1. The Story of Phenylketonuria and
the Path to Treatment
Stephanie Sacharow, MD
NERGN & Weitzman Institute
Genetics Webinar Series
2/8/2022

2. Learning Objectives:
1. Identify the milestones that lead to interest in intellectual
disability syndromes and the discovery of PKU
2. Understand how newborn screening began and evolved, and the
impact of newborn screening
3. Review the path to treatment and prevention of intellectual
disability in affected individuals
4. Discuss conventional dietary therapy and novel therapies for PKU,
as well as new treatments in clinical trials

3. Discovery of PKU

4. Discovery of PKU
•Dr. Asbjørn Følling: Norway, 1934
• Ferric chloride test
• Found phenylpyruvic acid in the
urine of siblings with intellectual
disability
Phenylalanine Tyrosine
Phenylpyruvic acid

5. Pearl S. Buck
•Nobel- and Pulitzer-prize winning novelist Pearl S.
Buck
•wrote about her own daughter, who was
disabled by PKU
Published
1950

6. Discovery of PKU
•Horst Bickel, German physician, working in
England on PhD in Biochemistry, 1951-2
• Implemented PKU diet – during his
Pediatric fellowship

7. President Kennedy meets with the McGrath Family

8. Summary of Clinical Features of Untreated
PKU
• Global developmental delay and variable intellectual
disability
• + Autistic features
• Epilepsy
• Musty odor
• Eczema
• Decreased skin and hair pigmentation
• Parkinson-like features (particularly in adults)
*All avoidable with treatment

9. Robert Guthrie
1958-1962

10. Newborn screening for PKU

11. Metabolic Conditions Tested by Recent NBS
Disorders of fatty acid oxidation
2,4-Dienoyl-CoA reductase deficiency
Carnitine acylcarnitine translocase deficiency
Carnitine palmitoyltransferase I deficiency
Carnitine palmitoyltransferase II deficiency
Carnitine transport defect
Electron transfer flavoprotein deficiency
ETF ubiquinone oxidoreductase deficiency
Long-chain L-3-OH acyl-CoA dehydrogenase def.
Medium-chain acyl-CoA dehydrogenase deficiency
Medium-chain L-3-OH acyl-CoA dehydrogenase def.
Medium chain ketoacyl-CoA thiolase deficiency
Short-chain acyl-CoA dehydrogenase deficiency
Trifunctional protein deficiency
Very long-chain acyl-CoA dehydrogenase def.
Disorders of amino acid metabolism
Arginase deficiency
Argininosuccinate lyase deficiency
Argininosuccinate synthase deficiency
Maple syrup urine disease (MSUD)
Citrin deficiency
Cystathionine -synthase deficiency
Methionine adenosyltransferase deficiency
Mitochondrial ornithine trasport defect (HHH)
Phenylalanine hydroxylase deficiency (PKU)
Defects of biopterin metabolism
Fumarylacetoacetase deficiency
Tyrosine aminotransferase deficiency
Disorders of organic acid metabolism
2-CH3 butyryl-CoA dehydrogenase deficiency
2-CH3 3-OH butyryl-CoA dehydrogenase deficiency
3-OH 3-CH3 glutaryl-CoA lyase deficiency
3-CH3 crotonyl-CoA carboxylase deficiency
3-CH3 glutaconyl-CoA hydratase deficiency
Isobutyryl-CoA dehydrogenase deficiency
Isovaleryl-CoA dehydrogenase deficiency
Glutaryl-CoA dehydrogenase deficiency
Malonyl-CoA carboxylase deficiency
Methylmalonyl-CoA mutase deficiency
Disorders of cobalamin metabolism
-ketothiolase deficiency
Multiple carboxylase deficiency
Propionyl-CoA carboxylase deficiency
Other enzyme disorders
Galactosemia
Biotinidase Deficiency
Pompe Disease (pilot)
Mucopolysaccharidosis Type I (Pilot)
X-linked Adrenoleukodystrophy (Pilot)
Collective incidence
1:2-4,000 newborns
Clinical impact (US):
Up to 2,000 cases/year

12. Overview of Phenylketonuria (PKU)
• Phenylalanine Hydroxylase (PAH) deficiency
• Autosomal recessive
• Elevated Phe  cognitive impairment and
neuropsychiatric symptoms
(https://southeastgenetics.org/userfiles/images/PKU%20pathway%20dianne%20-%20adria%20edit3%20-
without%20ohh20.png)

13. PKU Cofactor Disorders

14. Phe Neurotoxicity
• Factors related to toxicity
• Concentration of Phe
• Deficiency of other LNAA
• Untreated PKU 
• Altered white and gray matter
morphology
• Microcephaly
• Inhibited growth of the cortex
and disrupted myelination
A–C, FLAIR (A), trace diffusion-weighted
(B), and ADCav (C) images show extensive
white matter abnormalities with restricted
diffusion

15. Pathophysiology of PKU:
Summary of potential mechanisms of neurocognitive
impairment by high phenylalanine concentrations

16. PKU Treatments
• Dietary intervention
• Severe restriction of dietary Phe
• Phe-free amino acid–modified medical foods
(https://southeastgenetics.org/userfiles/images/PKU%20pathway%20dianne%20-%20adria%20edit3%20-
without%20ohh20.png)

17. PKU Diet
http://depts.washington.edu/pku/about/diet.html

18. Efficacy of PKU Diet
• Normal intellectual quotients (I.Q.)
• I.Q. gap when compared to their non-PKU siblings
• Lower scores for certain neuropsychological functions
• Executive function

19. PKU Treatments
•Cofactor therapy with sapropterin
(https://southeastgenetics.org/userfiles/images/PKU%20pathway%20dianne%20-%20adria%20edit3%20-
without%20ohh20.png)

20. Cofactor therapy - sapropterin dihydrochloride
• Approved by the FDA - December 2007
• Improves Phe tolerance in about 40% of PKU patients
• Milder genotype are associated with higher sapropterin responsiveness
• requires trial period to evaluate its effectiveness.

