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Test Code GCK SEQ GCK Sequencing

Clinical System Name

GCK Sequencing Analysis Request

Synonyms

Glucokinase gene

MODY2

Description

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.

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.

Stability

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.

Availability

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

 

Performing Laboratory

Seattle Children's Laboratory

Department

Department:  Molecular Genetics Laboratory

Phone: 206-987-3872

 

Lab Client Services: 206-987-2617

 

Lab Genetic Counselor: LabGC@seattlechildrens.org

Reference Range

Interpretive report will be provided

Methodology

Method: Bi-directional sequencing of all exons and exon-intron boundaries

 

Limitations: Mutations in the promoter region, large deletions, large duplications, or rare recombinant mutations may not be detected by this method.

CPT Codes

81406x1     (updated 1/19/2016 by jconta) 

Special Instructions

Links to: DiabetesGenes.org

Requisition

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.
 

GCK sequencing can be performed individually or as part of the MODY panel which includes sequencing of 13 genes.  GCK is also performed as part of the Neonatal Diabetes Panel and Congenital Hyperinsulinism Panel.

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.

 

Rarely, PNDM (permanent neonatal diabetes mellitus) is attributed to inactivating mutations of GCK, the gene encoding glucokinase (hexokinase IV). Carrier parents have mild diabetes mellitus or glucose intolerance (GCK-MODY).