Congenital Disorders of Glycosylations (CDGs) are a group of metabolic disorders characterized by defective N-terminal glycosylation of proteins, which leads to the build-up of intermediate chemical compounds in the body, causing a variety of complications. Of all the CGDs, CGD1a is the most common, with about 70% of all patients affected with CGDs belonging to this type. CDG1a presents as a severe neonatal abnormality, and is typified by liver insufficiency, cerebellar hypoplasia, ataxia, peripheral neuropathy, psychomotor retardation, skeletal deformities, axial hypotonia with hyporeflexia, abnormal eye movements, visual and/or hearing impairment, and a characteristic deposition of adipose tissue in the form of fat pads. Retinitis pigmentosa, hypogonadism, nipple retraction, and mild facial dysmorphism may also be noticed in affected children. Prognosis for the condition is not very good, with about 20% of affected infants succumbing to liver, cardiac, or renal complications before the age of five years.
CDG1a has been found to be linked to mutations in the PMM2 gene, which encodes the phosphomannomutase-2 enzyme. This enzyme is involved in the synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions. CDG1a is inherited in an autosomal recessive manner.
In a study to estimate the prevalence of commonly diagnosed autosomal recessive diseases in Oman from a hospital-based register in 1993 to 2002, Rajab et al. (2005) found that Carbohydrate Deficient Glycoprotein Syndrome was diagnosed in eight patients, with an observed incidence of 1 in 50,000 births.