#615476
Table of Contents
A number sign (#) is used with this entry because of evidence that developmental and epileptic encephalopathy-18 (DEE18) is caused by homozygous or compound heterozygous mutation in the SZT2 gene (615463) on chromosome 1p34.
Developmental and epileptic encephalopathy-18 (DEE18) is a severe autosomal recessive neurologic disorder characterized by lack of psychomotor development apparent from birth, dysmorphic facial features, and early onset of refractory seizures. Brain imaging shows a thick corpus callosum and persistent cavum septum pellucidum on brain imaging (summary by Basel-Vanagaite et al., 2013).
For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.
Basel-Vanagaite et al. (2013) reported 2 unrelated children with early-onset epileptic encephalopathy. Both showed severely delayed psychomotor development with hypotonia since infancy, lack of speech, and inability to sit or stand unsupported. A 10-year-old girl, born of unrelated Iraqi Jewish parents, first developed intractable seizures at age 4 years. Seizures were characterized by loss of consciousness, drooling, and perioral cyanosis, and sometimes followed by tonic-clonic generalized seizures. One of her brothers likely had the same condition; he had profound developmental delay and intractable seizures, and died at age 3 years from respiratory infection. The second child, a 9-year-old Spanish boy, developed intractable tonic and absence seizures at age 2 months. EEG in both patients showed abnormal background trace and prominent epileptiform abnormalities, but no suppression burst pattern. Both probands had common facial dysmorphic features, including high forehead, downslanting palpebral fissures, ptosis, and arched, laterally extended eyebrows. Brain MRI in both patients and in the deceased sib of the first patient showed short and thick corpus callosum and persistent cavum septum pellucidum.
Tsuchida et al. (2018) reported 3 patients with DEE18. Patient 1 was a 4-year-old Japanese girl with onset of intractable seizures at age 2 months, including complex partial seizures with tonic generalization. She also had hypotonia and severely impaired intellectual development with lack of speech. Brain MRI at age 2 years showed a short and thick corpus callosum. Patient 2 was a 2-year-old Japanese boy with onset of intractable partial seizures at age 3 months. He also had hypotonia, chorea, and severely impaired intellectual development with lack of speech. Brain MRI at age 18 months showed a cavum septum pellucidum and mildly dilated ventricles. Patient 3 was a 5-year-old Malaysian girl with onset of tonic spasms at age 8 months. She also had hypotonia, clonus, and severely impaired intellectual development with lack of speech. Brain MRI at age 20 months showed a thin corpus callosum and dilated lateral and third ventricles.
Imaizumi et al. (2018) reported a 15-year-old boy with DEE18. He had delayed development and walked at age 2 years. At age 4.5 years, he was noted to have macrocephaly, and he developed seizures at age 10 years. At age 15 years, he had autistic features and no speech. His macrocephaly had normalized and he had no dysmorphic features other than a tall forehead.
Kariminejad et al. (2019) reported a patient with a history of developmental delays, no speech, and 3 tonic clonic seizures. He was also described as having autistic features. He had dysmorphisms including a prominent forehead and sandal gap between his first and second toes. A brain MRI was normal.
Iodice et al. (2019) reported a Ukrainian girl with severe hypotonia and psychomotor delay from the first year of life. At age 30 months, she developed focal clonic seizures that evolved into right temporal status epilepticus and were associated with psychomotor regression. Her clinical symptoms progressed to epileptic encephalopathy with a Lennox-Gastaut-like pattern on EEG. Brain MRI showed a short and thick corpus callosum and hippocampal atrophy. At age 6 years, she had rare seizures that mostly occurred during sleep, macrocephaly, severe axial hypotonia, global developmental delay, and absent speech.
Trivisano et al. (2020) reported 2 Italian sisters, aged 11 and 6 years, who had normal development before epilepsy onset between 5 and 6 months of age. One sister had rare seizures, which were controlled with antiepileptic medication, whereas the other had monthly seizures, which often evolved into status epilepticus and were resistant to antiepileptic medications. Both sibs had mildly to moderately impaired intellectual development and behavioral disturbances. They also had dysmorphisms including macrocephaly, prominent forehead, downslanting palpebral fissures, and ptosis. Brain MRI in both sibs showed a thin corpus callosum with an abnormal splenium shape.
The transmission pattern of DEE18 in the families reported by Basel-Vanagaite et al. (2013) was consistent with autosomal recessive inheritance.
In 2 unrelated patients with DEE18, Basel-Vanagaite et al. (2013) identified biallelic truncating mutations in the SZT2 gene (615463.0001-615463.0003). The mutations were found by whole-exome sequencing and segregated with the disorder in the families. The presence of severe developmental delay before the onset of epilepsy in 1 patient suggested that SZT2 mutations also impair brain maturation independently of seizures.
