Test Code: 1877

Childhood Absence Epilepsy: GABRB3 Gene Deletion/Duplication
Test Code: 1877
Turnaround time: 3 weeks

CONDITION DESCRIPTION

Childhood absence epilepsy (CAE), which is a common idiopathic generalized epilepsy, accounts for 10-20% of all epilepsy in children under the age of 16 years. Absence seizures are characterized by a brief loss of consciousness lasting between three and ten seconds and can occur up to 200 times a day. Tanaka et al. (2008) identified three missense mutations in the GABRB3 gene (15q11.2-q12) in four out of 48 families (8%) with remitting CAE.

For patients with suspected childhood absence epilepsy, sequence analysis is recommended as the first step in mutation identification. For patients in whom mutations are not identified by full gene sequencing, deletion/duplication analysis is appropriate.

References:
• Tanaka et al. (2008) Am J Hum Genet, 82:1249-1261.
• OMIM #137192: GABRB3 gene
• OMIM #612269: CAE

GENES
GABRB3

INDICATIONS
This test is indicated for:

  • Confirmation of a clinical diagnosis of childhood absence epilepsy in an individual in whom sequence analysis was negative.
  • Carrier testing in adults with a family history of childhood absence epilepsy in whom sequence analysis was negative.

METHODOLOGY

DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes which cover the entire genomic region.

Please note that a “backbone” of probes across the entire genome are included on the array for analytical and quality control purposes. Rarely, off- target copy number variants causative of disease may be identified that may or may not be related to the patient’s phenotype. Only known pathogenic off-target copy number variants will be reported. Off-target copy number variants of unknown clinical significance will not be reported.

DETECTION

Detection is limited to duplications and deletions. The CGH array will not detect point or intronic mutations. Results of molecular analysis must be interpreted in the context of the patient’s clinical and/or biochemical phenotype.

SPECIMEN REQUIREMENTS

Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood

Type: Whole Blood
Specimen Requirements:
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Saliva
Specimen Requirements:
OrageneTM Saliva Collection kit (available through CEN4GEN) used according to manufacturer instructions.

Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.

SPECIAL INSTRUCTIONS

Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed by another third party provider, please submit a copy of the sequencing report with the test requisition.

RELATED TESTS

  • Sequence analysis of the GABRB3 gene is available and is required before deletion/duplication analysis.
  • Custom diagnostic mutation analysis (test code: 6875) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.