Topics in Genetic Counseling - PKU Educational Activity

Match the following basic facts about PKU from the presentation.

• type of inheritance

• Kuvan

• most PAH mutations are this type

• Autosomal recessive

• enzyme therapy derivative

• Palynziq

• reduces Phe levels in some patients

• 1:10,000

• incidence in US Caucasian population

• Missense

PKU testing is in the newborn screen in ? states

Which of the following is NOT a common symptom of patients with PKU?

• Intellectual disability 

• Musty body odor 

• Posture/gait abnormalities

• Eczema/light skin pigmentation

• Skeletal dysplasia

Answer explanation

Although osteopenia (failure to make new bone after absorption of old bone) is observed in PKU, skeletal dysplasia is not.

You have a confirmed positive result from an NBS for a PKU patient. The patient is a compound heterozygote (R408W // Y414C). What resource could you use to determine if Kuvan will work?

• New England Consortium

• National PKU Alliance

• BIOPKU

• PKU GOLIKE

• GeneReviews

Kuvan lowers the Phe levels by how much?

• 80-90%

• 3-5%

• 50-60%

• 20-30%

A family returns with a 3 day old baby boy after NBS came back positive for PKU. Neither parent has PKU. What do you counsel on first?

• Most NBS results are false positives so the overall risk is very low.

• Without a strong family history, the baby's risk is low but not possible to predict exactly.

• Based on the family history, there is at most a 33% recurrence rate for future pregnancies.

• After starting a low Phe diet, confirmatory biochemical/genetic testing is indicated.

Answer explanation

Despite high sensitivity/specificity, FP's on NBS do happen. Autosomal conditions like PKU have a 25% recurrence rate when both parents are carriers. Starting a low Phe diet while awaiting confirmation can get the baby started off on the right foot.

At which Phe blood level would a diagnosis of moderate PKU be made?

Answer explanation

The moderate form of PKU shows a consistent [Phe] serum level of 1200-900 micromolar. Classic PKU is above 1200 micromolar.

In a patient with classic PKU that is not adhering to any diet, which amino acid would you expect to see elevated levels of?

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Answer explanation

Tyrosine is the next step in the breakdown of phenylalanine and is important for making neurotransmitters in the body.

Select the 2 snacks in your pack that you would avoid putting in the lunch bag of a child with PKU?

Answer explanation

The Snickers bar and the Twizzlers both have higher levels of protein than the other snacks.