Congenital disorder of glycosylation type 1X/IIX

Overview

General Introduction about Congenital disorder of glycosylation:

Congenital disorder of glycosylation (carbohydrate-deficient glycoprotein syndrome) is one of several rare inborn errors of metabolism in which glycosylation of a variety of tissue proteins and/or lipids 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.

Congenital disorders of glycosylation (CDG) is an umbrella term for a rapidly expanding group of rare genetic, metabolic disorders due to defects in complex chemical process known as glycosylation. Glycosylation is the process by which sugar 'trees' (glycans) are created, altered and chemically attached to certain proteins or fats (lipids). When these sugar molecules are attached to proteins, they form glycoproteins; when they are attached to lipids, they form glycolipids. Glycoproteins and glycolipids have numerous important functions in all tissues and organs.

Glycosylation involves many different genes, encoding many different proteins such as enzymes. A deficiency or lack of one of these enzymes can lead to a variety of symptoms potentially affecting multiple organ systems. CDG can affect any part of the body, and there is nearly always an important neurological component. CDG can be associated with a broad variety of symptoms and can vary in severity from mild cases to severe, disabling or life-threatening cases. CDG are usually apparent from infancy. Individual CDG are caused by a mutation to a specific gene. Most CDG are inherited as autosomal recessive conditions.

CDG was first reported in the medical literature in 1980 by Dr. Jaak Jaeken and colleagues. More than 80 different forms of CDG have been identified in the ensuing years. Several different names have been used to describe these disorders including carbohydrate-deficient glycoprotein syndromes. Recently, Jaeken and colleagues have proposed a classification system that names each subtype by the official abbreviation of its defective gene followed by a dash and CDG. For example, congenital disorder of glycosylation type 1a is now known as PMM2-CDG. PMM2 is the defective gene that causes this subtype of CDG.

CDGs are classified as 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. The most commonly used screening method for CDG, analysis of transferrin glycosylation status by isoelectric focusing, ESI-MS, or other techniques, distinguish between these subtypes, which are called Type I and Type II patterns. Currently, twenty-two CDG Type-I and fourteen Type-II subtypes of CDG have been described.

Congenital disorder of glycosylation type 1/IIX:

An increasing number of individuals have been reported with unidentified defects of glycosylation. Some of these individuals have signs and symptoms that are similar to other subtypes of CDG, while other individuals have signs and symptoms that have not been reported in CDG before. Such unidentified cases are collectively referred to as CDG-x.

Type 1X also involves thrombocytopenia with normal levels of phosphomannomutase and phosphomannose isomerase. This form of the condition is severe and results in death during infancy.

As long as the defect is not identified, disorders of N-glycosylation are subdivided into defects of oligosaccharide assembly and transfer (CDG-Ix) and defects in oligosaccharide trimming and processing that occur after they are bound to proteins (CDG-IIx).

Symptoms

  • Severe thrombocytopenia
  • Breathing problems
  • Normal phosphomannose isomerase activity
  • Normal phosphomannomutase activity
  • Infant death
  • Failure to thrive
  • Unusual facial appearance
  • Heart problems
  • Enlarged liver
  • Feeding problems
  • Diarrhea
  • Vomiting
  • Abnormal deposits of fat on body
  • Seizures
  • Reduced muscle tone
  • Abnormality of coagulation
  • Abnormality of immune system physiology
  • Abnormality of retinal pigmentation
  • Aplasia/Hypoplasia of the cerebellum
  • Aplasia/Hypoplasia of the nipples
  • Cerebral cortical atrophy
  • Cognitive impairment
  • Elevated hepatic transaminases
  • Strabismus

Treatment

No treatment is available for most of these disorders.