• Turnaround time:
    10–21 calendar days (14 days on average)
  • Preferred specimen:
    3mL whole blood in a purple-top tube
  • Alternate specimens:
    DNA or saliva/assisted saliva
  • Sample requirements
  • Request a sample kit




Associated disorders

The GCH1 gene is associated with autosomal dominant dopa-responsive dystonia (DRD) (MedGen UID: 342121). It is also associated with autosomal recessive GTP cyclohydrolase deficiency (MedGen UID: 75683).

Loss-of-function pathogenic variants in GCH1 are the most common cause of dopa-responsive dystonia, accounting for nearly 90% of all cases when sequence analysis is augmented by quantitative methods to detect copy number variants.

GCH1 encodes GTP cyclohydrolase I, the enzyme that catalyzes the first step in the biosynthesis of tetrahydrobiopterin.

Assay and technical information

Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).

Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence in the transcript listed below. In addition, analysis covers the select non-coding variants specifically defined in the table below. Any variants that fall outside these regions are not analyzed. Any specific limitations in the analysis of these genes are also listed in the table below.

Our analysis detects most intragenic deletions and duplications at single exon resolution. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. If you are requesting the detection of a specific single-exon copy number variation, please contact Client Services before placing your order.

Gene Transcript reference Sequencing analysis Deletion/Duplication analysis
GCH1 NM_000161.2