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Scene 1: Michelle is saved by the starving bacteria

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

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Scene 1: Michelle is saved by the starving bacteria

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  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. 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. Michelle’s Situation

  3. 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. Mandatory PKU Testing

  4. 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? PKU Testing: Guthrie Test

  5. 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 What is PKU?

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

  7. 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 Treatments

  8. Normally, phenylalanine is converted into tyrosine and then into a protein Enzyme phenylalanine hydroxylase is absent/reduced Phenylalanine builds up in blood Chemistry of PKU

  9. Chances’ reaction Paul denies his contribution to his daughter's condition. He is a successful businessman, proud of his healthful lifestyle. He doesn't smoke, he jogs six miles a day and he enjoys a healthy diet. He attributes Michelle's condition to a "weakness on Stacy's side of the family" and refuses to believe that he has any "bad genes." The genetic counselor mentions that everyone carries an estimated 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.

  10. 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, "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." 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. 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, "Well I guess we won't be seeing you again for a long time." • Little does she know...

  11. 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

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