1. Disorders of aromatic amino acid metabolism (Phenylalanine, tyrosine)
Dr. Ketki K Assistant Professor Department of Biochemistry

2. Inborn error of Phenylalanine & tyrosine metabolism (IEM)

3. IEM Cause: Mutant genes results in Abnormal enzyme/
Total loss of enzyme activity/
Partial deficiency of enzyme
Further leads to accumulation of substrate &
No product formation

4. IEM of Phe & Tyr Phenylketonuria (PKU) Alkaptonuria Tyrosinemia
Albinism

5. PKU Most common IEM, Autosomal Recessive Incidence- 1: 10,000 Types:
Type I- Classical: deficiency of Phenylalanine hydroxylase
Type II & III: deficiency of Dihydro biopterin reducase
Type IV & V : deficiency of enzyme synthesizing biopterin
Elevated blood phenylalanine may not be detectable until 3–4 days postpartum. False-positives in premature infants may reflect delayed maturation of enzymes of phenylalanine catabolismphenylalanine, which becomes a major donor of amino groups in aminotransferase activity and depletes neural tissue of a-ketoglutarate. This absence of a-ketoglutarate in the brain shuts down the TCA cycle and the associated production of aerobic energy, which is essential to normal brain development.
phenylpyruvic acid, is reduced to phenylacetate and phenyllactate, and all 3 compounds appear in the urine. The presence of phenylacetate in the urine imparts a "mousy" odor.
deficiencies in DHPR can manifest with hyperphenylalaninemia. However, since tetrahydrobiopterin is a cofactor in several other enzyme catalyzed reactions (e.g. see the synthesis of the tyrosine- and tryptophan-derived neurotransmitters as well as nitric oxide in Specialized Products of Amino Acids), the effects of missing or defective DHPR cause even more severe neurological difficulties than those usually associated with PKU caused by deficient phenylalanine hydroxylase activity.

6. BH4 required for
Phenylalanine hydroxylase = synthesis of tyrosine
tyrosine hydroxylase = synthesis of catecholamines(NT)
tryptophan hydroxylase = synthesis of Serotonin
Deficiency of BH4 leads to ↓ tyrosine, dopamine,serotonin in brain

7. Consequences/biochemical abnormalities

9. 1) Hyperphenylalaninemia (>20 mg/dL)
↑ phenylalnine in tissue, plasma,urine
2)↑phenyllactate,phenylacetate,phenylpyruvate
excreted in urine
These metabolites give urine : "mousy" odor.

10. C/F
Mental Retardation (low IQ<50),intellectual disability (low IQ),developmental delay, microcephaly, hyperactivity,seizures,agitation
Hypopigmentation (elevated phenylalanine competitively inhibits tyrosinase & impairs melanin formation) that causes light skin color,fair hair, blue eyes etc
Mousy body odor (due to presence of phenyllactic acid in sweat)

11. Laboratory diagnosis & screening
Blood phenylalanine: Normal level 1 mg/dL
In PKU, level > 20 mg/dL
diagnosed by chromatography, Tandem mass spectroscopy (TMS)
Time of blood collection in new born: hrs after protein feeding/breast feeding
(to avoid false negative results)
Mother clears increased phenylalanine in her affected fetus through placenta

12. 2) Ferric chloride test: blue-green 3) Guthrie’s test: blood/urine: b
2) Ferric chloride test: blue-green 3) Guthrie’s test: blood/urine: b. subtilis 4) DNPH test : Yellow ppt 5) HPLC 6) Prenatal diagnosis by using : cultured amniotic cells

14. Treatment 1) Diet low in phenylalanine (tapioca/cassava)/
synthetic amino acid preparation free of
phenylalanine supplemented with some
natural foods
(fruits,vegetables, cereals) selected for their
low phenylalanine content
Treatment must begin during first 7-10 days
of life to prevent neurological impairment)
Lifelong restriction of phenylalanine is
recommended

15. 2) supply tyrosine In diet
3) supplementation with BH4 &
L-3,4-dihydroxyphenylalnine(L-DOPA) &
5- hydroxytryptophan
Improves clinical outcome in type II,III.IV, v PKU

16. Maternal PKU:
Lady having PKU,but not on low Phe diet becomes pregnant
Then the offspring develops “Maternal PKU syndrome”.
It causes microcephaly & congenital heart abnormalities in fetus.
It can be prevented by dietary restriction of diet containing phenylalanine in mother prior to pregnancy & maintain throughout pregnancy

