Alternative titles; symbols
Other entities represented in this entry:
ORPHA: 36387; DO: 0111294;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 2q24.3 | Generalized epilepsy with febrile seizures plus, type 2 | 604403 | Autosomal dominant | 3 | SCN1A | 182389 |
| 2q24.3 | Febrile seizures, familial, 3A | 604403 | Autosomal dominant | 3 | SCN1A | 182389 |
A number sign (#) is used with this entry because generalized epilepsy with febrile seizures plus, type 2 (GEFSP2) and familial febrile seizures-3A (FEB3A) are both caused by heterozygous mutation in the SCN1A gene (182389) on chromosome 2q24.
Heterozygous mutation in the SCN1A gene can also cause Dravet syndrome (607208), which is associated with developmental delay in early childhood.
Generalized epilepsy with febrile seizures plus, type 2 (GEFSP2) is an autosomal dominant neurologic disorder characterized by the onset of seizures associated with fever in the first months or years of life. Affected individuals continue to have various types of febrile and afebrile seizures later in life, including generalized tonic-clonic seizures (GTCS). Some patients may have offset of seizures in the first or second decades; rare patients may have mildly impaired intellectual development. In contrast, patients with isolated febrile seizures (FEB3A) have onset between ages 6 months and 4 years, show spontaneous remission by age 6 years, and have normal cognition. Mutations in the SCN1A gene thus cause a spectrum of seizure disorders, ranging from early-onset isolated febrile seizures to generalized epilepsy with febrile seizures plus, type 2, which represents a more severe phenotype (summary by Scheffer and Berkovic, 1997 and Mantegazza et al., 2005).
For a general phenotypic description and a discussion of genetic heterogeneity of GEFS+, see 604233.
For a phenotypic description and a discussion of genetic heterogeneity of familial febrile seizures, see 121210.
GEFS+ Type 2
Scheffer and Berkovic (1997) reported a large multigenerational Australian kindred in which 23 individuals had seizure disorders beginning in childhood (range, 0.4-9 years; mean, 1.6 years). The patients had a variety of seizure types, but all had generalized tonic-clonic seizures. The seizures could occur with or without associated fever. At least 6 individuals also had other types of seizures, including absence, myoclonic, and atonic. Many had offset of seizures in the first or second decade. All patients had normal neurologic examination and cognition, except for the proband, who was a 20-year-old man with multiple seizure types, EEG abnormalities, and moderately impaired intellectual development. The authors classified the disorder in this family as 'generalized epilepsy with febrile seizures plus' to reflect the wide phenotypic variability.
Baulac et al. (1999) studied a family in which affected individuals in 3 successive generations presented clinical similarities with families with GEFS+. Patients expressed a variable phenotype combining febrile seizures, generalized seizures often precipitated by fever at age greater than 6 years, myoclonic seizures, absence seizures, hemiclonic seizures, and partial seizures, with a variable degree of severity.
Moulard et al. (1999) reported a family in which 6 individuals had isolated typical febrile seizures, and 5 had typical febrile seizures associated with generalized epilepsy. Afebrile seizures occurred in childhood until the teenage years.
Wallace et al. (2001) reported 2 unrelated Israeli families of Ashkenazi Jewish (family B) and Druze (family C) descent with GEFS+. The patients had onset of seizures in the first months or years of life that were associated with fever. Some patients had simple febrile seizures that remitted later in childhood, whereas others had a more complex epileptic syndrome with afebrile seizures and persistence of seizures beyond the second decade. Most patients had normal intellect, although rare patients had mildly impaired intellectual development or learning disabilities; the latter patients had a more severe seizure disorder.
Buoni et al. (2006) reported a 13-year-old boy with GEFS+ who presented in infancy with severe myoclonic seizures that remitted in late childhood and adolescence. He had prolonged febrile seizures at ages 6, 10, and 13 months, afebrile complex partial seizures with secondary generalization beginning at age 18 months, and 2 episodes of status epilepticus at age 2 years. He also had abnormal EEG findings and myoclonic jerks. Antiepileptic medication was unsuccessful. At age 4 years, the seizure frequency decreased in response to medication, and by age 9, he had complex partial seizures with secondary generalization. By age 13, he was treated with valproate and had a febrile seizure. He did not have impaired intellectual development. Buoni et al. (2006) emphasized the relatively benign outcome in this patient despite the more severe phenotype in infancy.
