Granulin Precursor (GRN), Targeted Variant Sequencing

CPT Code(s): 81403

Ordering Recommendation: Targeted GRN sequencing is recommended for individuals with clinical symptoms of frontotemporal dementia and 1) where either the familial variant is known or 2) the variant has been identified by a research protocol and needs to be confirmed in a clinical laboratory.

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 targeted variant of the GRN gene is analyzed by DNA sequencing. All results should be interpreted in context of clinical findings, relevant history, and other laboratory data.

References: Gene Reviews