Types ,diagnosis & treatment

1. PHENYLKETONURIA
By :
NATHIYA

2. Case report :
 Summary :
A.R. is a six year old Malay boy was referred
to Hospital with the problem of aggressive behaviour
and developmental delay. He was born in Mecca,
Saudi Arabia after an uneventful pregnancy.
His mother noticed at the age of three months
that her child was rather quiet and could not hold his
head up. He rolled over at eight months, sat without
support at twenty months, walked at two years and
talked with meaning at three years of age.

3.  At about one year old the mother noticed that
his normal black hair gradually changed to light
brown.
There was no history of light hair on both
parental sides. The child also had no history of
fits or skin rashes.
The parents were first cousins and one of the
maternal grandfathers was mentally retarded.

4. WHAT PKU IS ?
Phenylketonuria is an autosomal recessive disorder
caused by mutations in the phenylalanine hydroxylase
(PAH) gene.
It results in the accumulation of phenylalanine (Phe),
an essential amino acid mainly metabolized in the liver
by the phe hydroxylase (PAH) system.
This enzyme hydroxylates Phe to tyrosine requiring
tetrahydrobiopterin (BH4) as a co-factor.
 Defects in either PAH or the production or recycling of
BH4 may result in hyperphenilalaninemia which can
cause intellectual disability if untreated.

5. Clinical examination :
 A stunted child with height and weight below the 3rd
centile and with light brown hair.
 He was very playful, hyperactive and shouted whenever
he wanted something.
 He was very destructive and aggressive towards other
children.
 He could not follow simple instructions and was unable
to read, write alphabetical letters or even perform simple
arithmatics.
 The gross motor development was normal.
 His mental age was assessed to be below 3.5 years old.
Apart from mental retardation the neurological
examination was normal.

6. Investigations :
 normal blood counts, blood glucose and electrolytes.
 Urine ferric chloride test was positive .
 Dinitro-phenyl hydrazine test (ANPH) was also positive.
 Plasma amino-acid chromatography revealed the
phenylalanine band was increased.
 The other siblings and the parents were screened but did
not reveal- any abnormality: EEG and computerised
tomography of the brain were normal.

7. The PAH gene is located on chromosome 12 in the band
12q22-12q24.2 . More than 400 disease-causing
mutations have been found in the PAH gene. This is an
example of allelic genetic heterogeneity.

8. # Mutations in PAH gene mostly result from
an arginine111 to tyrosine111 in exon3 point
mutation of the PAH gene.

11. PKU AFFECTED INFANTS :

13. Classic PKU (PHE LEVELS : >20mg/dl)
Classical PKU, and its less severe forms "mild PKU" and
"mild hyperphenylalaninemia" are caused by a mutated
gene for the enzyme phenylalanine hydroxylase (PAH),
which converts the amino acid phenylalanine to
tyrosine.
Tyrosine is necessary for the production of
neurotransmitters like epinephrine, norepinephrine, and
dopamine.
PKU may resemble amyloid diseases, such as
Alzheimer's disease and Parkinson's disease, due to the
formation of toxic amyloid-like assemblies of
phenylalanine.

14. White matter
abnormalities:
A decrease in
myelination levels of
extrapyramidal neurons
and glial cells where this
reduction is caused by
the transformation
of oligodendrocytes to
non-myelinating
phenotypes. This loss of
white matter is more
visible in periventricular
regions and the forceps
major and minor of the
corpus callosum in
cortex.

15. Gray matter abnormalities :
gray matter loss is most
prominent in motor and pre-
motor cortex, thalamus and
the hippocampus.
Interestingly, in certain
studies, an increase in gray
matter volume is observed in
ventral regions of striatum.

16. Atypical
Phenylketonuria: Tetrahydrobiopterin-deficient
hyperphenylalaninemia
 A rarer form of hyperphenylalaninemia.
 Occurs when the PAH enzyme is normal, and a defect is found in
the biosynthesis or recycling of the cofactor tetrahydrobiopterin .
 BH4 is necessary for proper activity of the enzyme PAH, and
this coenzyme can be supplemented as treatment.
 Tetrahydrobiopterin is a cofactor in the production of L-DOPA from
tyrosine and 5-hydroxy-L-tryptophan from tryptophan, which
must be supplemented as treatment in addition to the
supplements for classical PKU.

17. Genetic defects:
Tetrahydrobiopterin deficiency can be caused
by defects in four genes.
 They are known as HPABH4A, HPABH4B,
HPABH4C, and HPABH4D.

18. Maternal PKU:
 It was discovered that almost all offspring of women
with PKU not treatement are clinically abnormal (
delayed development , microcephaly , growth imparment
).
 As predicted by mendelian inheritance all children are
heterozygotes.
 Therefore their neurological development delay is not
due to their genetic constitution but due to
highly teratogenic effect of elevated effect of
phenylalanine in the maternal circulation .
 Accordingly, a women with PKU who Is planing
pregnancies commence a low – phenylalanine diet
before and throughout her pregnancy.

