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Intellectual disability v9.185 BSN Ida Ertmanska changed review comment from: Literature review by Helen Lord (Oxford Medical Genetics Laboratories) copied from the Epilepsy panel:

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
Sources: Other; to: Literature review by Helen Lord (Oxford Medical Genetics Laboratories) copied from the Epilepsy panel:

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.
Intellectual disability v9.185 BSN Ida Ertmanska gene: BSN was added
gene: BSN was added to Intellectual disability. Sources: Other
Mode of inheritance for gene: BSN was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: BSN were set to 36600631; 39616287; 40393460
Phenotypes for gene: BSN were set to neurodevelopmental disorder, MONDO:0700092
Review for gene: BSN was set to GREEN
Added comment: Literature review by Helen Lord (Oxford Medical Genetics Laboratories) copied from the Epilepsy panel:

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
Sources: Other
Intellectual disability v9.144 MED12L Eleanor Williams changed review comment from: Since the last review additional cases have been reported.
In OMIM this gene is associated with Nizon-Isidor syndrome, OMIM:618872 (AD) - accessed 21st October 2025
In ClinGen the gene has a definitive rating with Nizon-Isidor syndrome, MONDO:0030030

There are now 3 more reports of plausable pathogenic variants in this gene in patients with an intellectual disability phenotype. 2 cases with de novo variants and 1 with a maternally inherited variant.

PMID: 36212160 - Park et al 2022 - WES to analyse 1,180 Korean patients with neurological symptoms. 1 individual with a de novo variant c.1895C>T; p.Ser632Leu in MED12L and a phenotype of global developmental delay and facial dysmorphism.

PMID: 35920825 - Ferraz et al 2022 - a male proband with a confirmed de novo germline frameshift variant in MED12L (NM_053002.6 (MED12L_v001):c.971del;p.(pro324Glnfs∗18)) identified by WES. The clinical phenotype included mild motor and speech delay, oligodontia, and dysmorphic signs. Of note the patient also carried 2 de novo chromosomal balanced reciprocal translocations: 46,XY,t(1;2)(p33;p22),t(5;9)(p15;q21) and the authors note that Nizon et al. 2019 report a patient with a balanced reciprocal translocation suggesting that the MED12L loss-of-function variant may contribute to chromosomal instability.

PMID: 40957966 - Dutta et al 2025 - report a proband with likely pathogenic MED12L nonsense variant (p.Arg1210Ter) which is maternally inherited (father also sequenced). At 2.5 yo the proband was diagnosed with global developmental delay, absent speech, ASD, hyperactivity, exophoria and myopia. Developmental regression began between 18 - 24 months. She has frequent respiratory infections. The 19 yo mother has a clinical history which includes speech delay and learning disability, but features are much milder than the proband. The proband also has inherited a pathogenic GAMT variant from her mother and a pathogenic TNFRSF13B variant from her father but these are not thought to contribute to the ID phenotype.; to: Since the last review additional cases have been reported.
In OMIM this gene is associated with Nizon-Isidor syndrome, OMIM:618872 (AD) - accessed 21st October 2025
In ClinGen the gene has a definitive rating with Nizon-Isidor syndrome, MONDO:0030030 (last curated November 19th, 2024)

There are now 3 more reports of plausable pathogenic variants in this gene in patients with an intellectual disability phenotype. 2 cases with de novo variants and 1 with a maternally inherited variant.

PMID: 36212160 - Park et al 2022 - WES to analyse 1,180 Korean patients with neurological symptoms. 1 individual with a de novo variant c.1895C>T; p.Ser632Leu in MED12L and a phenotype of global developmental delay and facial dysmorphism.

PMID: 35920825 - Ferraz et al 2022 - a male proband with a confirmed de novo germline frameshift variant in MED12L (NM_053002.6 (MED12L_v001):c.971del;p.(pro324Glnfs∗18)) identified by WES. The clinical phenotype included mild motor and speech delay, oligodontia, and dysmorphic signs. Of note the patient also carried 2 de novo chromosomal balanced reciprocal translocations: 46,XY,t(1;2)(p33;p22),t(5;9)(p15;q21) and the authors note that Nizon et al. 2019 report a patient with a balanced reciprocal translocation suggesting that the MED12L loss-of-function variant may contribute to chromosomal instability.

