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ALG6-congenital disorder of glycosylation

(often shortened to ALG6-CDG)
Reviewed May 2014

What is ALG6-CDG?

ALG6-congenital disorder of glycosylation (ALG6-CDG, also known as congenital disorder of glycosylation type Ic) is an inherited condition that affects many parts of the body. The signs and symptoms of ALG6-CDG vary widely among people with the condition.

Individuals with ALG6-CDG typically develop signs and symptoms of the condition during infancy. They may have difficulty gaining weight and growing at the expected rate (failure to thrive). Affected infants often have weak muscle tone (hypotonia) and developmental delay.

People with ALG6-CDG may have seizures, problems with coordination and balance (ataxia), or stroke-like episodes that involve an extreme lack of energy (lethargy) and temporary paralysis. They may also develop blood clotting disorders. Some individuals with ALG6-CDG have eye abnormalities including eyes that do not look in the same direction (strabismus) and an eye disorder called retinitis pigmentosa, which causes vision loss. Females with ALG6-CDG have hypergonadotropic hypogonadism, which affects the production of hormones that direct sexual development. As a result, most females with ALG6-CDG do not go through puberty.

How common is ALG6-CDG?

The prevalence of ALG6-CDG is unknown, but it is thought to be the second most common type of congenital disorder of glycosylation. More than 30 cases of ALG6-CDG have been described in the scientific literature.

What genes are related to ALG6-CDG?

ALG6-CDG is caused by mutations in the ALG6 gene. This gene provides instructions for making an enzyme that is involved in a process called glycosylation. Glycosylation is the process by which sugar molecules (monosaccharides) and complex chains of sugar molecules (oligosaccharides) are added to proteins and fats. Glycosylation modifies proteins and fats so they can perform a wider variety of functions. The enzyme produced from the ALG6 gene transfers a simple sugar called glucose to the growing oligosaccharide. Once the correct number of sugar molecules are linked together, the oligosaccharide is attached to a protein or fat.

ALG6 gene mutations lead to the production of an abnormal enzyme with reduced or no activity. Without a properly functioning enzyme, glycosylation cannot proceed normally, and oligosaccharides are incomplete. As a result, glycosylation is reduced or absent. The wide variety of signs and symptoms in ALG6-CDG are likely due to impaired glycosylation of proteins and fats that are needed for normal function in many organs and tissues, including the brain, eyes, liver, and hormone-producing (endocrine) system.

Read more about the ALG6 gene.

How do people inherit ALG6-CDG?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. 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.

Where can I find information about diagnosis or management of ALG6-CDG?

These resources address the diagnosis or management of ALG6-CDG and may include treatment providers.

You might also find information on the diagnosis or management of ALG6-CDG in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I find additional information about ALG6-CDG?

You may find the following resources about ALG6-CDG helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for ALG6-CDG?

  • carbohydrate-deficient glycoprotein syndrome type Ic
  • carbohydrate-deficient glycoprotein syndrome type V
  • CDG1C
  • CDGIc
  • CDG syndrome type Ic
  • congenital disorder of glycosylation type Ic
  • glucosyltransferase 1 deficiency

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about ALG6-CDG?

Where can I find general information about genetic conditions?

What glossary definitions help with understanding ALG6-CDG?

References (6 links)


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

Reviewed: May 2014
Published: February 1, 2016