Definition:
A genetic disorder caused by deficiency of the enzyme Phenylalanine Hydroxylase, leading to inability to convert phenylalanine → tyrosine.
Metabolic Defect:
Phenylalanine ↑ → forms phenylpyruvate, phenylacetate, phenyllactate.
Clinical Features:
-
Intellectual disability
-
Seizures
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Pale skin & blonde hair (↓ melanin)
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Musty or “mousey” odor in urine
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Eczema
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Developmental delay
Diagnosis:
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Guthrie test (newborn screening)
-
Elevated phenylalanine levels
Treatment:
-
Low-phenylalanine diet
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Special formulas (Lofenalac)
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Avoid aspartame
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Lifelong dietary control
2️⃣ Alkaptonuria
Definition:
A rare genetic disorder due to deficiency of Homogentisate Oxidase, leading to buildup of homogentisic acid.
Metabolic Defect:
Tyrosine & phenylalanine metabolism affected → homogentisic acid accumulates.
Clinical Features:
-
Black urine on standing (oxidizes & turns dark)
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Ochronosis (bluish-black pigmentation of cartilage, ear, sclera)
-
Early-onset arthritis (spine, knee, hip)
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Joint stiffness
Diagnosis:
-
Homogentisic acid in urine
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Urine turns black on exposure to air/alkali
Treatment:
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Vitamin C (slows ochronosis)
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Pain management
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Protein restriction (↓ phenylalanine & tyrosine intake)
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Joint care & physiotherapy
SHORT Differences: PKU vs Alkaptonuria
| Feature | PKU | Alkaptonuria |
|---|---|---|
| Enzyme Deficiency | Phenylalanine hydroxylase | Homogentisate oxidase |
| Accumulated Substance | Phenylalanine metabolites | Homogentisic acid |
| Key Symptom | Mental retardation, musty odor | Black urine, ochronosis |
| Treatment | Low-Phe diet | Vitamin C, joint care |
