Alternative titles; symbols
ORPHA: 36387; DO: 0111302;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 19q13.11 | Generalized epilepsy with febrile seizures plus, type 1 | 604233 | Autosomal dominant | 3 | SCN1B | 600235 |
A number sign (#) is used with this entry because of evidence that generalized epilepsy with febrile seizures plus type 1 (GEFSP1) is caused by heterozygous mutation in the SCN1B gene (600235) on chromosome 19q13.
Generalized epilepsy with febrile seizures plus type 1 (GEFSP1) is an autosomal dominant neurologic disorder characterized by onset of seizures associated with fever in infancy or early childhood. There is wide phenotypic variability, even within families. In contrast to classic febrile seizures (see, e.g., FEB1, 121210), which affect approximately 3% of children under 6 years of age and typically spontaneously remit by age 6 years, patients with GEFSP1 either have febrile seizures extending beyond age 6 years or develop epilepsy with afebrile seizures. Other seizure types include absence seizures, partial seizures, myoclonic seizures, and atonic seizures. Some patients may have developmental delay after the onset of seizures (summary by Wallace et al., 1998 and Singh et al., 1999).
Deprez et al. (2009) reviewed the genetics of epilepsy syndromes starting in the first year of life, and included a diagnostic algorithm.
Genetic Heterogeneity of GEFS+
GEFS+ is a genetically heterogeneous disorder. See also GEFS+2 (604403), caused by mutation in the SCN1A gene (182389) on chromosome 2q24; GEFS+3 (see 607681), caused by mutation in the GABRG2 gene (137164) on chromosome 5q34; GEFS+5 (613060), associated with variation in the GABRD (137163) gene on chromosome 1p36; GEFS+9 (616172), caused by mutation in the STX1B gene (601485) on chromosome 16p11; GEFS+10 (618482), caused by mutation in the HCN1 gene (602780) on chromosome 5p12; GEFS+11 (602477), caused by mutation in the HCN2 gene (602781) on chromosome 19p13; and GEFS+12 (620755), caused by mutation in the SLC32A1 gene (616440) on chromosome 20q11.
Several putative loci have also been identified; see GEFS+4 (609800), mapped to chromosome 2p24; GEFS+6 (612279), mapped to chromosome 8p23-p21; GEFS+7 (613863), mapped to chromosome 2q24; and GEFS+8 (613828), mapped to chromosome 6q16.3-q22.31.
Singh et al. (1999) reported a large multigenerational family from Tasmania in which 26 individuals had onset of febrile seizures in the first years of life. Sixteen patients had classic febrile seizures and 10 had GEFS+ with seizures occurring beyond age 6 years and/or also developed afebrile seizures, including generalized tonic-clonic seizures (GTCS), absence seizures, myoclonic seizures, and atonic seizures. There was wide phenotypic severity. Most had onset in the first year of life and many had remittance of the seizures in the first or second decades, although some had seizures into adulthood. The proband, who was the most severely affected family member, was a 29-year-old woman with intractable myoclonic-astatic seizures. Although specific details were lacking, most patients apparently had normal intellectual development. Several additional family members had unclassified or unconfirmed seizures, which may have represented phenocopies.
Wallace et al. (2002) reported a large Australian family with GEFS+ type 1. The proband developed fever-associated generalized tonic-clonic seizures at age 18 months. These continued until he was 3 years old, at which time he developed afebrile seizures, including absence seizures. He later noted sensory aura preceding complex partial seizures or GTCS. At age 14 years, neurologic examination and brain MRI were normal, whereas EEG showed generalized spike wave activity and, on one occasion, right temporal epileptiform activity. His phenotype was designated FS+, followed by partial epilepsy of the temporal lobe type. Family history showed 19 individuals with seizures, including GEFS+ and febrile seizures.
Audenaert et al. (2003) reported a family with GEFS+ type 1. The phenotype was unusual in that the proband presented with afebrile absence seizures at age 17 months and never had febrile seizures. However, her older brother had classic febrile seizures. Her mother was unaffected, but 2 maternal uncles and a first cousin had febrile seizures that remitted by age 7 years.
Grinton et al. (2022) examined 14 unrelated families with GEFS+, all segregating the same heterozygous mutation in the SCN11B gene (C121W; 600235.0001). Six families had previously been reported. All individuals with the mutation included in the study had epilepsy phenotypes consistent with GEFS+, varying from unaffected to severe (Dravet syndrome). The most common phenotypes observed in the families were febrile seizures and febrile seizures plus. Among the patients studied, 12 of 44 had no known history of seizures, giving a penetrance of approximately 70%. The authors noted that the mild phenotype with incomplete penetrance associated with the mutation is consistent with an autosomal dominant childhood-onset disease that has persisted in the population.