18. Alkaptonuria Autosomal recessive, incidence 1 in 2,50,000 births
Metabolic defect: Deficiency of Homogentisic acid oxidase
Consequences: increased homogentisic acid in urine
Arthritis due to binding of HGA to cartilageThe first genetic disease ever recognized, was demonstrated to be the result of a defect in phenylalanine and tyrosine catabolism.
Garrod’s tetrad: alkaptonuria,albinism, pentosuria,cystinuria

19. Biochemical manifestation

20. C/F:
Patient asymptomatic until age 40 years
Urine gets darken on exposure to air
Dark staining of diapers indicate disease in infants
Large joint arthritis, Ochronosis (deposition of black pigment/alkapton bodies on cartilage & collagenous tissue)

22. Investigations:
Urine: black on standing
Ferric chloride test: green color
Benedict’s test: orange-red color
HPLC

23. Treatment:
Not life threatening condition so no specific treatment required
Diet low in phenylalanine & tyrosine

24. Albinism Autosomal recessive, Incidence: 1 in 20,000
Due to deficiency in synthesis of pigment melanin which is due to absence of tyrosinase (copper containing enzyme) in eye & skin [ c/a tyrosinase negative oculocutaneous albinism ]
When tyrosinase or melanin forming cells are absent from epidermis leukoderma results

25. Hypopigmentation of skin, fundus & iris
Associated Photophobia,nystagmus,↓ visual acuity
Skin sensitivity to sunlight, prone to skin cancer(melanoma)

27. Tyrosinemia
1)Type I Tyrosinemia: Hepatorenal -Tyrosenemia 2) Type II Tyrosinemia: Oculocutaneous- Tyrosenemia 3) Type III Tyrosinemia : Neonatal Tyrosenemia 4) Hawkinsinuria

28. 1)Type I Tyrosinemia: Hepatorenal -Tyrosinemia
Also c/a tyrosinosis AR
Incidence: 1.5 per 1,000 births
Cause: def of Fumaryl acetoacetate hydrolase

29. C/F:
Cabbage like odor
Hypoglycemia
Liver failure, renal tubular dysfunction
Vitamin D resistant rickets
Mild Mental Retardation,
Death may occur in first 6 months of life

30. Investigation:
Urine contains tyrosine, pHPPA,hydroxyphenyllactic acid
Serum: shows tyrosine
Treatment:
Tyrosine & phenylalanine restricted diet

31. Type II Tyrosinemia: Oculocutaneous- Tyrosinemia
C/a Richner-Hanhart syndrome
Cause: deficiency of tyrosine transaminase
Consequences : urinary excretion of
tyrosine,tyramine
C/F: Mental retardation, dermatitis, palmoplantar keratosis, photophobia
Treatment: diet low in phe,tyr

32. Type III Tyrosinemia : Neonatal Tyrosinemia
Due to def of p-hydroxy phenylpyruvate hydroxylase Temporary condition Overcome by treatment with ascorbic acid

33. Hawkinsinuria Autosomal dominant Due to def of p-HPPA oxidase
Excretion of p-HPPA in urine

35. Case 1 2 weeks infant: convulsions, mousy odor in urine,
Ferric chloride test; green

36. Plasma phenylalanine ↑increased
Urine Phenylalanine, Phenylpyruvate,
Phenyllactate ↑

37. What is the importance of early diagnosis?
What is the defect?
Why convulsions?
Why fair skin?
What is the importance of early diagnosis?
Convulsion; decreased neurotransmitter synthesis (serotonin) by Ph alaniane + direct toxicity + decreased GABA synthesis
Diagnosis: can prevent mental retardation
Fair skin: phenylalanine blocks tyrosinase

38. Case 2 3 yrs child is having white hair + fair skin
addition of THB had no effect
What is the biochemical defect?
Will there be any abnormality of catecholamine metabolism?
No effect on catecholamine met as they are forme in adrenal medulla from a totally different enzyme. And melanin inside melanocytes

39. Case 3
Mother of 1.5 year old child came with complaint of progressive appearance of hyperchromic papules on his second fingers of both hands since 1 year. he also had darkening of urine & diaper.
What is the diagnosis?

40. "Once you start a working on something, don't be afraid of failure and don't abandon it. People who work sincerely are the happiest." Chanakya quotes (Indian politician, strategist and writer, 350 BC-275BC)