Transcript Scene II: Will Alan ever play for the Lakers?

Scene II: Will Alan ever play for the
Lakers?
After this lesson, the students will be able to:
1) Explain x-linked inheritance using Factor VIII
deficiency (hemophilia) as an example;
2) Describe the treatment for hemophilia;
3) Explain the importance of early diagnosis and
carrier testing of hemophilia; and
4) Describe some societal issues associated with
hemophilia and its treatment.
Alan’s Situation
Alan suffers a painful knee
injury while shooting baskets
in his parents’ driveway.
Examination at the
emergency room indicates
that Alan has a bad sprain, in
addition to bleeding within the
knee joint. Further testing
reveals a deficiency of Factor
VIII, and a diagnosis of
classical hemophilia is made.
Stacy is found to have
reduced Factor VIII levels,
consistent with her being a
hemophilia carrier.
Alan’s Situation (contd.)
Following referral for genetic
counseling, Paul and Stacy
understand that the gene for
Factor VIII is on the Xchromosome. Since Stacy has
two X-chromosomes, only half
are unable to make usable Factor
VIII. The other half make all of the
clotting factor that she needs. But
Alan happened to inherit from her
the X-chromosome unable to
make Factor VIII. Because his
other sex chromosome is a Y, he
has no “back up” gene for Factor
VIII. Until his basketball accident,
the deficiency went unnoticed.
What is Hemophilia?
• Blood clotting disorder
usually affecting males
– 1 in 5,000
• Caused by abnormal
Factor VIII protein
– Factor VIII necessary
for blood clotting
– Clotting takes longer
• Inheritance pattern:
Sex-linked disorder (found
on X chromosome)
Sex Determination
• Sex determined by genes found on the X and Y
chromosome
• Females: egg produced with an X chromosome
• Males: ½ sperm cells contain X; and the other
½ contain Y
• There is a 50/50 chance of child being a boy/girl
Sex-Linked Disorders
• Defined: Recessive
inherited conditions linked
to the sex chromosomes
• Females: XX chromosomes
• Males: XY chromosomes
• More common in males
because only a single X
chromosome needs to be
damaged (both must be
damaged in females)
• Ex: Colorblindness,
Hemophilia, Muscular
dystrophy
Sample Colorblind Tests
Treatments
• Factor VIII Replacement:
– Injections of Factor VIII
protein
– Causes blood to clot when
injured
• Joint Replacement
– Knee, hip, ankle
replacement if arthritis is
severe
• Regular exercise for strong
muscles to protect the weak
joints
Alan’s Situation
Alan is starting on Factor VIII home infusion. His
parents are taught how to inject Alan with
Factor VIII that has been removed from pooled,
donated blood, purified and packaged for ready
use. The Factor VIII concentration can be kept
at home and prepared for injection only when
Alan feels that bleeding has occurred. The
concentration can also be taken with them on
trips.
Factor VIII Infusions
• Objective: replace missing clotting factor
• When used:
– Used at time of bleeding to prevent tissue
damage
– Prior to and during surgery
• Cost: over $100,000/year (beyond lifetime cost
of many insurance plans)
• Prior to 1984: HIV prevalent in the Hemophilia
community (70-90%)
Alan’s Situation
After the increased risk of hepatitis is discussed,
immunizations against Hepatitis B and D are
scheduled. Stacy is concerned about
hemophilia and AIDS. She is assured that while
AIDS was a threat to hemophiliacs receiving
pooled Factor VIII years ago, more strict donor
guidelines and heat-treating of pooled blood
reduces the chances of AIDS being a problem
for hemophiliacs. Stacy and Paul are
reassured. Yet Paul adds, “But let’s see if our
insurance will pay for the recombinant Factor
VIII.”
Alan’s Situation
Stacy recalls that about a year ago, a boy
in Frank’s school was discovered to be
HIV positive, presumably from
contaminated blood with which he was
transfused during heart surgery.
Several parents demanded that the boy
be removed from school, threatening to
remove their own children if their
demands were not met. Stacy
remembered following the issue in the
newspapers. She remembered that the
boy and his family moved out of state
before the school board or disgruntled
parents took any action. At the time,
she took no particular position on the
issue. What must it have been like for
the boy and his family?
Expanding the Chance Family
“Stacy, since hemophilia is X-linked and you’re a carrier,
it’s important that we contact other family members of
yours to discuss their risk of being carriers. Do you
have any sisters?” inquires the genetic counselor.
“Yes, one. And a brother, David.”
“Your sister might also be a carrier. You should bring her
up to date on this and ask her to make an appointment
with us.”
Stacy refuses. “And if you tell her anything about Alan’s
hemophilia, I’ll sue you and this place for everything
you’re worth.”
Practice: Jen is a healthy carrier of hemophilia
and Adam has no history in his family.
What is the probability of
getting:
Healthy
girl
Healthy/
carrier girl
Healthy
boy
Hemophilia
boy
Key
XD = healthy
Xd = disorder (hemophilia)
Daughter with hemophilia?
0%
Carrier child?
25%
Child with hemophilia?
25%
Two healthy children?
¾ x ¾ = 9/16 (56%)
Practice: Kelly is a healthy carrier of hemophilia,
but Jim suffers from the disease.
What is the probability of getting a:
Healthy son?
25%
Healthy/
carrier girl
Hemophilia
girl
Healthy daughter?
25%
Healthy
boy
Hemophilia
boy
Child with hemophilia?
50%
Key
XD = healthy
Xd = disorder (hemophilia)
Carrier child?
25%