A large group of disorders arising during development that cause abnormality of the human body. Most are due to genetic factors such as inherited or spontaneous mutations, whereas others are caused by environmental influences during pregnancy such as exposure to harmful chemicals. The most severe and lethal disorders arise during the first 28 days of development and include gross brain anomalies and heart defects. The mildest malformations occur in the late stages of development and are often the result of dominant inheritance, whereas complex congenital syndromes are often the result of recessive inheritance. Seealso birth defect; Down syndrome.

Learn more about congenital disorder with a free trial on Britannica.com.

A congenital disorder of glycosylation (previously called carbohydrate-deficient glycoprotein syndrome) is one of several rare inborn errors of metabolism in which N-glycosylation of a variety of tissue proteins is deficient or defective. Congenital disorders of glycosylation are sometimes known as CDG syndromes. They often cause serious, sometimes fatal, malfunction of several different organ systems (especially the nervous system, muscles, and intestines) in affected infants.

History

They were discovered in the late 1990s. Delineation of types and manifestations has been expanding rapidly, with several new forms described each year since then.

Classification

CDG are classified as CDG types I and II (CDG-I and CDG-II), depending on the nature and location of the biochemical defect in the metabolic pathway relative to the action of oligosaccharyltransferase.

• Type I disorders involve disrupted synthesis of the lipid-linked oligosaccharide precursor.
• Type II disorders involve malfunctioning trimming/processing of the protein-bound oligosaccharide chain.

Currently, twelve CDG type-I variants have been identified (CDG-Ia to -Il) and six variants of CDG Type-II have been described (CDG-IIa to -IIe).

Presentation

The specific problems produced differ according to the particular abnormal synthesis involved. Common manifestations include ataxia; seizures; retinopathy; liver fibrosis; coagulopathies; failure to thrive; dysmorphic features (e.g., inverted nipples and subcutaneous fat pads; and strabismus.

Ocular abnormalities of CDG-Ia include: myopia, infantile esotropia, delayed visual maturation, low vision, optic pallor, and reduced rod function on electroretinography.

Three subtypes of CDG I (a,b,d) can cause congenital hyperinsulinism with hyperinsulinemic hypoglycemia in infancy.

Treatment

No treatment is available for most of these disorders. Mannose supplementation has produced some benefits in a couple of the Type I subtypes. Several synthetic glycoconjugate compounds have been synthesized and are being tested for therapeutic efficacy.

See also

• Inborn error of metabolism

References

External links

• The CDG Family Network