The Story of Phenylketonuria and the Path to Treatment
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This document summarizes the history and treatment of phenylketonuria (PKU). It describes the discovery of PKU in the 1930s and milestones that led to newborn screening starting in the 1960s. Untreated PKU causes intellectual disability, but treatment involving a phenylalanine-restricted diet or medications can prevent disability. Current treatments include dietary therapy, cofactor therapy with sapropterin, and enzyme therapy with phenylalanine ammonia lyase. Gene therapy is also being explored. Newborn screening programs have helped identify thousands of cases annually to facilitate early treatment and prevention of intellectual disability.
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The Story of Phenylketonuria and the Path to Treatment
- 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
- 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
- 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)
- 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)
- 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 2.616mg/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
Editor's Notes
- http://npkua.org/Education/PKUandtheBrain.aspx