The transmission pattern of GEFSP1 in the families reported by Wallace et al. (1998) and Wallace et al. (2002) was consistent with autosomal dominant inheritance and incomplete penetrance.
In affected members of a large Tasmanian family with GEFS+ (Singh et al., 1999), Wallace et al. (1998) found linkage to chromosome 19q13.1 and identified a heterozygous missense mutation in the voltage-gated sodium channel beta-1 subunit gene, SCN1B (C121W; 600235.0001). In vitro functional expression studies indicated that the mutation interfered with channel-gating kinetics, consistent with a loss-of-function effect.
Wallace et al. (2002) identified a heterozygous C121W mutation in another Australian family with GEFS+. Four unaffected individuals carried the mutation, indicating reduced penetrance.
In affected members of a family with GEFS+ type 1, Audenaert et al. (2003) identified a heterozygous splice site mutation in the SCN1B gene (600235.0002). The penetrance of the disorder was estimated to be 63%.
Grinton et al. (2022) examined 14 unrelated families from Australia, the United Kingdom, and the United States with GEFS+, all with the same heterozygous c.363C-G mutation in the SCN1B gene (C121W; 600235.0001). The authors identified a core ancestral haplotype spanning about 260 kb that was shared by all 14 families. The age of the most recent common ancestor of these 14 families was estimated at 31.2 generations or about 800 years earlier. The penetrance of this variant in these multigenerational families was about 70%. Analysis of UK Biobank whole-exome sequencing data identified the heterozygous variant in 74 (0.039%) unrelated persons. Most of these carriers (89%) shared the full core ancestral haplotype, while the others shared smaller regions of the core haplotype. All 74 shared segments of the extended haplotype outside the core haplotype region. The variant was seen 14 times more often in the European cohort of the UK Biobank than in the gnomAD database, supporting the variant being of British origin. The authors concluded that variants that are present in the population at low frequencies should be considered as potentially pathogenic when the phenotype is mild and incompletely penetrant.
Audenaert, D., Claes, L., Ceulemans, B., Lofgren, A., Van Broeckhoven, C., De Jonghe, P. A deletion in SCN1B is associated with febrile seizures and early-onset absence epilepsy. Neurology 61: 854-856, 2003. [PubMed: 14504340] [Full Text: https://doi.org/10.1212/01.wnl.0000080362.55784.1c]
Deprez, L., Jansen, A., De Jonghe, P. Genetics of epilepsy syndromes starting in the first year of life. Neurology 72: 273-281, 2009. [PubMed: 19153375] [Full Text: https://doi.org/10.1212/01.wnl.0000339494.76377.d6]
Grinton, B. E., Robertson, E., Fearnley, L. G., Scheffer, I. E., Marson, A. G., O'Brien, T. J., Pickrell, W. O., Rees, M. I., Sisodiya, S. M., Balding, D. J., Bennett, M. F., Bahlo, M., Berkovic, S. F., Oliver, K. L. A founder event causing a dominant childhood epilepsy survives 800 years through weak selective pressure. Am. J. Hum. Genet. 109: 2080-2087, 2022. [PubMed: 36288729] [Full Text: https://doi.org/10.1016/j.ajhg.2022.10.004]
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]
Singh, R., Scheffer, I. E., Crossland, K., Berkovic, S. F. Generalized epilepsy with febrile seizures plus: a common childhood-onset genetic epilepsy syndrome. Ann. Neurol. 45: 75-81, 1999. [PubMed: 9894880] [Full Text: https://doi.org/10.1002/1531-8249(199901)45:1<75::aid-art13>3.0.co;2-w]
Wallace, R. H., Scheffer, I. E., Parasivam, G., Barnett, S., Wallace, G. B., Sutherland, G. R., Berkovic, S. F., Mulley, J. C. Generalized epilepsy with febrile seizures plus: mutation of the sodium channel subunit SCN1B. Neurology 58: 1426-1429, 2002. [PubMed: 12011299] [Full Text: https://doi.org/10.1212/wnl.58.9.1426]
Wallace, R. H., Wang, D. W., Singh, R., Scheffer, I. E., George, A. L., Jr., Phillips, H. A., Saar, K., Reis, A., Johnson, E. W., Sutherland, G. R., Berkovic, S. F., Mulley, J. C. Febrile seizures and generalized epilepsy associated with a mutation in the Na(+)-channel beta-1 subunit gene SCN1B. Nature Genet. 19: 366-370, 1998. [PubMed: 9697698] [Full Text: https://doi.org/10.1038/1252]