phenylketonuria

PhenyiketonuriaMetabolic & Molecular Basis of Inherited Disease

A.N. Emami R.

Saturday, April 8, 2023 Total slide : 45 3


Case 1Patrick

Birth History: Full Term, 3,620 gmUncomplicated Pregnancy, Labor & DeliveryMother 24 yr old, healthyNo Prenatal exposure to alcohol, drugs, infection, known teratogensDischarged home on day of life 2



Case 1 (CONTINUED)

Developmental HxRolled over – 3 monthsSocial smile - 4 mStand alone – 14 mFirst word – 18 mPhrases – not yetWalk alone – 2 yr

Seizure HistoryFirst – 11 mGeneralized, tonic/clonicTotal – 4 seizuresMRI – decreased grey/white differentiation and cortical atrophy



Case 1 (Cont)

Physical ExamGrowthBlond hair, blue eyesNon-dysmorphic childNeurological exam:

Decreased tone, brisk reflexes



PatrickNormal• Abnormal high intensity signal in deep white matter• Leucodystrophy and Cortical atrophy

http://www.e-radiography.net/ibase5/1_Normal/slides/Brain_normal_brain_1_mri.jpg



Case 2

Jeremy newborn maleFull Term: 3,100 gmUncomplicated P,L & DNo perinatal infection, no alcohol, no drugs, no known teratogens

Mother - 19 yr oldFirst PregnancyFather -18 yr oldHealthy



Case 2Physical Exam and Labs

Ht & Wt = 70% General exam normalHC< 5% Neurological exam - normalUrine Ferric Chloride (FeCl3) is positive



Case 2

Jeremy is now 13 years old and exhibits

Persistent microcephalySpasticityMental retardation

Coarctation of Aorta



Case 3

Luis (8yo) referred to Developmental Pediatrics clinic

Chief Complaint: Hyperactivity and Learning Disabilities

Patient and his Brother•Self selects diet

•low in meat, eggs, cheese•enriched in fruits / vegetables

•Similar pigmentation to his brother



Case 4

Hannah: 6 month old female Diagnosed with metabolic disorder on abnormal newborn metabolic screenNormal growth / developmentNormal physical examOn treatment with metabolic formula



All four cases

Examples of hyperphenylalanemiaDefects in metabolism of phenylalaninePrototype – PKU

Elevation of PHE > 20 mg/dlNormal < 2 mg/dl



PKUClinical Findings

Mousy or musty odorExzemaFair coloring (decreased hair and skin

pigmentation)Behavior Problems

Mental RetardationLose ~ 1 IQ point per week of non-treatment



Phenylalanine Metabolism

PhenylalanineEssential AAMajor interconversions through tyrosine

PHE

TYRBody Protein

Melanin

DOPA

NE / EPI

Food Catabolism

50%



Conditionally Essential AA



Essential Amino Acids

HistidineIsoleucineLeucineLysineMethionine (and/or cysteine)Phenylalanine (and/or tyrosine)ThreonineTryptophanValine



Phenyl lactatePhenylacetatePhenylethylaminePhenylacetyl glutamine

Alternate Disposal Urine

Mousy or mustyodor



PKU

Autosomal Recessive disorder caused by mutation in PAH geneNewborn screening started in 1963Incidence: 1 in 15,000Subtypes and heterogeneity

ClassicModerate and mildNon-classical or non-PKU hyperphenylalaninemia



PKU


ClassicModerate and mildNon-classical or non-PKU hyperphenylalaninemia

% enzyme activity determines clinical severity



PKU


ClassicMildHyperphenylalaninemia

% enzyme activity determines clinical severity



PKU


ClassicModerateMildHyperphe

Tetrahydrobiopterin (BH4) responsive Hyperphenylalaninemia

• Urine pterins• blood dihydropteridine reductase



BH4 Responders

PAH mutation62% catalytic21% regulatory

Allelic pattern1 mild + 1 severe2 mild2 severe (rare)

Diet – BH4 without protein restriction



Biological Effects

HyperPhe inhibits transport of large, neutral AA into the brain (as does Leucine)

Inhibition of protein and neurotransmitters Deficiencies of dopamine, serotonin



Major Neuropathologic changes

1. Hypomyelination (Phe-sensitive oligodendrocytes)

2. White matter degeneration (leucodystrophy)3. Developmental delay/arrest cerebral cortex

Microcephaly Mental retardation Seizures



Non-Neuro pathology

Hypomelanosis – Why ?