21. LAT-1 Transporter for LNAA
• Phe is transported into the brain by the L-amino acid
transporter 1 (LAT-1)
• The binding of a LNAA to a transporter is a competitive
process
• LAT-1 has the highest affinity for Phe
• Phe  disturbance in neurotransmitter production
Large Neutral Amino Acids

22. Glycomacropeptide
• Glycomacropeptide (GMP) is a whey-based protein that is
produced when making cheese.
• Dietary protein containing a minimal amount of Phe
• contains 2.5-5 mg Phe/g protein
• Alternative to the amino acid based medical foods
• Examples: BetterMilk, PhenylAde GMP

23. Phenylalanine ammonia lyase or “PAL”
• PAL (Phenylalanine ammonia lyase) is an
injectable plant, fungi, and bacterial
enzyme that breaks down Phe
• PAH (Phenylalanine Hydroxylase) is the enzyme
that is not working in PKU patients
• Enzyme substitution enzyme therapy for
PKU
• FDA-approved 2018
• Trademark as Palynziq (Pegvaliase)
Trans-cinnamic
acid
Phenylalanine

24. Pegvaliase
• Phenylalanine Ammonia Lyase (PAL) enzyme
• Recombinant Anabaena variabilis phenylalanine
ammonia lyase
• Pegylation
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phenylalanine-ammonia-lyase
rAV-PAL
Monomer
(MW 64,000)
Pegvaliase-pqpz
(rAV-PAL–PEG)
~150,000 atoms
(MW 1,200,000)
Longo N et al. Lancet. 2014;384:37-44. Image credit: Peerview.com

25. Outcomes Overview- PAL Clinic at BCH
• 45 active patients have been on PAL >1 year
• 44 show response to treatment
• Some have fluctuating response (e.g. 27 2.616mg/dl)
• Most on a regular diet
• Discontinuations for various reasons
• adverse events, anxiety, variable response
60 total patients treated (48
active)
37 drug-naïve
(8 discontinued
2 transferred in)
21 post-clinical
trial
(4 transferred out)
44/48 show response
to treatment

26. Results: Phe decrease over time
PRISM STUDY
• 261 participants
• Mean (SD) blood Phe
• 1232.7 (386.4) μmol/L at baseline
• 564.5 (531.2) μmol/L at 12 months
• 311.4 (427) μmol/L at 24 months
• Phe decreased from baseline - 51.1% and
68.7%, respectively
BCH PAL Clinic
• 20 study patients at close-out (~30 total)
• 24 naïve on treatment, 10 reached 12 months on
treatment
• Mean blood Phe
• 1146 μmol/L at baseline
• 534 μmol/L at 12 months
(for 10 patients who reached 12 months on treatment)
• 306 μmol/L at lowest point
• Phe decreased from baseline – 53%

28. Side-effects Data
• PRISM Study
• The most common AEs were:
• Arthralgia (70.5%)
• Injection-site reaction (62.1%)
• Injection-site erythema (47.9%)
• Headache (47.1%)
• BCH Population
• The most common AEs were:
• Injection-site reaction (includes
erythema) 23/26 (88%)
• Arthralgia 18/26 (69%)
• Rash 18/26 (69%)
• Fatigue 12/26 (46%)
• Headache 9/26 (35%)
• GI symptoms 7/26 (27%)
• Fever/Chills 6/26 (23%)
• Hair loss 5/26 (19%)
• Lymph nodes 4/26 (15%)
• Dizziness 2/26 (8%)
• STEROID needed 11/26 (42%)
*Auto-injectable epinephrine required due to risk of anaphylaxis

29. Future therapies
(in clinical trials)

30. Gene therapy: Genome editing

31. Gene therapy: Gene transfer
https://www.nhlbi.nih.gov/health-topics/genetic-therapies

32. Summary of therapeutic approaches for
phenylketonuria (PKU)
Metabolites 2014, 4, 1007-1017; doi:10.3390/metabo4041007

33. Acknowledgements
Harvey Levy Program for Phenylketonuria
and Related Conditions
Olaf Bodamer, MD, PhD, Associate Chief, Division of Genetics
and Genomics
Gerry Berry, MD, Director of the Metabolism Program
Harvey Levy, MD, Emeritus Director of the PKU Program
Susan Waisbren, PhD, Emeritus Co-Director of the PKU Program
Stephanie Sacharow, MD, Program Director
Boston Children’s PAL Clinic Team & Leadership
Stephanie Sacharow, MD, Medical Director
Ann Wessel, MS, RD, LDN
Leslie Martell, MS, RD, LDN
Suzanne Hollander, MS, RD, LDN
Krista Viau, PhD, RD, CSP
Amy Kritzer, MD
Benjamin Goodlett, PhD
Harvey Levy, MD
Fran Rohr, MD, RD, LDN