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COG5-congenital disorder of glycosylation
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

COG5-congenital disorder of glycosylation

COG5-congenital disorder of glycosylation (COG5-CDG) is an extremely rare inherited condition that disrupts protein modification, leading to developmental delays, intellectual disability, and distinct physical features.

Overview

COG5-congenital disorder of glycosylation (COG5-CDG, formerly known as congenital disorder of glycosylation type IIi) is an inherited condition that causes neurological problems and other physical abnormalities. The pattern and severity of the signs and symptoms vary among affected individuals.

Symptoms

Signs and symptoms of COG5-CDG typically develop during infancy. Affected individuals often experience weak muscle tone (hypotonia) and delayed development. Other neurological and physical features include:

  • Moderate to severe intellectual disability
  • Poor coordination and difficulty walking
  • Inability to speak in some cases
  • Short stature
  • An unusually small head size
  • Distinctive facial features, including low-set and backward-rotated ears, a short neck with a low hairline in the back, and a prominent nose

Less common features of the disorder include:

  • Hearing loss caused by changes in the inner ear (sensorineural hearing loss)
  • Vision impairment
  • Damage to the nerves that control bladder function (neurogenic bladder)
  • Liver disease
  • Joint deformities (contractures)

Frequency

COG5-CDG is an extremely rare disorder. Fewer than 10 cases have been described in the medical literature.

Causes

COG5-CDG is caused by mutations in the COG5 gene. This gene provides instructions for producing one component of a group of proteins known as the conserved oligomeric Golgi (COG) complex. This complex operates within the Golgi apparatus, a cellular structure where newly produced proteins are modified.

One of the primary processes in the Golgi apparatus is glycosylation, which attaches sugar molecules (oligosaccharides) to proteins and fats, allowing them to perform a wider variety of functions. The COG complex helps transport the proteins, including those responsible for glycosylation, within the Golgi apparatus.

Mutations in the COG5 gene reduce or completely eliminate the COG5 protein, disrupting this transport process. This disruption leads to abnormal protein glycosylation, which affects multiple body systems and produces the signs and symptoms of the condition. The severity of COG5-CDG is directly related to the amount of functional COG5 protein that remains in the cells.

Inheritance

This condition is inherited in an autosomal recessive pattern, meaning both copies of the gene in each cell must have mutations for the disorder to develop. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • Carbohydrate deficient glycoprotein syndrome type IIi
  • CDG IIi
  • CDG2I
  • CDGIIi
  • COG5-CDG
  • Congenital disorder of glycosylation type IIi

Frequently Asked Questions

Management for COG5-CDG focuses on supportive therapies to address specific symptoms. This often includes physical therapy to improve muscle tone and coordination, occupational therapy for daily living skills, and speech therapy for communication difficulties. Early intervention programs are crucial to maximize developmental potential, and educational support will be tailored to the individual's intellectual disability.
COG5-CDG is inherited in an autosomal recessive pattern. This means an individual must inherit two copies of the mutated COG5 gene (one from each parent) to develop the condition. Parents of an affected child are typically carriers, meaning they each have one copy of the mutated gene but do not show symptoms. For each subsequent pregnancy, there is a 25% chance the child will be affected, a 50% chance they will be a carrier, and a 25% chance they will not inherit the mutation at all. Genetic counseling is highly recommended for families.
Children with COG5-CDG require comprehensive, multidisciplinary care. Regular monitoring should include neurological evaluations, developmental assessments, and screenings for less common features such as hearing loss (audiology), vision impairment (ophthalmology), and liver function (hepatology). Urological assessments may also be necessary if neurogenic bladder is suspected. The exact monitoring schedule will be determined by the child's specific symptoms and needs.
Diagnosis of COG5-CDG typically begins with a clinical evaluation based on the characteristic developmental delays, neurological problems, and distinctive physical features observed in infancy. Due to its rarity and overlapping symptoms with other conditions, genetic testing to identify mutations in the COG5 gene is essential to confirm the diagnosis. Specialized laboratory tests that analyze glycosylation patterns may also be used.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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