Familial Febrile Seizures 3A
Mantegazza et al. (2005) reported a large Italian family in which at least 12 members spanning 4 generations had simple febrile seizures. The age at onset ranged from 5 months to 4 years, and none had seizures beyond age 6 years. Most seizures were brief, lasting 1 to 5 minutes, although 1 patient had seizures lasting up to 15 minutes. Three affected individuals developed afebrile partial seizures of mesial temporal lobe origin with vegetative or experiential phenomena at the ages of 10, 13, and 11 years. Very rare partial complex seizures or nocturnal secondary generalized tonic-clonic seizures also occurred in all 3 of them. Two of these patients had MRI evidence of unilateral mesial temporal sclerosis. Mantegazza et al. (2005) noted that febrile convulsions had been identified as a risk factor for temporal lobe epilepsy with hippocampal sclerosis (Briellmann et al., 2001). Mantegazza et al. (2005) concluded that the phenotype was distinct from GEFS+ and was most consistent with simple febrile seizures.
The transmission pattern of GEFSP2 in the family reported by Scheffer and Berkovic (1997) was consistent with autosomal dominant inheritance and variable expressivity.
By genomewide linkage analysis of a family with GEFS+ using semiautomated fluorescent genotyping, Baulac et al. (1999) identified a GEFS+ locus on chromosome 2q21-q33. The maximum pairwise lod score was 3.00 with a recombination fraction 0.0 for marker D2S2330. Haplotype reconstruction defined a 22-cM candidate interval flanked by markers D2S156 and D2S2314.
Moulard et al. (1999) also found linkage of GEFS+ to chromosome 2q24-q33.
By linkage analysis of the Australian family with GEFS+ reported by Scheffer and Berkovic (1997), Lopes-Cendes et al. (2000) found linkage to a locus on chromosome 2q23-q31.
By linkage analysis of an Italian family with simple febrile seizures, Mantegazza et al. (2005) found linkage to a locus on chromosome 2q24 designated 'FEB3' by Peiffer et al. (1999).
Escayg et al. (2000) demonstrated that the 2 GEFS+ families reported by Baulac et al. (1999) and Moulard et al. (1999) each carried a different heterozygous mutation in the SCN1A gene (R1648H, 182389.0001 and T875M, 182389.0002, respectively).
In affected members of 3 unrelated families with GEFS+2, Wallace et al. (2001) identified heterozygous missense mutations in the SCN1A gene: family A, the Australian family originally reported by Scheffer and Berkovic (1997) had a D188V mutation (182389.0003); family B, of Ashkenazi Jewish descent, had a V1353L mutation (182389.0004); and family C, of Druze origin, carried an I1656M mutation (182389.0005). Functional studies of the variants and studies of patient cells were not performed, but the authors noted that all occurred in functional domains and may result in neuronal hyperexcitability.
In 2 unrelated Japanese families with GEFS+2 associated with development of partial epilepsy, Sugawara et al. (2001) identified 2 novel mutations in the SCN1A gene. One of these mutations, val1428-to-ala (182389.0011), was a missense mutation in the pore-forming region of the sodium channel, which the authors hypothesized may affect ion selectivity.
In a 13-year-old boy with GEFSP2, Buoni et al. (2006) identified a de novo heterozygous 1-bp deletion in the SCN1A gene (182389.0017).
Orrico et al. (2009) identified 21 mutations, including 14 novel mutations, in the SCN1A gene in 22 (14.66%) of 150 Italian pediatric probands with epilepsy. SCN1A mutations were found in 21.2% of patients with GEFS+ and in 75% of patients with Dravet syndrome (607208) from the overall patient cohort.
