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GABA Metabolism Deficiency (NGS Panel and Copy Number Analysis)

CPT: 81185, 81405, 81479

Specimen Requirements


Blood | Extracted DNA | Cultured Fibroblasts | Muscle | Buccal Cells


Blood: Draw blood in a lavender top EDTA tube, Sample Stability: 5-7 days, Preferred volume: 4 ml, Minimum volume: 2 ml, DO NOT FREEZE. Extracted DNA: From leukocytes, muscle, or fibroblasts: Preferred quantity: 1 microgram, Minimum quantity: 800 nanograms. Genomic DNA should be eluted in sterile Dnase/Rnase free water or TE. The A260:A280 ratio should be 1.8-2.0. Cultured Fibroblasts: Two T-25 flasks of fibroblasts, preferably ~90% confluent. TAT will be extended by 7-14 days if cells are not confluent upon arrival. Muscle: 50-75 milligrams muscle snap frozen in liquid nitrogen and maintained at -80°Celsius or below. Buccal Cells: One buccal swab should be used for collection. Do not discard solution in collection tube. Follow collection instructions supplied. Stability at ambient temperature is 60 days.


Blood: Lavender-Top (EDTA) Tube, Buccal Swab from MNG Kit, Tissue or Extracted DNA: Sterile screw capped vial, Cultured cells: T25 flask


Blood: Specimens should be shipped overnight in a secure container at room temperature. Extracted DNA: Should be shipped overnight at room temperature. If previously frozen, DNA can be shipped in an insulated container with wet or dry ice. Cultured Fibroblasts: T-25 flasks containing fibroblasts should be shipped in an insulated container at room temperature. Flasks should be completely filled with media and cells should be ~90% confluent. Fibroblast samples must be certified free from Mycoplasma. MNG is able to perform this service for a small charge (TC05). For NGS panels, TAT will be extended by 7-14 days if cells are not confluent upon arrival. Muscle: Samples should be shipped frozen in an insulated container with 5-7 lbs. dry ice, overnight. Buccal cells: Should be shipped overnight in a secure container at room temperature.

Storage Instructions

Blood - ship ASAP, but stable up to 5 days post-collection at room temperature. DO NOT FREEZE; Swab - 60 day post-collection room temperature stability; DNA - ship at room temperature after extraction; Fibroblasts - ship flask in insulated container at room temp or refigerated; Muscle - ship in insulated container with 5-7 lbs of dry ice

Stability Requirements

Room Temperature: Blood - 5 days, Swab - 60 days, DNA - 30 days, Muscle - 0 days, Fibroblasts - 2-3 days; Refrigerated: Blood - 5 days, Swab - 60 days, DNA - 30 days, Muscle - 0 days, Fibroblasts - 2-3 days; Frozen: Blood - DO NOT FREEZE, Swab - 60 days, DNA - Indefinitely, Muscle - Indefinitely, Fibroblasts - Indefinitely; Freeze/Thaw: None

Causes for Rejection

Extracted DNA A260:A280 ratio of outside of 1.8-2.0 range; Frozen blood EDTA tube; Thawed and/or fatty muscle sample; Insufficient buccal cell collection

Test Details


Defects have been reported in 4 steps of the gamma amino butyric acid (GABA) metabolism causing inherited disorders as: glutamate decarboxylase (GAD) deficiency, GABA-transaminase deficiency, succinic semialdehyde dehydrogenase (SSADH) deficiency, and homocarnosinase deficiency. SSADH deficiency is the most common of the inherited disorders of neurotransmitters. GABA-transaminase deficiency and homocarnosinosis appear to be very rare. SSADH deficiency is an autosomal recessive inherited condition characterized by infantile-onset of hypotonia, developmental delay, cognitive impairment, expressive language deficit, and mild ataxia. Epilepsy is present in about half of affected individuals and is more common in adults. Hyperkinetic behavior, aggression, self-injurious behaviors, hallucinations, and sleep disturbances have been reported in nearly half of all affected individuals, more commonly in those who are older. GAD deficiency is inherited in an autosomal recessive manner and is caused by pathogenic variants in the GAD1 gene. GAD1 catalyzes the conversion of glutamic acid to GABA. GAD deficiency is a non-progressive disorder of movement and/or posture. Affected individuals manifest symmetrical, non-progressive spasticity, developmental delay, hypertonia, and sometimes intellectual disability and epilepsy can be part of the clinical picture. GABA-transaminase deficiency is a very rare autosomal recessive condition caused by pathogenic variants in the ABAT gene. The phenotype includes severe intellectual disability, hypotonia, hyperreflexia, lethargy, refractory seizures, high-pitched cry, and EEG abnormalities.


Next-Generation Sequencing

Recommended MNG Kits

SINGLE Blood Genetic Testing, Buccal Swab Genetic Testing