Genetic epilepsy syndromesGene: CUL3
Comment on list classification: Rating Amber based on external expert review and evidence provided by Konstantinos Varvagiannis. Only two unrelated cases reported and therefore not yet reaching threshold for inclusion.
Created: 2 Oct 2020, 10:34 a.m. | Last Modified: 2 Oct 2020, 10:34 a.m.
Panel Version: 2.155
Epilepsy has been reported in at least 2 relevant individuals in the literature.
Nakashima et al (2020 - PMID:32341456) provide clinical details on 3 unrelated individuals with de novo CUL3 variants.
Features included DD, variable degrees of ID (P1: severe, P3: mild, P2: NA although he displayed motor and severe speech and language delay and had severe learning difficulties). Two out of three had intractable seizures (onset 2 - 6 months). One presented with congenital heart defects (ASD, PV stenosis) and another submucosal palatoschisis/bifid uvula. There were no facial dysmorphisms reported.
CUL3 encodes Cullin-3, a core piece of the E3 ubiquitin ligase complex, thus playing a role in the ubiquitin-proteasome system. [ https://ghr.nlm.nih.gov/gene/CUL3 ]. Germline variants in some other Cullin family genes (eg. CUL4B, CUL7) cause disorders with ID as a feature.
The 3 individuals reported by Nakashima had variable previous investigations (karyotype, CMA, metabolic testing) which were non-diagnostic. Singleton or trio exome sequencing identified 2 frameshift and 1 missense variant (NM_003590.4:c.854T>C / p.Val285Ala), further confirmed with Sanger sequencing. De novo occurrence was confirmed by analysis of microsatellite markers in an individual with singleton ES.
While the frameshift variants were presumed to lead to NMD (not studied), studies in HEK293T cells suggested that the Val285Ala reduced binding ability with KEAP1, possibly leading to instability of the Cullin-RING ligase (CRL) complex and impairment of the ubiquitin-proteasome system.
In OMIM, the phenotype associated with heterozygous CUL3 mutations is Pseudohypoaldosteronism type IIE (PHA2E - # 614496). As OMIM and Nakashima et al comment, PHA2E-associated variants are clustered around exon 9, most lead to skipping of exon 9 and produce an in-frame deletion of 57 aa in the cullin homology domain. Few (probably 3) missense variants in exon 9 have also been reported. Individuals with PHA2E do not display DD/ID and conversely individuals with NDD did not display features of PHA2E.
Nakashima et al summarize the phenotypes associated with 12 further de novo CUL3 variants in the literature with most pLOF ones detected in individuals with autism and/or developmental disorders and in few cases with congenital heart disease. Few additional missense variants and a stoploss one have been reported in individuals with NDD and one in SCZ.
Heterozygous Cul3 (/tissue-specific) deletion in mice resulted in autism-like behavior. Cul3 deficient mice also demonstrated NMDAR hypofunction and decreased spine density. [PMIDs cited : 31455858, 31780330]
Overall haploinsufficiency is favored as the underlying mechanism of variants associated with NDD. Nakashima et al comment that the pathogenesis of missense variants remains unknown and/or that a dominant-negative effect on CRL may be possible.
Studies on larger cohorts reporting on individuals with relevant phenotypes due to de novo CUL3 variants (eg. DDD study - PMID: 28135719, Lelieveld et al - PMID: 27479843), are better summarized in denovo-db (after filtering for coding variants):
Please consider inclusion in other panels if appropriate (e.g. for ASD).
Created: 8 May 2020, 9:46 a.m.
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Global developmental delay; Intellectual disability; Seizures; Abnormality of cardiovascular system morphology; Abnormality of the palate; Pseudohypoaldosteronism, type IIE - MIM #614496
Gene: cul3 has been classified as Amber List (Moderate Evidence).
gene: CUL3 was added gene: CUL3 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: CUL3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: CUL3 were set to 32341456 Phenotypes for gene: CUL3 were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of cardiovascular system morphology; Abnormality of the palate; Pseudohypoaldosteronism, type IIE - MIM #614496 Penetrance for gene: CUL3 were set to unknown Review for gene: CUL3 was set to AMBER