Familial Febrile Seizures 3A
In 12 affected members of an Italian family with simple febrile seizures mapping to 2q24, Mantegazza et al. (2005) identified a heterozygous mutation in the SCN1A gene (182389.0015). This disorder is designated FEB3A.
In a 2-stage case-control study including a total of 234 patients with febrile seizures, Schlachter et al. (2009) found a significant association between the major A allele of SNP rs3812718 in the SCN1A gene (182389.0016) and febrile seizures (first stage p value of 0.000017; replication p value of 0.00069). The data suggested that homozygosity for the A allele confers a 3-fold increased relative risk of febrile seizures and may account for a population attributable risk factor of up to 50%. The data were consistent with the hypothesis that low-risk variants with a high population frequency contribute to the risk of common and genetically complex diseases such as epilepsy.
Suls et al. (2010) reported a 4-generation Bulgarian family with epilepsy transmitting a heterozygous 400-kb deletion on chromosome 2q24 encompassing the SCN1A and TTC21B (612014) genes. The phenotype was variable, but all had onset of generalized tonic-clonic seizures around the first year of life (range, 8 to 14 months), and some had myoclonic or absence seizures. Three of 4 patients had febrile seizures in infancy. One patient had mild mental retardation, 1 had psychomotor slowing, and 1 had mental retardation from early infancy; all had reduced seizures on medication. The fourth patient died of status epilepticus at age 13 months. Thus, 2 patients had a phenotype reminiscent of Dravet syndrome, whereas the phenotype in the other 2 was more consistent with GEFS+2. The unaffected father in the first generation was found to be somatic mosaic for the deletion. Suls et al. (2010) noted that deletions involving SCN1A usually result in the much more severe Dravet syndrome, in which affected individuals cannot raise a family and thus do not transmit the mutation. The report of this family with a deletion of SCN1A in which 2 affected individuals were able to raise a family suggested the presence of genetic modifiers and showed intrafamilial variability.
Baulac, S., Gourfinkel-An, I., Picard, F., Rosenberg-Bourgin, M., Prud'homme, J.-F., Baulac, M., Brice, A., LeGuern, E. A second locus for familial generalized epilepsy with febrile seizures plus maps to chromosome 2q21-q33. Am. J. Hum. Genet. 65: 1078-1085, 1999. [PubMed: 10486327] [Full Text: https://doi.org/10.1086/302593]
Briellmann, R. S., Torn-Broers, Y., Jackson, G. D., Berkovic, S. F. Seizures in family members of patients with hippocampal sclerosis. Neurology 57: 1800-1804, 2001. [PubMed: 11723267] [Full Text: https://doi.org/10.1212/wnl.57.10.1800]
Buoni, S., Orrico, A., Galli, L., Zannolli, R., Burroni, L., Hayek, J., Fois, A., Sorrentino, V. SCN1A (2528delG) novel truncating mutation with benign outcome of severe myoclonic epilepsy of infancy. Neurology 66: 606-607, 2006. [PubMed: 16505326] [Full Text: https://doi.org/10.1212/01.WNL.0000198504.41315.B1]
Escayg, A., MacDonald, B. T., Meisler, M. H., Baulac, S., Huberfeld, G., An-Gourfinkel, I., Brice, A., LeGuern, E., Moulard, B., Chaigne, D., Buresi, C., Malafosse, A. Mutations of SCN1A, encoding a neuronal sodium channel, in two families with GEFS+2. (Letter) Nature Genet. 24: 343-345, 2000. [PubMed: 10742094] [Full Text: https://doi.org/10.1038/74159]