Tsuchida et al. (2018) identified 6 novel compound heterozygous mutations (615463.0005-615463.0010) in the SZT2 gene in 3 children with DEE18. The mutations included 3 truncating, 1 splice site, and 2 missense mutations. The mutations were identified by whole-exome sequencing, and all of the parents were shown to be mutation carriers.
In a 15-year-old boy with DEE18, Imaizumi et al. (2018) identified a homozygous missense mutation in the SZT2 gene (R2185W; 615463.0011). The mutation was identified by whole-exome sequencing. Microarray analysis showed that the patient had paternal uniparental disomy of chromosome 1.
In an Iranian boy, born to consanguineous parents, with DEE18, Kariminejad et al. (2019) identified a homozygous missense mutation in the SZT2 gene (C2481Y; 615463.0012). The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing. The parents were confirmed to be carriers.
In 2 Italian sisters, born to consanguineous parents, with DEE18, Trivisano et al. (2020) identified a homozygous missense mutation in the SZT2 gene (W2609G; 615463.0013). The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing.
Frankel et al. (2009) found that mutation in the Szt2 gene in mice increased seizure threshold and epileptogenesis.
Basel-Vanagaite, L., Hershkovitz, T., Heyman, E., Raspall-Chaure, M., Kakar, N., Smirin-Yosef, P., Vila-Pueyo, M., Kornreich, L., Thiele, H., Bode, H., Lagovsky, I., Dahary, D., and 9 others. Biallelic SZT2 mutations cause infantile encephalopathy with epilepsy and dysmorphic corpus callosum. Am. J. Hum. Genet. 93: 524-529, 2013. [PubMed: 23932106, images, related citations] [Full Text]
Frankel, W. N., Yang, Y., Mahaffey, C. L., Beyer, B. J., O'Brien, T. P. Szt2, a novel gene for seizure threshold in mice. Genes Brain Behav. 8: 568-576, 2009. [PubMed: 19624305, images, related citations] [Full Text]
Imaizumi, T., Kumakura, A., Yamamoti-Shimojima, K., Ondo, Y., Yamamoto, T. Identification of a rare homozygous SZT2 variant due to uniparental disomy in a patient with neurodevelopmental disorder. Intractable Rare Dis. Res. 7: 245-250, 2018. [PubMed: 30560016, related citations] [Full Text]
Iodice, A., Spagnoli, C., Frattini, D., Salerno, G. G., Rizzi, S., Fusco, C. Biallelic SZT2 mutation with early onset of focal status epilepticus: useful diagnostic clues other than epilepsy, intellectual disability and macrocephaly. (Letter) Seizure 69: 296-297, 2019. [PubMed: 31146092, related citations] [Full Text]
Kariminejad, A., Yazdan, H., Rahimian, E., Kalhor, Z., Fattahi, Z., Zonooz, M. F., Najmabadi, H., Ashrafi, M. SZT2 mutation in a boy with intellectual disability, seizures and autistic features. Europ. J. Med. Genet. 62: 103556, 2019. Note: Electronic Article. [PubMed: 30359774, related citations] [Full Text]
Trivisano, M., Rivera, M., Terracciano, A., Ciolfi, A., Napolitano, A., Pepi, C., Calabrese, C., Digilio, M. C., Tartaglia, M., Curatolo, P., Vigevano, F., Specchio, N. Developmental and epileptic encephalopathy due to SZT2 genomic variants: emerging features of a syndromic condition. Epilepsy Behav. 108: 107097, 2020. Note: Electronic Article. [PubMed: 32402703, related citations] [Full Text]
Tsuchida, N., Nakashima, M., Miyauchi, A., Yoshitomi, S., Kimizu, T., Ganesan, V., Teik, K. W., Ch'ng, G. S., Kato, M., Mizuguchi, T., Takata, A., Miyatake, S., Miyake, N., Osaka, H., Yamagata, T., Nakajima, H., Saitsu, H., Matsumoto, N. Novel biallelic SZT2 mutations in 3 cases of early-onset epileptic encephalopathy. Clin. Genet. 93: 266-274, 2018. [PubMed: 28556953, related citations] [Full Text]
Alternative titles; symbols
ORPHA: 442835; DO: 0080413;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 1p34.2 | Developmental and epileptic encephalopathy 18 | 615476 | Autosomal recessive | 3 | SZT2 | 615463 |
A number sign (#) is used with this entry because of evidence that developmental and epileptic encephalopathy-18 (DEE18) is caused by homozygous or compound heterozygous mutation in the SZT2 gene (615463) on chromosome 1p34.
