Granulin Precursor (GRN), Full Gene Sequencing

CPT Code(s): 81406

Ordering Recommendation: GRN full gene sequencing is recommended for individuals with clinical symptoms of frontotemporal dementia and individuals with a positive family history of frontotemporal dementia.

Synonyms: GRN, Granulin precursor, Alzheimer disease, early-onset Alzheimer disease, dementia, frontotemporal dementia

Methodology: Sanger sequence analysis. The GRN cDNA reference sequence used is NM_000447.3.

Performed: Monday through Friday

Reported: 14 days

Collect: Preferred: whole blood in a lavender top (EDTA) tubes, cultured and uncultured cells

Specimen Volume: Blood: 3 mL whole blood (minimum 1 mL)

Storage/Transport: Refrigerated/Room temperature

Unacceptable Conditions: Grossly hemolyzed or clotted

Stability: One month refrigerated; One month frozen

Reference Interval: by report

Characteristics: Frontotemporal lobar degeneration is a progressive brain disorder that can affect behavior, language, and movement. The symptoms of this disorder usually become noticeable in a person's fifties or sixties.

Inheritance: Autosomal dominant

Cause: Frontotemporal dementia accounts for 5%-10% of all individuals with dementia and 10%-20% of individuals with dementia with onset before age 65 years.

Penetrance: 90% by age 75 years

Analytical sensitivity and specificity: 99%

Limitations: Only the coding and immediate flanking regions of the GRN gene are analyzed by DNA sequencing. Changes in the promoter region and other non-coding regions will therefore not be detected by this assay. In addition, the presence of a large intragenic deletion of the GRN gene (such as the deletion of an exon) will not be detected by sequence analysis. All results should be interpreted in context of clinical findings, relevant history, and other laboratory data.

References: Gene Reviews