19. SYMPTOMS:
 seizures,
 hypopigmentation (excessively fair hair and skin), and
 a "musty odor" to the baby's sweat and urine (due
to phenylacetate, a carboxylic acid produced by the oxidation
of phenylketone) , pale hair and skin.
 If untreated,
Children often fail to attain early developmental milestones,
develop microcephaly, and demonstrate progressive impairment of
cerebral function. Hyperactivity and severe learning disabilities are
major clinical problems .
A characteristic "musty or mousy" odor on the skin, as well as a
predisposition for eczema.
The damage done to the brain if PKU is untreated during the
first months of life is not reversible.

20. Diagnosis:
1.Classic PKU :
The method of choice is TANDEM MASS
SPECTROMETRY (MS/MS) identifies with low – false
positive rate , excellent accuracy and precision .
 dietary phe deficiency can be manifested by
lethargy, failure to thrive , anorexia , anemia ,
rashes , diarrhea and even death.
 normal plasma phe levels : neonates (under 12yrs ) -
b/w 2-6 mg/dl.
Older individuals - b/w 2-10mg/dl.

21. 2. hyperphenylalanemia due to
deficiency of BH4:
• Hyper salivation
• Measurement of neopterin and biopterin in
body fluids especially in urine.
1. CSF examination-analysing the
decresed levels of dopamine,seratonin &
their metabolities.
2. BH4 loading test
3. Enzyme assay – DHPR measurement in
dry blood spots.

22. Are there any prenatal test for pku?
 Chorionic villus
sampling (CVS) is a
prenatal test that is used
to detect birth defects,
genetic diseases, and
other problems during
pregnancy.
 During the test, a
small sample of cells
(called chorionic villi) is
taken from the placenta
where it attaches to the
wall of the uterus.

23. Newborn screening:
Newborn screening is
the process of testing
newborn babies for
some serious, but
treatable, conditions.
 NBS can include a
heel stick, hearing
screen, and pulse
oximetry.

24. Medication for pku :
The U.S. Food and Drug Administration (FDA)
has approved the drug sapropterin
dihydrochloride (Kuvan®) for the treatment of
PKU.
Kuvan® is a form of BH4, which is a substance
in the body that helps break down
phenylalanine.
 Even if the medication helps, it will not
decrease the phenylalanine to the desired
amount and must be used together with the
PKU diet.

25. Life long supplementation with neurotransmitter
precursors such as L-dopa and 5 –
hydroxytryptophan, along with carbidopa.
Supplementation with follinic acid in patient with
DPHR deficiency.
Some drugs such as trimethoprim-sulfamethoxazole,
methotrexate,and other antileukemic agents are
known to inhibit DHPR enzyme activity and should
be used in great causion in patients with BH4
deficiency .

26. Gene therapy:
 A functional recombinant PAH gene is targeted to the liver, since the activity of PAH is
primarily in the liver.
 Fang et al. (1994) infused a recombinant adenoviral vector containing the human PAH-
cDNA into the liver through the portal vein of PKU mice.
 Within one week, complete normalization of the serum phenylalanine levels was achieved
in these PKU mice .
 Furthermore, correction did not persist beyond 40 weeks with blood phe returning to
pretreatment levels .
 The use of self-complementary AAV vectors resulted in normalisation of
hyperphenylalaninaemia for up to 80 weeks in both males and females .
 Although correction in females was achieved, gender specific differences were also
apparent using this vector, and therefore larger doses of the vector had to be used for
females.

27. Dietary therapy:
 To prevent any irreversible neurological damage that results from excess blood
and consequently brain Phe in PKU patients, dietary treatment must commence
in the neonatal period and adhered to for life.
 Complications :
 (I) dietary compliance due to unpalatability of the diet;
 (II) persisting neurological or psychosocial issues and poor quality of life despite
early intervention;
 (III) potential nutritional deficiencies resulting from restrictive diet;
 (IV) financial burden due to the cost of special medical food and dietary
supplements.

28. Other treatments :
Enzyme therapy
Phenylalanine ammonia-lyase (PAL)
PAL is an enzyme that catalyses the conversion of Phe to transcinnamic acid and
insignificant amounts of ammonia .
Unlike the mammalian enzyme (PAH), PAL is a monomer and requires no
cofactors .
Oral administration is one of the most convenient ways of delivering drugs, as it is
less invasive than intravenous or subcutaneous injections. However, in general oral
delivery of enzymes have been complicated by the low gastric pH.
To increase oral bioavailability of enzymes, various strategies have been
used, such as encapsulation of the protein or the use of live
microorganisms as delivery system.

29. • Probiotics : “live microorganisms which, when
administered in adequate amounts, confer a health
benefit on the host”
*Bifidobacteria
*lactic acid bacteria

30. References:
1) Matalon R, Michals K. Phenylketonuria: screening, treatment and maternal
PKU. [PubMed]
2) Gonzalez, Jason; Willis, Monte S. (Feb 2010). "Ivar Asbjorn Folling
Discovered Phenylketonuria (PKU)". Lab Medicine. 41 (2): 118–119.
3) Marsden DL, Rohr FJ, Costas KC. Inborn errors of metabolism: Nutritional
Management of Phenylketonuria. In: Benjamin C, editors. Encyclopedia of
Human Nutrition. Oxford: Elsevier, 2005:22-7.
4)Williams, Robin A; Mamotte, Cyril DS; Burnett, John R
(2008). "Phenylketonuria: An Inborn Error of Phenylalanine Metabolism". The
Clinical Biochemist.