Transcript Scenario continued

Scenario
Paul is rushed into intensive care where a diagnosis of acute myocardial infarction (heart
attack) is made. His cholesterol level is 325mg%, and for a man of his age and lifestyle,
it should be well under 200mg%. Stacy calls the genetics center because Paul’s
cardiologist placed much emphasis on a review of Paul’s family history. He told Stacy
that “Paul’s case looks like the type that runs in families. It amounts to an inherited
tendency to early heart disease. By the way, how many children did you say you
have…?”
Scenario continued
The genetics staff explains that this type of familial
hypercholesterolemia (FH) is determined by a single, autosomal
dominant gene and that each of Paul’s children has a 50% chance of
having inherited the gene. Paul’s mother was revealed to have had a
coronary bypass at the age of 57. She is adopted and no further
information about her family is known.
Familial Hypercholesterolemia (FH)
• Cholesterol
levels
unregulated
– Builds up
• Gene on
chromosome
#19
• Potentially fatal
• Autosomal
dominant
Paul: Heterozygous for familial hypercholesterolemia
Stacy: Healthy
FH
FH
Key
F = FH disease
f = normal
normal
normal
Scenario
Paul’s condition stabilizes and long term dietary and drug treatment is planned. Paul is
depressed because he thought that his healthy lifestyle would have protected him
against such an event. The genetics staff explains that his lifestyle may have actually
postponed his heart attack or reduced its severity.
Plans are made to test other “at-risk” family members, in order to identify those who
have inherited the gene and who could benefit from aggressive management.
Scenario
Paul had a younger brother, John, who died several years ago at the age of 18 in a car
accident. He had fragile X syndrome, and was moderately retarded.
Fragile X
• Defected gene
on X
chromosome
– Recessive Xlinked
• Protein absent
• Mental
retardation
Scenario continued
Paul has a sister, Susan, who is 18 and another sister, Deborah, 19. Both are
offered lipid testing to determine if either has inherited the gene for FH. Susan
agrees to be tested and is found to have normal levels of lipids (fatty acid
substances, including cholesterol) in the blood. Years ago, when John was
diagnosed with Fragile X syndrome, she had her chromosomes tested to
determine if she might carry a gene for Fragile X. The chromosome study had
been normal.
Scenario continued
Deborah refuses testing. She has no faith in medical
science and relies instead on “folk medicines and certain
helpful visions”. Deborah had been offered Fragile X
chromosome testing when her brother was alive to see if
she might be a carrier. She had refused Fragile X testing at
that time as well. She believes that if her life is shortened by
heart disease, she will be “reincarnated as a Galapagos
turtle or something else that lives a long time, because
y’know, everything balances out. My brother Johnnie, he
had a rough life but I bet now he’s a lion or a dolphin or
something great like that.”
Plans are made to test
Stacy’s children. “Go
ahead and test Michelle
and Alan. I don’t think that
you need to test Frank.”
The genetics staff
reviewed the basics of
autosomal dominant
inheritance. “I understand
that. It’s just
that…well…there’s a good
chance that Paul isn’t
Frank’s father…”
Random practice problem
• Huntington’s disease is a dominant disorder found on
chromosome 4. Betty and Marcus met at a support clinic they
have been attending to help them cope with the knowledge of
their illness with Huntington’s disease. They would like to know
the risk of having a healthy child, now that Betty is pregnant.
Hh
Hh
Marcus
Betty
Key
disease
disease
H = Huntington’s disease
h = healthy
disease
healthy
?