Type 3
Patients with GEFS+ type 3 have mutations in the GABRG2 gene, which encodes the GABAA γ2 subunit (figure 2). The first mutation discovered in GABRG2 was K289M, in the extracellular region linking membrane-spanning domains M2 and M3. Oocytes injected with α1, β2, and γ2 subunits produce large GABA inducible currents whereas those injected with K289M mutant instead of wild-type subunits produce currents much smaller (about 10% of wild-type). This abnormal current is not the result of non-incorporation of mutant subunits since mutant containing receptors are still sensitive to benzodiazepines, a property for which functional γ subunits are required. Because of these results, it is believed that the GEFS+ phenotype in these individuals is a result of hyperexcitability.Concurrent with the previous mutation, a second group found a second mutation in GABRG2 associated with GEFS+. This mutation, R43Q, is located in the one of two benzodiazepine binding-sites located in the extracellular N-terminus. Benzodiazepines, such as Diazepam, potentiate GABA induced current. This potentiation is abolished in cells expressing the R43Q mutant subunit instead of the wild-type γ subunit. This mutation does not affect the subunits ability to coassemble into function receptors as it still confers resistance to GABA current blockade by zinc. As with the previous mutation, this mutation is expected to result in neuronal hyperexcitability.The final known GEFS+ type 3 mutation is a nonsense mutation, Q351X, located in the intracellular  region linking the third and fourth membrane spanning segments.
An abscess of the thymus (also known as "Dubois abscesses") is a condition that is one of many possible causes of cysts in the mediastinum. It can present with chest pain behind the sternum.It can be associated with congenital syphilis.Although the thymus is usually classified with the immune system, thymic diseases are classified with endocrine disorders in ICD-9 and ICD-10. References


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