Non-Neuro pathology

HypomelanosisBlond hair, blue eyes, pale Deficient Tyrosine production (precursor of Melanin)

CardiacCoarctation of the Aorta



Maternal PKU syndrome

First mentioned in literature in 1937First mentioned as a complication of PKU in 1956

Women with MR and PKU has 3 children, all retarded despite not having PKU

Microcephaly and cardiac defects reported in 1960’s1983 – MPKUCS begun



Maternal PKU Collaborative Study

Untreated women92% risk of mental retardation73% risk of microcephaly40% risk of low birth weight12% risk of congenital heart disease

Reduced risk if maternal plasma phe levels are normalized pre-conceptually




Dose-Response Relationship Goal: Phe level between 2-6 mg/dl by 8 weeks




The longer ittakes to get Phelevel < 8 mg/dlthe lower the IQof the baby



Balancing Metabolic Control

Exposure to normal

PHE intake

Elimination of PHE

from the diet




Exposure to normal PHE intake:Elevations of PHEElevations of PHE-ketonesDeficient TYR, DOPA, NE, EPIMental retardation / seizures




Exposure to normal PHE intake:Elevations of PHEElevations of PHE-ketonesDeficient TYR, DOPA, NE, EPIMental retardation / seizures

= Bad




Elimination of PHE from the diet:Decreases PHEDecreases PHE-ketonesDeficient TYR, DOPA, NE, EPIDEATH from essential AA deficiency




Elimination of PHE from the diet:Decreases PHEDecreases PHE-ketonesDeficient TYR, DOPA, NE, EPIDEATH from essential AA deficiency

= Bad



Optimal Therapy of PKU

Initiate treatment by 7 days of lifePhenylalanine levelsAge Level Freq of Testing

0-12 months 2-6 mg/dl 1x/week1-12 years Same 2x/month> 12 years 2-15 mg/dl 1x/month

Pregnancy 2-6 mg/dl* 2x/week



summery

HyperphenylalanemiaAn abnormal lab finding Several defects may result in hyperphe

Specific Dx is criticalPHE restriction in

BH4 deficiency is lethal

Treatment isEffective if begun early and continued for lifeAggressive management during growth and during illness



What about our cases??

Patrick – case 1 Dx ?

3 yr old with developmental delay and seizures…..

Jeremy – case 2 Dx ?• Newborn with

microcephaly and + FeCl3

• Now mentally retardedChoices1. Classic PKU – treated or untreated2. Maternal PKU3. Hyperphe



What about our cases??

Patrick – case 1 Classic PKU (mod)• 3 yr old with

developmental delay and seizures…..

• Patrick has permanent disabilities

Jeremy – case 2 Maternal PKU syndrome• Newborn with

microcephaly and + FeCl3• Now mentally retarded• He is metabolically

normal… but his mother had PKU

• His mother wants more children but is not on diet



Our Cases

Luis - Case 3Dx ? • 8yo with learning

disability and hyperactivity

Hannah - Case 4 Dx ?• 6 month old• Normal growth and

developmentChoices1. Classic PKU – treated or untreated2. Maternal PKU3. Hyperphe



Our Cases

Luis - Case 3 Classic PKU (Mexico)• On treatment• His hyperactivity has

improved• He will not regain

normal intellect

Hannah - Case 4 Classic PKU, treated• Continues to do well

on therapy• Growth, development

and intellectual situation are normal



The End

phenylketonuria

Education

total slide

metabolic formulatuesday

yr cortical atrophytuesday

yr olduncomplicated

month old femalediagnosed

decreased tone

jeremy newbornmother

iq point