, pictures of the paired
chromosomes of an individual, are
important in diagnosing chromosomal
disorders.
Karyotypes
Tour of Basic Genetics
http://learn.genetics.utah.edu/content/basics/
Mitochondrial Disorders
Mitochondria, the organelles in
your cells that convert energy,
also contain DNA.
A mitochondrial disorder, a
relatively rare type of genetic
disorder is caused by mutations in
nonchromosomal DNA of
mitochondria.
Mitochondiral DNA is unique in
that it is passed solely from
mother to child
Types of Genetic Testing
and Screening
Carrier Screening
 Carrier screening determines whether an individual carries a copy of
an altered gene for a particular recessive disease even though they
do not show the trait phenotypically.
 Carrier screening is often used if a particular disease is common in a
couple’s ethnic background or if there is a family history of the
disease.
 Examples of carrier tests include those for Tay-Sachs disease or sickle
cell disease.
Preimplantation Genetic
Diagnosis
(PGD)
 PGD is used following in vitro fertilization to
diagnose a genetic disease or condition before
the embryo is implanted in the uterus.
 A single cell is removed from an embryo and
examined for chromosome abnormalities or
genetic changes.
 Parents and doctors can then choose which
embryos to implant.
 Secrets of the Sequence – Chosen Child video
http://www.sosq.vcu.edu/videos.aspx. Type in
“Chosen Child” into Keyword search and view
the “Chosen Child – Screening Genetic
Content” video.
The Process of
Preimplantation
Genetic Diagnosis
Fetal Screening/Prenatal
Diagnosis
 Prenatal diagnosis allows parents to diagnose a
genetic condition in their developing fetus.
 Techniques such as amniocentesis, chorionic villi
sampling (CVS), and regular scheduled ultrasound
allow parents to monitor the health of the growing
fetus.
Newborn Screening
The most widespread type of genetic
screening, newborn screening is used to
detect genetic or metabolic conditions for
which early diagnosis and treatment are
available.
State tests for newborns typically screen
anywhere from 4 to over 30 genetic or
metabolic disorders.
Testing protocol and mandates vary from state
to state.
The goal of newborn screening is to identify
affected newborns quickly in order to
provide quick treatment and care.
Activity 2.1.1
 In this activity, you will assume the role of a genetic counselor and
meet with clients faced with difficult decisions regarding genetic
disorders and genetic testing.
 Your goal is to effectively explain the disease or disorder to your
clients as well as to outline potential options for genetic testing and
screening and overall management of disease.