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Early onset or syndromic epilepsy v8.61 BSN Helen Lord gene: BSN was added
gene: BSN was added to Early onset or syndromic epilepsy. Sources: Other
Mode of inheritance for gene: BSN was set to Unknown
Publications for gene: BSN were set to PMID: 36600631; 39616287; 40393460
Phenotypes for gene: BSN were set to Seizures - different types
Penetrance for gene: BSN were set to unknown
Review for gene: BSN was set to AMBER
Added comment: There are a lot of cases to support an AD phenotype but unsure as to whether there is also an AR pheontype associated with disease...

PMID:36600631 - Ye et al, 2023:
BSN gene encodes the Bsssoon protein which is highly expressed in the mammalian brain especially the cerebral cortex and the hippocampus.
WES in 313 trios with epilepsies of unknown causes novel BSN variants identifed in 5 cases and 3 additional variants identified in 3 cases from different centres:
Cases 1-4 compound het - variants shown to be inherited in trans
Cases 5-8 - het variants idenitied in case 5 & 6 inherited from affected parent (febrile seizure in these parents) and in cases 7 & 8 - arise de novo.
The 9 variants present in low or no allele freq in all populations or East Asian populations - no hom in gnomAD. No other pathogenic/likely pathogenic variants in other epilepsy genes identiifed.
Fig 3:
B:The 2 nonsense variants in exon 5 thought to result in the truncation of the basson protein and trigger NMD. Both de novo. They state LOF and haploinsuffucency of BSN are potentially pathogenic.
C: 6/9 missense variants led to hydrogen bond alterations - mostly creation of hydrogen bonds which were not predicted orignally. 5/9 missense variants clustered in the C-terminus. Among the 4 pairs of compound het variants at least 1 variant in each pair had hydrogen bond alterations.
In the discussion they state LOF of Bassoon is potentially the underlying mechanism of pathogenicity of BSN variants, which is consistent with the pathogenisi of other genes encoding CAZ proteins such as UNC13A and UNC13B; however, the functional effects of BSN variants warrants further investigation.
In het BSN knockout mice - no phenotype; however, hom knockout mice null led to spontaneous seizures and partial preamture lethality. Clinically the patients with monoallelic BSN missense variants achieved seizure free status without treatment or under monotherapy; whereas, the majority of patients with biallelic missense variants required combination therapy, possible correlation between genotype and phenotype severity.

PMID 39616287: Yacoub et al, 2025: WES in 10 JME (juvenille myoclonic epilepsy) patients - P4 found to have a het BSN missense variant - c.2534G>A p.(Arg845Gln), also identified in her affected brother who has GTCs, but also detected in an unaffected brother. Presumably also inherited from an unaffected pedogree (pedigree included - no mention of parental testing).

PMID: 40393460 Guzman et al, 2025: cohort of 29 individuals with BSN variants including 14 with de novo vairants, 13 individuals with PTVs (protein truncating variants) of unknown inheritance and 2 individuals with PTVs with paternal inheritance. Affected individuals had diverse neurodevelopmental phenotypes including behavioural abnormalities; delayed speech, learning difficulties and variable seizure types.
Recruitment: 2/29 - enrolled in the Epilepsy genetics research project at Childrens Hospital Philadelphia (CHOP) confirmed de novo; 14/29 identified via gene matcher - 9/14 confirmed de novo by respective institutions; 7/29 identified through Penn medicine biobank; 1/29 missense de novo BSN variant identified from birth defects biorepositary at CHOP; 3/29 BSN PTVs idenitifed through the center for applied genomics at CHOP and a lit review identified 2/29 previously reported individuals with de novo PTVs in BSN.
Table 1 details the 14 individuals with de novo BSN variants - 8/14 had seizures (different types); 12/14 had developmental features.
They suggest haploinsuffucency as as a likely mechanism.
Sources: Other
Early onset or syndromic epilepsy v4.28 UNC13B Achchuthan Shanmugasundram Phenotypes for gene: UNC13B were changed from partial epilepsy, MONDO:0005384 to partial epilepsy, MONDO:0005384
Early onset or syndromic epilepsy v4.28 UNC13B Achchuthan Shanmugasundram Phenotypes for gene: UNC13B were changed from Epilepsy to partial epilepsy, MONDO:0005384
Early onset or syndromic epilepsy v4.27 UNC13B Achchuthan Shanmugasundram Publications for gene: UNC13B were set to 33876820; 35380625
Early onset or syndromic epilepsy v4.27 UNC13B Achchuthan Shanmugasundram Publications for gene: UNC13B were set to 33876820; 35380625
Early onset or syndromic epilepsy v4.27 UNC13B Achchuthan Shanmugasundram Publications for gene: UNC13B were set to 33876820
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Classified gene: UNC13B as Red List (low evidence)
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Gene: unc13b has been classified as Red List (Low Evidence).
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Classified gene: UNC13B as Red List (low evidence)
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Gene: unc13b has been classified as Red List (Low Evidence).
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Classified gene: UNC13B as Red List (low evidence)
Early onset or syndromic epilepsy v4.26 UNC13B Achchuthan Shanmugasundram Gene: unc13b has been classified as Red List (Low Evidence).
Early onset or syndromic epilepsy v4.25 UNC13B Achchuthan Shanmugasundram reviewed gene: UNC13B: Rating: RED; Mode of pathogenicity: None; Publications: 33876820, 35380625; Phenotypes: partial epilepsy, MONDO:0005384; Mode of inheritance: None
Early onset or syndromic epilepsy v2.435 UNC13B Zornitza Stark gene: UNC13B was added
gene: UNC13B was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: UNC13B was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: UNC13B were set to 33876820
Phenotypes for gene: UNC13B were set to Epilepsy
Review for gene: UNC13B was set to RED
Added comment: No OMIM human disease association. Gene encodes a presynaptic protein Munc13-2 highly expressed in the brain (predominantly cerebral cortex).

Variant interpretation data in human epilepsy cohort somewhat conflicting and restricted to a single study. Wang et al, Brain, 2021 - trio-based whole-exome sequencing identified UNC13B in 12 individuals affected by partial epilepsy and/or febrile seizures from 8 unrelated families. Identified:
x1 de novo nonsense variant, absent in gnomad, damaging in silicos
x1 de novo splice site, absent in gnomad, damaging in silicos
x1 splice site variant present in unaffected mother (low frequency in gnomad)
x2 compound het in one individual - more severe phenotype postulated (x1 variant present in contro cohortl, the other variant present in low frequency in gnomad)
x1 missense variant - in Han Chinese major depressive disorders study, not in gnomad
x1 missense variant - highly conserved residue, not in gnomad
x2 other missense variant - highly conserved residue, low frequency in gnomad
Latter 4 missense variants cosegregated with affected individuals in the families

In Drosophila, seizure rate and duration were increased by Unc13b knockdown compared to wild-type flies, but these effects were less pronounced than in sodium voltage-gated channel alpha subunit 1 (Scn1a) knockdown Drosophila

De novo UNC13B variants previously reported in bipolar disorder and autism spectrum disorder
Sources: Literature