GTP Cyclohydrolase I Deficiency

GTP Cyclohydrolase I (GTPCH1) deficiency is a disorder of the BH4 biosynthesis pathway, presenting with hyperphenylalaninemia (HPA) associated with monoamine neurotransmitter deficiency. Symptoms of this disorder include mental retardation, convulsions, tone and posture disturbances, drowsiness, irritability, abnormal movements, recurrent hyperthermia without infections, hypersalivation, and swallowing difficulties. The high levels of phenylalanine are often detected on newborn screening.

Tests Available

Forms and Documents

Test Details

  • Confirmation of a clinical diagnosis
  • Selection of appropriate treatment
  • Identification of at-risk family members


3 weeks
2-5 mL Blood - Lavender Top Tube
Buccal Swabs

*Reporting times are typical, but could be extended in situations outside GeneDx's reasonable control.


81405x1, 81479x1
  • 270.1 Phenylketonuria [PKU], Hyperphenylalaninemia
  • 781 Symptoms involving nervous and musculoskeletal systems Excludes: depression NOS (311) disorders specifically relating to: back (724.0-724.9) hearing (388.0-389.9) joint (718.0-719.9) limb (729.0-729.9) neck (723.0-723.9) vision (368.0-369.9) pain in limb (729.5)
For price inquiries please email

**The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.


  1. Muller Y et Al., (1998) Neurogenetics 1:165-177.
  2. Ichinose H et Al., (1994) Nat Genet 8:236-242.
  3. Bandmann O et Al., (1996) Hum Molec Genet 5:403-406.
  4. Furukawa Y et Al., (1998) Ann Neurol 44: 10-16.
  5. Furukawa Y et Al., (1998) Neurology 50:1015-20.
  6. Muller U et Al., (2002) J Neural Transm 109:321-328
  7. Furukawa Y, (2004) Adv Neurol 94:127-138.
  8. Hagenah et Al., (2005) Neurology 64:908-911.
  9. Thony B and Blau N, (2006) Hum Mutat 27:870- 878.
  10. Zirn B et Al., (2008) J Neurol Neurosurg Psych 79:183-186.
  11. Clot F et Al., (2009) Brain 132: 1753-1763.
  12. Furukawa Y, (2009) Gene Reviews GTPCH1-Deficient DRD.