Developmental and epileptic encephalopathy-18 (DEE18) is a severe autosomal recessive neurologic disorder characterized by lack of psychomotor development apparent from birth, dysmorphic facial features, and early onset of refractory seizures. Brain imaging shows a thick corpus callosum and persistent cavum septum pellucidum on brain imaging (summary by Basel-Vanagaite et al., 2013).
For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.
Basel-Vanagaite et al. (2013) reported 2 unrelated children with early-onset epileptic encephalopathy. Both showed severely delayed psychomotor development with hypotonia since infancy, lack of speech, and inability to sit or stand unsupported. A 10-year-old girl, born of unrelated Iraqi Jewish parents, first developed intractable seizures at age 4 years. Seizures were characterized by loss of consciousness, drooling, and perioral cyanosis, and sometimes followed by tonic-clonic generalized seizures. One of her brothers likely had the same condition; he had profound developmental delay and intractable seizures, and died at age 3 years from respiratory infection. The second child, a 9-year-old Spanish boy, developed intractable tonic and absence seizures at age 2 months. EEG in both patients showed abnormal background trace and prominent epileptiform abnormalities, but no suppression burst pattern. Both probands had common facial dysmorphic features, including high forehead, downslanting palpebral fissures, ptosis, and arched, laterally extended eyebrows. Brain MRI in both patients and in the deceased sib of the first patient showed short and thick corpus callosum and persistent cavum septum pellucidum.
Tsuchida et al. (2018) reported 3 patients with DEE18. Patient 1 was a 4-year-old Japanese girl with onset of intractable seizures at age 2 months, including complex partial seizures with tonic generalization. She also had hypotonia and severely impaired intellectual development with lack of speech. Brain MRI at age 2 years showed a short and thick corpus callosum. Patient 2 was a 2-year-old Japanese boy with onset of intractable partial seizures at age 3 months. He also had hypotonia, chorea, and severely impaired intellectual development with lack of speech. Brain MRI at age 18 months showed a cavum septum pellucidum and mildly dilated ventricles. Patient 3 was a 5-year-old Malaysian girl with onset of tonic spasms at age 8 months. She also had hypotonia, clonus, and severely impaired intellectual development with lack of speech. Brain MRI at age 20 months showed a thin corpus callosum and dilated lateral and third ventricles.
Imaizumi et al. (2018) reported a 15-year-old boy with DEE18. He had delayed development and walked at age 2 years. At age 4.5 years, he was noted to have macrocephaly, and he developed seizures at age 10 years. At age 15 years, he had autistic features and no speech. His macrocephaly had normalized and he had no dysmorphic features other than a tall forehead.
Kariminejad et al. (2019) reported a patient with a history of developmental delays, no speech, and 3 tonic clonic seizures. He was also described as having autistic features. He had dysmorphisms including a prominent forehead and sandal gap between his first and second toes. A brain MRI was normal.
Iodice et al. (2019) reported a Ukrainian girl with severe hypotonia and psychomotor delay from the first year of life. At age 30 months, she developed focal clonic seizures that evolved into right temporal status epilepticus and were associated with psychomotor regression. Her clinical symptoms progressed to epileptic encephalopathy with a Lennox-Gastaut-like pattern on EEG. Brain MRI showed a short and thick corpus callosum and hippocampal atrophy. At age 6 years, she had rare seizures that mostly occurred during sleep, macrocephaly, severe axial hypotonia, global developmental delay, and absent speech.
Trivisano et al. (2020) reported 2 Italian sisters, aged 11 and 6 years, who had normal development before epilepsy onset between 5 and 6 months of age. One sister had rare seizures, which were controlled with antiepileptic medication, whereas the other had monthly seizures, which often evolved into status epilepticus and were resistant to antiepileptic medications. Both sibs had mildly to moderately impaired intellectual development and behavioral disturbances. They also had dysmorphisms including macrocephaly, prominent forehead, downslanting palpebral fissures, and ptosis. Brain MRI in both sibs showed a thin corpus callosum with an abnormal splenium shape.
The transmission pattern of DEE18 in the families reported by Basel-Vanagaite et al. (2013) was consistent with autosomal recessive inheritance.
In 2 unrelated patients with DEE18, Basel-Vanagaite et al. (2013) identified biallelic truncating mutations in the SZT2 gene (615463.0001-615463.0003). The mutations were found by whole-exome sequencing and segregated with the disorder in the families. The presence of severe developmental delay before the onset of epilepsy in 1 patient suggested that SZT2 mutations also impair brain maturation independently of seizures.
