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Test Code GCK KN GCK Known

Clinical System Name

GCK Known Mutation Analysis


Glucokinase gene



This test involves targeted analysis for mutations previously identified through clinical testing of a family member or  research testing of the individual.  For full gene sequencing please see GCK Sequencing.


GCK testing is indicated for individuals with the following clinical features:

  1. Mild fasting hyperglycemia (100-145 mg/dl) that is stable over months to years
  2. OGTT 2 hour glucose increment is usually <80 mg/dl
  3. May have history of gestational diabetes that does not resolve post-partum
  4. May have a family history of mild type 2 or gestational diabetes

Sample Requirements

Specimen: Whole blood, cord blood

Container(s): Lavender/EDTA, Yellow/ACD A or B

Preferred Vol: 3 mL

Minimum Vol: 1 mL


Note: Heparin samples (Green tops) are unacceptable.


Specimen: Extracted DNA

Minimum: 10µg

Note: DNA concentration minimum 50 µg/mL; 260/280 ratio 1.70-2.00


Specimen: Cultured cells

Acceptable:  Fibroblasts

Container(s): T-25 flasks

Preferred Vol: 2 flasks



Processing Instructions

Reject due to: Heparin

Spin: No

Aliquot: No

Temp: Refrigerate

Storage location: Molecular Genetics box in CPA refrigerator #2


Off-site collection: Refrigerate blood samples until ready to ship.  Transport all sample types at room temperature via overnight shipping.


Specimen Type Temperature Time
Cultured cells Room temp 3 days
Whole blood, extracted DNA Room temp 3-5 days
Whole blood, extracted DNA Refrigerated 7 days
Extracted DNA Frozen ok


Note: Whole blood samples > 7days may be submitted to be assessed by our lab for acceptability for testing.


STAT Performed TAT
Contact lab Monday - Friday 2-3 weeks


Performing Laboratory

Seattle Children's Laboratory


Department:  Molecular Genetics Laboratory

Phone: 206-987-3872


Lab Client Services: 206-987-2617


Lab Genetic Counselors:

Reference Range

Interpretive report will be provided


Method: PCR + Sequencing


Limitations: This test is for targeted known mutation analysis only.  Mutation(s) must be known.

CPT Codes

81403 (updated 1/19/16 jconta)

Special Instructions

Please provide copies of proband reports when requesting known mutation analysis for cases NOT performed by Seattle Children's Lab.


Links to:


Molecular Genetics

Clinical Utility

Maturity-Onset Diabetes of the Young (MODY) is an autosomal dominant form of diabetes typically occurring before age 25 and caused by a primary insulin secretion defect. MODY is not a single entity but represents nine classifications with genetic, metabolic, and clinical heterogeneity. MODY is estimated to affect approximately 1-2% of people with diabetes, although this may be an underestimate since the genetic etiology of this type of diabetes often goes undiagnosed.

Main features of MODY patients include the following: 1) Hyperglycemia usually diagnosed before age 25 years in at least 1 family member. 2) Autosomal dominant inheritance through at least 3 generations, and a phenotype shared by diabetic family members. 3) Absence of insulin therapy or significant C-peptide levels even in a patient on insulin treatment for several years after diagnosis.

MODY 2 (GCK): Approximately 25% of MODY is caused by mutations in the glucokinase (GCK) gene. It is associated with a mild form of nonprogressive hyperglycemia that is usually managed with diet alone. Individuals with GCK MODY rarely have overt symptoms of diabetes, and diabetes-associated complications are rare. These individuals are often diagnosed with diabetes or glucose intolerance on routine screening, particularly during pregnancy. Approximately 2-4% of gestational diabetes may be due to GCK mutations.