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Intellectual disability

Gene: EXOC2

Amber List (moderate evidence)

EXOC2 (exocyst complex component 2)
EnsemblGeneIds (GRCh38): ENSG00000112685
EnsemblGeneIds (GRCh37): ENSG00000112685
OMIM: 615329, Gene2Phenotype
EXOC2 is in 1 panel

2 reviews

Arina Puzriakova (Genomics England Curator)

Comment on list classification: New gene added by Konstantinos Varvagiannis. Updating rating from Grey to Amber based on one publication (PMID:32639540) reporting 2 families with EXOC2 variants and variable ID, among other features. Additional cases with a significant ID phenotype are required before inclusion of this gene on a diagnostic panel.
Created: 16 Nov 2020, 2:51 p.m. | Last Modified: 16 Nov 2020, 2:51 p.m.
Panel Version: 3.537

Konstantinos Varvagiannis (Other)

I don't know

Van Bergen et al (2020 - PMID: 32639540) report on 3 individuals from 2 families, harboring biallelic EXOC2 mutations.

Clinical presentation included DD, ID (severe in 2 subjects from fam1, borderline intellectual functioning in fam2), dysmorphic features and brain abnormalities. Cerebellar anomalies were common to all with a molar tooth sign observed in one (1/3). Other findings limited to subjects from one family included acquired microcephaly, congenital contractures, spastic quadriplegia (each observed 2/3).

Previous investigations were in all cases non-diagnostic. WES identified biallelic EXOC2 mutations in all affected individuals.

EXOC2 encodes an exocyst subunit. The latter is an octameric complex, component of the membrane transport machinery, required for tethering and fusion of vesicles at the plasma membrane. As discussed ,vesicle transport is important for the development of brain and the function of neurons and glia. Exocyst function is also important for delivery of Arl13b to the primary cilium (biallelic ARL13B mutations cause Joubert syndrome 8) and ciliogenesis.

Affected subjects from a broader consanguineous family (fam1) were homozygous for a truncating variant. Fibroblast studies revealed mRNA levels compatible with NMD (further restored in presence of CHX) as well as reduced protein levels. The female belonging to the second non-consanguineous family was found to harbor 2 missense variants in trans configuration.

An exocytosis defect was demonstrated in fibroblasts from individuals belonging to both families. Ciliogenesis appeared to be normal, however Arl13b localization/recruitment to the cilia was reduced compared with control cells with the defect rescued upon exogenous expression of wt EXOC2.

Mutations in other genes encoding components of the exocyst complex have been previously reported in individuals with relevant phenotypes (e.g. EXOC8 in a boy with features of Joubert s. or EXOC4 in nephrotic syndrome).

The authors discuss on the essential role of EXOC2 based on model organism studies (e.g. impaired neuronal membrane traffic, failure of neuronal polarization and neuromuscular junction expansion seen in Drosophila Sec5 (EXOC2) null mutants).
Sources: Literature
Created: 13 Jul 2020, 6:47 p.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Global developmental delay; Intellectual disability; Abnormality of the face; Abnormality of brain morphology



Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
  • Expert Review Amber
  • Global developmental delay
  • Intellectual disability
  • Abnormality of the face
  • Abnormality of brain morphology
Clinvar variants
Variants in EXOC2
Panels with this gene

History Filter Activity

16 Nov 2020, Gel status: 2

Entity classified by Genomics England curator

Arina Puzriakova (Genomics England Curator)

Gene: exoc2 has been classified as Amber List (Moderate Evidence).

13 Jul 2020, Gel status: 0

Created, Added New Source, Set mode of inheritance, Set publications, Set Phenotypes, Set penetrance

Konstantinos Varvagiannis (Other)

gene: EXOC2 was added gene: EXOC2 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: EXOC2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: EXOC2 were set to 32639540 Phenotypes for gene: EXOC2 were set to Global developmental delay; Intellectual disability; Abnormality of the face; Abnormality of brain morphology Penetrance for gene: EXOC2 were set to Complete Review for gene: EXOC2 was set to AMBER