1. Scene 1: Michelle is saved by the starving bacteria
After this lesson, the student will be able to:
explain recessive inheritance using phenylketonuria (PKU) as an example;
describe the Guthrie test for screening newborn babies for PKU
explain how PKU can be treated by a special diet and how this could postpone the effects of PKU until the next generation
discuss some of the economic issues associated with screening for the treatment of genetic conditions
explain why females with PKU need to be followed very closely in their reproductive years to avoid the problems associated with maternal PKU.

2. Michelle’s Situation
Stacy and Paul Chance are referred to the genetics center because their newborn daughter, Michelle, had elevated phenylalanine levels as determined by newborn screening. The diagnosis of phenylketonuria (PKU) is made.

4. Mandatory PKU Testing
The couple wonders why their child was tested. They have two other children, Alan (age 6) and Frank (12) who are apparently healthy, active, intelligent boys. The couple couldn't remember any special testing that either boy had at birth. State mandated newborn screening is explained to them. A description of PKU and its inheritance is provided, and dietary management is discussed.

5. PKU Testing: Guthrie Test
Mandatory statewide testing around day 2 ($5/child)
Bacteria grows on blood sample if excess phenylalanine is present
Treatment begins immediately
Why is $5/child more cost effective for the state then no testing at all?

6. What is PKU? PHENYLKETONURIA (PKU)
PAH gene on long arm of chromosome 12 is absent/reduced
Excess phenylalanine interferes with brain development
Autosomal recessive disorder
1:10,000-15,000 births
Effects: retardation, seizures, destructive, restlessness

7. Prognosis With treatment: Normal development
With minimal treatment: Intellectual defects
Without treatment: Retardation

8. Treatments Low phenylalanine diet
Baby fed special formula (~$10,000/year)
Vegetables and low phenylalanine foods added later in development
Regular blood samples taken and phenylalanine diet adjusted as needed
Eventually, a normal diet can be obtained

9. Chemistry of PKU
Phenylalanine hydroxylase
(enzyme)
Phenylalanine
(amino acid)
Tyrosine
(amino acid)
Melanin
(protein)
Normally, phenylalanine is converted into tyrosine and then into a protein
The Problem: Enzyme phenylalanine hydroxylase is absent/reduced
The result: Phenylalanine builds up in blood

10. Chances’ reaction
Michelle’s problem must be due to a weakness of Stacy’s side of the family. I don’t have any “bad genes.”
It’s not my fault Michelle is sick. I’m a successful business man. I don’t smoke. I jog 6 miles a day. I have a healthy diet.
Everyone carries 6-10 "unusual" recessive genes which cause no clinical problems in the carriers, but if two carriers of the same unusual recessive gene were to have children together, each child would have a 1 in 4 chance of inheriting the recessive condition for which the genes were responsible.

11. “but if two carriers of the same unusual recessive gene were to have children together, each child would have a 1 in 4 chance of inheriting the recessive condition”
Stacy H h
HH (healthy) Hh
(healthy) H
Key
H = Healthy
h = PKU disease
Paul Hh
(healthy) hh hh
(PKU disease) h

12. Genetic Counseling
Paul is relieved to know that being a carrier neither reflects negatively on his manhood nor does it isolate him from his peers. He quickly turns the situation to his advantage and states,
Stacy does not try to defend herself against Paul's earlier accusations but is relieved at his acceptance of the cause of Michelle's condition.
Well, if we're all carriers of some bad genes, I guess I'm better off than most of you. At least I know what one of my unusual genes is.

13. Genetic Counseling
The further complication of maternal PKU is mentioned. Paul and Stacy are scheduled to meet with a nutritionist, and follow-up appointments for monitoring blood phenylalanine levels are made.
Upon leaving, Stacy thanks the genetics staff and says,
Little does she know...
Well I guess we won't be seeing you again for a long time.

14. Essay Topic #1
Assume that you are Stacy or Paul Chance. Describe in writing your feelings after your visit to the genetics center.
Essay Format:
Ink or typed (no pencil)
Add title and date
Minimal length = ¾ page
If typed: 1” margins, 12-point times new roman font, double spaced.
Complete essays (Introduction, body, conclusion)
Spellcheck and proofread