PMID: 40957966 - Dutta et al 2025 - report a proband with likely pathogenic MED12L nonsense variant (p.Arg1210Ter) which is maternally inherited (father also sequenced). At 2.5 yo the proband was diagnosed with global developmental delay, absent speech, ASD, hyperactivity, exophoria and myopia. Developmental regression began between 18 - 24 months. She has frequent respiratory infections. The 19 yo mother has a clinical history which includes speech delay and learning disability, but features are much milder than the proband. The proband also has inherited a pathogenic GAMT variant from her mother and a pathogenic TNFRSF13B variant from her father but these are not thought to contribute to the ID phenotype.
Intellectual disability v9.141 MED12L Eleanor Williams edited their review of gene: MED12L: Added comment: Since the last review additional cases have been reported.
In OMIM this gene is associated with Nizon-Isidor syndrome, OMIM:618872 (AD) - accessed 21st October 2025
In ClinGen the gene has a definitive rating with Nizon-Isidor syndrome, MONDO:0030030

There are now 3 more reports of plausable pathogenic variants in this gene in patients with an intellectual disability phenotype. 2 cases with de novo variants and 1 with a maternally inherited variant.

PMID: 36212160 - Park et al 2022 - WES to analyse 1,180 Korean patients with neurological symptoms. 1 individual with a de novo variant c.1895C>T; p.Ser632Leu in MED12L and a phenotype of global developmental delay and facial dysmorphism.

PMID: 35920825 - Ferraz et al 2022 - a male proband with a confirmed de novo germline frameshift variant in MED12L (NM_053002.6 (MED12L_v001):c.971del;p.(pro324Glnfs∗18)) identified by WES. The clinical phenotype included mild motor and speech delay, oligodontia, and dysmorphic signs. Of note the patient also carried 2 de novo chromosomal balanced reciprocal translocations: 46,XY,t(1;2)(p33;p22),t(5;9)(p15;q21) and the authors note that Nizon et al. 2019 report a patient with a balanced reciprocal translocation suggesting that the MED12L loss-of-function variant may contribute to chromosomal instability.

PMID: 40957966 - Dutta et al 2025 - report a proband with likely pathogenic MED12L nonsense variant (p.Arg1210Ter) which is maternally inherited (father also sequenced). At 2.5 yo the proband was diagnosed with global developmental delay, absent speech, ASD, hyperactivity, exophoria and myopia. Developmental regression began between 18 - 24 months. She has frequent respiratory infections. The 19 yo mother has a clinical history which includes speech delay and learning disability, but features are much milder than the proband. The proband also has inherited a pathogenic GAMT variant from her mother and a pathogenic TNFRSF13B variant from her father but these are not thought to contribute to the ID phenotype.; Changed rating: GREEN; Changed publications to: 31155615, 36212160, 35920825, 40957966; Changed phenotypes to: Nizon-Isidor syndrome, OMIM:618872, Nizon-Isidor syndrome, MONDO:0030030; Changed mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Intellectual disability v3.200 ADAMTS10 Arina Puzriakova edited their review of gene: ADAMTS10: Changed publications: 15368195, 18567016, 19836009, 25469541
Intellectual disability v3.200 ADAMTS10 Arina Puzriakova Classified gene: ADAMTS10 as Amber List (moderate evidence)
Intellectual disability v3.200 ADAMTS10 Arina Puzriakova Added comment: Comment on list classification: While mild ID is reportedly a phenotypic feature associated with Weill–Marchesani syndrome, this is not evident in the literature cases. Therefore, a more consistent and/or significant pattern of ID is necessary for inclusion of ADAMTS10 on a diagnostic ID panel.
Intellectual disability v3.200 ADAMTS10 Arina Puzriakova Gene: adamts10 has been classified as Amber List (Moderate Evidence).
Intellectual disability v3.199 ADAMTS10 Arina Puzriakova reviewed gene: ADAMTS10: Rating: AMBER; Mode of pathogenicity: None; Publications: 15368195, 18567016, 19836009; Phenotypes: Weill-Marchesani syndrome, 277600; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Intellectual disability v3.0 ADAMTS10 Zornitza Stark gene: ADAMTS10 was added
gene: ADAMTS10 was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: ADAMTS10 was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: ADAMTS10 were set to Weill-Marchesani syndrome 1, recessive, MIM#277600
Review for gene: ADAMTS10 was set to AMBER
Added comment: Mild intellectual disability is described in around 10% of affected individuals.
Sources: Expert list
Intellectual disability v2.468 GAMT Louise Daugherty Source Victorian Clinical Genetics Services was added to GAMT.
Intellectual disability v2.468 CAMTA1 Louise Daugherty Source Victorian Clinical Genetics Services was added to CAMTA1.
Intellectual disability GAMT BRIDGE consortium edited their review of GAMT
Intellectual disability CAMTA1 BRIDGE consortium edited their review of CAMTA1
Intellectual disability AMT BRIDGE consortium edited their review of AMT
Intellectual disability GAMT BRIDGE consortium edited their review of GAMT
Intellectual disability CAMTA1 BRIDGE consortium edited their review of CAMTA1
Intellectual disability AMT BRIDGE consortium edited their review of AMT
Intellectual disability GAMT BRIDGE consortium reviewed GAMT
Intellectual disability CAMTA1 BRIDGE consortium reviewed CAMTA1
Intellectual disability AMT BRIDGE consortium reviewed AMT