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| Specimen | Whole blood |
| Volume | 7 mL |
| Minimum Volume | 3 mL |
| Container | Lavender-top (EDTA) tube or yellow-top (ACD) tube |
| Storage Instructions | Maintain at room temperature or refrigerate at 4°C. |
| Causes for Rejection | Frozen or hemolyzed specimen; quantity not sufficient for analysis; improper container |
| Use | Severe myoclonic epilepsy of infancy (SMEI, OMIM: 607208), also known as Dravet syndrome, is an autosomal-dominant epilepsy and seizure disorder of childhood onset. The incidence is 1 in 50,000 to 1 in 20,000, with males more commonly affected, 2:1. The first seizures are febrile or generalized tonic, clonic, or tonic-clonic, and appear as early as age one month and typically in the first year. They increase in frequency and severity with time, and by age one year the seizures are most often myoclonic, although other types, such as absence, partial, and atonic seizures can also occur. As the disease advances, both psychomotor and cognitive growth begin to slow and eventually decline. Half of all SMEI patients suffer from ataxia and cognitive impairment, and 50% have an IQ <50. As many as 20% will die between the ages of three and five years. SMEI represents the severe end of a continuum of seizure disorders with overlapping features. SMEI, as well as severe myoclonic epilepsy of infancy borderline (SMEB), intractable childhood epilepsy with generalized tonic clonic seizures (ICEGTC), and generalized epilepsy with febrile seizures plus (GEFS+, OMIM:604233), can each be caused by mutations in the neuronal voltage-gated sodium channel subunit α (SCN1A) gene on chromosome 2p24. Although many mutations are de novo, some cases are familial. Consequently, testing is recommended for the parents of any child with an SCN1A mutation. |
| Limitations | Direct gene sequencing will detect all coding region variants within the SCN1A gene. Variants in control elements, deep within introns, or in other genes, will not be detected.
Results of this test are for investigational purposes only. The performance characteristics of this assay have been determined by LabCorp. The result should not be used as a diagnostic procedure without confirmation of the diagnosis by another medically established diagnostic product or procedure. |
| Methodology | Polymerase chain reaction (PCR); direct gene sequencing |
| References | Claes L, Ceulemans B, Audenaert D, et al. De Novo SCN1A mutations are a major cause of severe myoclonic epilepsy of infancy, Hum Mutat. 2003 Jun; 21(6):615-621. PubMed 12754708
Mulley JC, Scheffer IE, Petrou S, Dibbens LM, Berkovic SF, Harkin LA. SCN1A mutations and epilepsy. Hum Mutat. 2005 Jun; 25(6):535-542. PubMed 15880351 National Institute of Neurological Disorder and Seizures. Seizures and Epilepsy: Hope Through Research. National Institutes of Health Publications N° 04-156, originally published May 2004; updated March 2, 2006. Available at: http://www.ninds.nih.gov/disorders/epilepsy/detail_epilepsy.htm |
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