Phenylketonuria (PKU): Causes, Symptoms, and Treatment Explained

Phenylketonuria (PKU): Causes, Symptoms, and Treatment Explained

Phenylketonuria.
Answer:

• It is a common metabolic disorder.

Phenylketonuria Causes:

• Deficiency of the hepatic enzyme phenylalanine hydroxylase.

Phenylketonuria Mechanism:

1. Deficiency of enzyme phenylalanine hydroxylase
↓

Impairs synthesis of tetrahydrobiopterin
↓
Causes accumulation of phenylalanine in tissues and blood.
↓
Excess of it is excreted in the urine.

2. Phenylalanine is diverted to alternate pathways.

• This results in the excessive production of

1. Phenylpyruvate
2. Phenylacetate
3. Phenyllactate
4. Phenylglutamine.

Phenylketonuria Clinical Features:

1. Effects of CNS:

• Mental retardation.
• Failure to walk or talk.
• Retarded growth
• Seizures and tremor
• Low IQ

2. Effect on pigmentation:

• Hypopigmentation due to impaired melanin formation.

3. Urine:

• Contains phenylalanine and its metabolic products.
• Mousey odor – due to the presence of phenylacetate.

Phenylketonuria Diagnosis:

• Detected by screening newborn babies.

1. Guthrie test.

• It is a bacterial bioassay for phenylalanine.

2. Ferric chloride test.

• Detects phenylpyruvate in urine.
• The positive test gives green color.

Phenylketonuria Treatment:

• Intake of the diet with low phenylalanine content
• Synthetic amino acid preparations can be used.
• As tyrosine cannot be synthesized, it should be provided in the diet.
• In serious conditions – 5 – hydroxytryptophan and dopa are administered.
• This restores the synthesis of serotonin and catecholamines.