Tetrahydrobiopterin Deficiency

Tetrahydrobiopterin deficiency is a rare disorder that increases the levels of several substances, including phenylalanine, in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If tetrahydrobiopterin deficiency is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

High levels of phenylalanine are present from early infancy in people with untreated tetrahydrobiopterin deficiency. Infants with this condition appear normal at birth, but medical problems ranging from mild to severe become apparent over time.

The signs and symptoms of this condition can include:

• intellectual disability,
  
  
• progressive problems with development,
  
  
• movement disorders,
  
  
• difficulty swallowing,
  
  
• seizures,
  
  
• behavioral problems, and
  
  
• an inability to control body temperature.