Genetic Disorders and Genetic Testing

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Genetic Disorders and Genetic Testing
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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 individuals genetic
  material.
• In this course, we will consider four different
  types of genetic disorders
• Single-gene
• Multifactorial
• Chromosomal
• Mitochondrial

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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.

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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.

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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?

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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?

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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.

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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.

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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

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Types of Genetic Testing and Screening
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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 couples 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.

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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.pubinfo.vcu.edu/secretsofthesequence/pl
  aylist_frame.asp

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The Process of Preimplantation Genetic Diagnosis
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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.

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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.

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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.