Phenylketonuria – Here Are The Causes and Symptoms

Phenylketonuria - Here Are The Causes And Symptoms

What is Phenylketonuria?

Phenylketonuria (PKU) is a rare genetic error that causes an amino acid called phenylalanine to accumulate in the body.

Accumulation of phenylalanine leads to brain damage, intellectual disabilities, seizures, and behavioral problems.

Phenylketonuria affects 1 in 12,000 children (both males and females). (1, 2)

What causes Phenylketonuria?

Phenylketonuria is an autosomal recessive inherited disorder caused by the mutation of the phenylalanine hydroxylase(PAH) gene.

The mutation in the PAH gene leads to low production of the enzyme phenylalanine hydroxylase, which is an enzyme that converts phenylalanine to tyrosine. 

Tyrosine is one of the 20 useful amino acids in the body.

Tyrosine is needed in the creation of neurotransmitters such as epinephrine, norepinephrine, and dopamine.

The absence of phenylalanine hydroxylase and the inability to convert phenylalanine leads to the accumulation of dietary phenylalanine in the body over time.

Phenylalanine is found in all protein sources and most artificial sweeteners.  

Phenylketonuria is inherited as an autosomal recessive disorder; therefore, a person needs two copies of the mutated gene from both parents to have it.

Those with one mutated copy don’t usually manifest any symptoms. (3, 4)

What are the symptoms of Phenylketonuria?

Here are the signs and symptoms of Phenylketonuria:

  • Small head
  • Low birth weight
  • Stunted growth
  • Musty smell from sweat and urine
  • Seizures (more common in older children)
  • Lighter skin and hair (hypo-pigmentation)
  • Intellectual disabilities (learning difficulties)
  • Behavioral problems, for instance, attention deficit hyperactivity disorder (ADHD)
  • Mood disorders (depression, anxiety)
  • Eczema
  • Tremors or trembling (common in young children)

Classifications Of Phenylketonuria:

There are two types of Phenylketonuria based on the minimal presence or complete absence of phenylalanine hydroxylase.

  • Classic PKU: is the complete absence of the enzyme phenylalanine hydroxylase, and it is the most severe form of Phenylketonuria.
  • Variant PKU (non-PKU hyperphenylalaninemia): is the less severe form of Phenylketonuria.

How is Phenylketonuria diagnosed?

  • Neonatal heel prick test: blood is collected from the heel of the newborn to check for elevated levels of phenylalanine.
  • Tandem mass spectrometry (MS/MS): measures the amount of Phenylalanine concentration and the ratio of Phenylalanine to Tyrosine. (The ratio is typically elevated).

How is Phenylketonuria treated?

Sadly, there is no cure, but symptoms can be relieved by several medical techniques such as: 

Phenylketonuria Diet

Diet is the main way to manage Phenylketonuria.

Foods high in phenylalanine such as protein-rich foods (meat, milk, beer, cheese, eggs, nuts, beans, fish) and artificial sweeteners should be limited/removed from the diet. 

Babies can still drink breast milk for a while.

Still, special formulas such as Lofenalac are also needed for consumption by babies.

Lofenalac contains all other amino acids except phenylalanine. 

All patients with Phenylketonuria will have to take PKU Formulas for the rest of their lives to receive an adequate amount of proteins without consuming phenylalanine.

With the help of a nutritionist, special meal plans are made to fit the need of a patient with Phenylketonuria. (5)

FDA approved phenylketonuria medication; Sapropterin (Kuvan)

Sapropterin lowers phenylalanine levels, and it is known to be effective in mild cases of Phenylketonuria (early stage of the disease).

For more information about phenylketonuria (PKU), you should talk to your physician.