Tsuchida et al. (2018) identified 6 novel compound heterozygous mutations (615463.0005-615463.0010) in the SZT2 gene in 3 children with DEE18. The mutations included 3 truncating, 1 splice site, and 2 missense mutations. The mutations were identified by whole-exome sequencing, and all of the parents were shown to be mutation carriers.
In a 15-year-old boy with DEE18, Imaizumi et al. (2018) identified a homozygous missense mutation in the SZT2 gene (R2185W; 615463.0011). The mutation was identified by whole-exome sequencing. Microarray analysis showed that the patient had paternal uniparental disomy of chromosome 1.
In an Iranian boy, born to consanguineous parents, with DEE18, Kariminejad et al. (2019) identified a homozygous missense mutation in the SZT2 gene (C2481Y; 615463.0012). The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing. The parents were confirmed to be carriers.
In 2 Italian sisters, born to consanguineous parents, with DEE18, Trivisano et al. (2020) identified a homozygous missense mutation in the SZT2 gene (W2609G; 615463.0013). The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing.
Frankel et al. (2009) found that mutation in the Szt2 gene in mice increased seizure threshold and epileptogenesis.
Basel-Vanagaite, L., Hershkovitz, T., Heyman, E., Raspall-Chaure, M., Kakar, N., Smirin-Yosef, P., Vila-Pueyo, M., Kornreich, L., Thiele, H., Bode, H., Lagovsky, I., Dahary, D., and 9 others. Biallelic SZT2 mutations cause infantile encephalopathy with epilepsy and dysmorphic corpus callosum. Am. J. Hum. Genet. 93: 524-529, 2013. [PubMed: 23932106] [Full Text: https://doi.org/10.1016/j.ajhg.2013.07.005]
Frankel, W. N., Yang, Y., Mahaffey, C. L., Beyer, B. J., O'Brien, T. P. Szt2, a novel gene for seizure threshold in mice. Genes Brain Behav. 8: 568-576, 2009. [PubMed: 19624305] [Full Text: https://doi.org/10.1111/j.1601-183X.2009.00509.x]
Imaizumi, T., Kumakura, A., Yamamoti-Shimojima, K., Ondo, Y., Yamamoto, T. Identification of a rare homozygous SZT2 variant due to uniparental disomy in a patient with neurodevelopmental disorder. Intractable Rare Dis. Res. 7: 245-250, 2018. [PubMed: 30560016] [Full Text: https://doi.org/10.5582/irdr.2018.01117]
Iodice, A., Spagnoli, C., Frattini, D., Salerno, G. G., Rizzi, S., Fusco, C. Biallelic SZT2 mutation with early onset of focal status epilepticus: useful diagnostic clues other than epilepsy, intellectual disability and macrocephaly. (Letter) Seizure 69: 296-297, 2019. [PubMed: 31146092] [Full Text: https://doi.org/10.1016/j.seizure.2019.05.015]
Kariminejad, A., Yazdan, H., Rahimian, E., Kalhor, Z., Fattahi, Z., Zonooz, M. F., Najmabadi, H., Ashrafi, M. SZT2 mutation in a boy with intellectual disability, seizures and autistic features. Europ. J. Med. Genet. 62: 103556, 2019. Note: Electronic Article. [PubMed: 30359774] [Full Text: https://doi.org/10.1016/j.ejmg.2018.10.008]
Trivisano, M., Rivera, M., Terracciano, A., Ciolfi, A., Napolitano, A., Pepi, C., Calabrese, C., Digilio, M. C., Tartaglia, M., Curatolo, P., Vigevano, F., Specchio, N. Developmental and epileptic encephalopathy due to SZT2 genomic variants: emerging features of a syndromic condition. Epilepsy Behav. 108: 107097, 2020. Note: Electronic Article. [PubMed: 32402703] [Full Text: https://doi.org/10.1016/j.yebeh.2020.107097]
Tsuchida, N., Nakashima, M., Miyauchi, A., Yoshitomi, S., Kimizu, T., Ganesan, V., Teik, K. W., Ch'ng, G. S., Kato, M., Mizuguchi, T., Takata, A., Miyatake, S., Miyake, N., Osaka, H., Yamagata, T., Nakajima, H., Saitsu, H., Matsumoto, N. Novel biallelic SZT2 mutations in 3 cases of early-onset epileptic encephalopathy. Clin. Genet. 93: 266-274, 2018. [PubMed: 28556953] [Full Text: https://doi.org/10.1111/cge.13061]
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