From OMIM
Congenital disorders of glycosylation (CDGs) are a genetically heterogeneous group of autosomal recessive disorders caused by enzymatic defects in the synthesis and processing of asparagine (N)-linked glycans or oligosaccharides on glycoproteins. These glycoconjugates play critical roles in metabolism, cell recognition and adhesion, cell migration, protease resistance, host defense, and antigenicity, among others. CDGs are divided into 2 main groups: type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein, whereas type II CDGs (see, e.g., CDG2A, 212066) refer to defects in the trimming and processing of the protein-bound glycans either late in the endoplasmic reticulum or the Golgi compartments. CDG1A is the most common form of CDG and was the first to be characterized at the molecular level (reviews by Marquardt and Denecke, 2003; Grunewald et al., 2002). Matthijs et al. (1997) noted that Jaeken syndrome (CDG1A) is a genetic multisystem disorder characterized by defective glycosylation of glycoconjugates. It usually presents as a severe disorder in the neonatal period. There is a severe encephalopathy with axial hypotonia, abnormal eye movement, and pronounced psychomotor retardation, as well as peripheral neuropathy, cerebellar hypoplasia, and retinitis pigmentosa. Patients show a peculiar distribution of subcutaneous fat, nipple retraction, and hypogonadism. There is a 20% lethality in the first year of life due to severe infections, liver insufficiency, or cardiomyopathy. Marques-da-Silva et al. (2017) noted that CDG1A is the most prevalent form of CDG, with more than 700 patients reported worldwide. Genetic Heterogeneity of Congenital Disorder of Glycosylation Type I Multiple forms of CDG type I have been identified; see CDG1B (602579) through CDG1Y (300934) and CDG1AA (617082) through CDG1CC (see 301031). A congenital disorder of deglycosylation (CDDG; 615273), formerly designated CDG1V, is caused by mutation in the NGLY1 gene (610661). A disorder formerly designated CDG1Z has been classified as a form of developmental and epileptic encephalopathy (DEE50; 616457).  http://www.omim.org/entry/212065

From MedlinePlus Genetics
PMM2-congenital disorder of glycosylation (PMM2-CDG, also known as congenital disorder of glycosylation type Ia) is an inherited condition that affects many parts of the body. The type and severity of problems associated with PMM2-CDG vary widely among affected individuals, sometimes even among members of the same family.

Individuals with PMM2-CDG typically develop signs and symptoms of the condition during infancy. Affected infants may have weak muscle tone (hypotonia), retracted (inverted) nipples, an abnormal distribution of fat, eyes that do not look in the same direction (strabismus), developmental delay, and a failure to gain weight and grow at the expected rate (failure to thrive). Infants with PMM2-CDG also frequently have an underdeveloped cerebellum, which is the part of the brain that coordinates movement. Distinctive facial features are sometimes present in affected individuals, including a high forehead, a triangular face, large ears, and a thin upper lip. Children with PMM2-CDG may also have elevated liver function test results, seizures, fluid around the heart (pericardial effusion), and blood clotting disorders. About 20 percent of affected infants do not survive the first year of life due to multiple organ failure.

The most severe cases of PMM2-CDG are characterized by hydrops fetalis, a condition in which excess fluid builds up in the body before birth. Most babies with hydrops fetalis are stillborn or die soon after birth.

People with PMM2-CDG who survive infancy may have moderate intellectual disability, and some are unable to walk independently. Affected individuals may also experience stroke-like episodes that involve an extreme lack of energy (lethargy) and temporary paralysis. Recovery from these episodes usually occurs over a period of a few weeks to several months.

During adolescence or adulthood, individuals with PMM2-CDG have reduced sensation and weakness in their arms and legs (peripheral neuropathy), an abnormal curvature of the spine (kyphoscoliosis), impaired muscle coordination (ataxia), and joint deformities (contractures). Some affected individuals have an eye disorder called retinitis pigmentosa that causes vision loss. Females with PMM2-CDG have hypergonadotropic hypogonadism, which affects the production of hormones that direct sexual development. As a result, females with PMM2-CDG do not go through puberty. Affected males experience normal puberty but often have small testes.  https://medlineplus.gov/genetics/condition/pmm2-congenital-disorder-of-glycosylation