Lopes-Cendes, I, Scheffer, I. E., Berkovic, S. F., Rousseau, M., Andermann, E., Rouleau, G. A. A new locus for generalized epilepsy with febrile seizures plus maps to chromosome 2. Am. J. Hum. Genet. 66: 698-701, 2000. [PubMed: 10677328] [Full Text: https://doi.org/10.1086/302768]
Mantegazza, M., Gambardella, A., Rusconi, R., Schiavon, E., Annesi, F., Cassulini, R. R., Labate, A., Carrideo, S., Chifari, R., Canevini, M. P., Canger, R., Franceschetti, S., Annesi, G., Wanke, E., Quattrone, A. Identification of an Na(v)1.1 sodium channel (SCN1A) loss-of-function mutation associated with familial simple febrile seizures. Proc. Nat. Acad. Sci. 102: 18177-18182, 2005. [PubMed: 16326807] [Full Text: https://doi.org/10.1073/pnas.0506818102]
Moulard, B., Guipponi, M., Chaigne, D., Mouthon, D., Buresi, C., Malafosse, A. Identification of a new locus for generalized epilepsy with febrile seizures plus (GEFS+) on chromosome 2q24-q33. Am. J. Hum. Genet. 65: 1396-1400, 1999. [PubMed: 10521305] [Full Text: https://doi.org/10.1086/302621]
Orrico, A., Galli, L., Grosso, S., Buoni, S., Pianigiani, R., Balestri, P., Sorrentino, V. Mutational analysis of the SCN1A, SCN1B and GABRG2 genes in 150 Italian patients with idiopathic childhood epilepsies. (Letter) Clin. Genet. 75: 579-581, 2009. [PubMed: 19522081] [Full Text: https://doi.org/10.1111/j.1399-0004.2009.01155.x]
Peiffer, A., Thompson, J., Charlier, C., Otterud, B., Varvil, T., Pappas, C., Barnitz, C., Gruenthal, K., Kuhn, R., Leppert, M. A locus for febrile seizures (FEB3) maps to chromosome 2q23-24. Ann. Neurol. 46: 671-678, 1999. [PubMed: 10514109] [Full Text: https://doi.org/10.1002/1531-8249(199910)46:4<671::aid-ana20>3.0.co;2-5]
Scheffer, I. E., Berkovic, S. F. Generalized epilepsy with febrile seizures plus: a genetic disorder with heterogeneous clinical phenotypes. Brain 120: 479-490, 1997. [PubMed: 9126059] [Full Text: https://doi.org/10.1093/brain/120.3.479]
Schlachter, K., Gruber-Sedlmayr, U., Stogmann, E., Lausecker, M., Hotzy, C., Balzar, J., Schuh, E., Baumgartner, C., Mueller, J. C., Illig, T., Wichmann, H. E., Lichtner, P., Meitinger, T., Strom, T. M., Zimprich, A., Zimprich, F. A splice site variant in the sodium channel gene SCN1A confers risk of febrile seizures. Neurology 72: 974-978, 2009. [PubMed: 19289736] [Full Text: https://doi.org/10.1212/01.wnl.0000344401.02915.00]
Sugawara, T., Mazaki-Miyazaki, E., Ito, M., Nagafuji, H., Fukuma, G., Mitsudome, A., Wada, K., Kaneko, S., Hirose, S., Yamakawa, K. Na-v-1.1 mutations cause febrile seizures associated with afebrile partial seizures. Neurology 57: 703-705, 2001. [PubMed: 11524484] [Full Text: https://doi.org/10.1212/wnl.57.4.703]
Suls, A., Velizarova, R., Yordanova, I., Deprez, L., Van Dyck, T., Wauters, J., Guergueltcheva, V., Claes, L. R. F., Kremensky, I., Jordanova, A., De Jonghe, P. Four generations of epilepsy caused by an inherited microdeletion of the SCN1A gene. Neurology 75: 72-76, 2010. [PubMed: 20484682] [Full Text: https://doi.org/10.1212/WNL.0b013e3181e62088]
Wallace, R. H., Scheffer, I. E., Barnett, S., Richards, M., Dibbens, L., Desai, R. R., Lerman-Sagie, T., Lev, D., Mazarib, A., Brand, N., Ben-Zeev, B., Goikhman, I., Singh, R., Kremmidiotis, G., Gardner, A., Sutherland, G. R., George, A. L., Jr., Mulley, J. C., Berkovic, S. F. Neuronal sodium-channel alpha-1-subunit mutations in generalized epilepsy with febrile seizures plus. Am. J. Hum. Genet. 68: 859-865, 2001. [PubMed: 11254444] [Full Text: https://doi.org/10.1086/319516]