• 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, and select noncoding variants. Our assay provides a Q30 quality-adjusted mean coverage depth of 350x (50x minimum, or supplemented with additional analysis). Variants classified as pathogenic or likely pathogenic are confirmed with orthogonal methods, except individual variants that have high quality scores and previously validated in at least ten unrelated samples.

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