Component of Oligomeric Golgi Complex 5

Alternative Names

  • COG5
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OMIM Number

606821

Gene Map Locus
7q22.3

Description

The COG5 gene encodes a protein that forms a part of the Conserved Oligomeric Golgi (COG) complex. This complex, located in the Golgi apparatus, is essential for normal Golgi morphology and function, namely protein modifications such as glycosylation. The complex is specifically involved in the intra-Golgi and ER to Golgi vesicle-mediated transport of proteins, particularly the enzymes responsible for glycosylation. It carries out this function by controlling the tethering of vesicles to the Golgi membrane. 

Mutations in the gene can thus have strong pathological consequences. The gene is associated with Congenital Disorder of Glycosylation, Type IIi (CDG2I), a disorder characterized by developmental delay, intellectual disability, brain atrophy, truncal ataxia and hypotonia.   

Molecular Genetics

The COG5 gene is located on the long arm of chromosome 7. It spans a length of 362.9 kb and consists of 23 exons. The protein encoded by this gene has a molecular mass of 92 kDa and is made up of 839 amino acids. Multiple isoforms of the COG5 protein exist due to alternative splicing and the gene is found to be overexpressed in the bone. At least 8 mutations in the COG5 gene have been identified to result in CDG2I. The homozygous intronic transition 1669-15T-C results in altered splicing and a transcript lacking the 58 amino acids of exons 15 and 16.   

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Anazi et al. (2016) aimed to compare the diagnostic yield of genomic tools with standard clinical evaluations in a cohort of 337 Intellectual Disability (ID) patients. The authors carried out molecular karyotyping, exome sequencing and sequencing by a neurological gene panel. Genomic tools were found to have a higher diagnostic yield than standard clinical evaluations (58% vs 16%). In one patient, the genomic approach uncovered a homozygous c.1120-12T>A intronic mutation in the COG5 gene. Although the gene is associated with the disorder CDG2I, the patient showed atypical features such as global developmental delay, microcephaly, cleft palate, ambiguous genitalia and agenesis of corpus callosum.   

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