PMM2-CDG, the most common of a group of disorders of abnormal glycosylation of N-linked oligosaccharides, is divided into three clinical stages: infantile multisystem, late-infantile and childhood ataxia–intellectual disability, and adult stable disability. The clinical manifestations and course are highly variable, ranging from infants who die in the first year of life to mildly affected adults. Clinical findings tend to be similar in sibs. In the infantile multisystem presentation, infants show axial hypotonia, hyporeflexia, esotropia, and developmental delay. Feeding problems, vomiting, faltering growth, and developmental delay are frequently seen. Subcutaneous fat may be excessive over the buttocks and suprapubic region. Two distinct clinical courses are observed: (1) a nonfatal neurologic course with faltering growth, strabismus, developmental delay, cerebellar hypoplasia, and hepatopathy in infancy followed by neuropathy and retinitis pigmentosa in the first or second decade; and (2) a more severe neurologic-multivisceral course with approximately 20% mortality in the first year of life. The late-infantile and childhood ataxia–intellectual disability stage, which begins between ages three and ten years, is characterized by hypotonia, ataxia, severely delayed language and motor development, inability to walk, and IQ of 40 to 70; other findings include seizures, stroke-like episodes or transient unilateral loss of function, coagulopathy, retinitis pigmentosa, joint contractures, and skeletal deformities. In the adult stable disability stage, intellectual ability is stable; peripheral neuropathy is variable, progressive retinitis pigmentosa and myopia are seen, thoracic and spinal deformities with osteoporosis worsen, and premature aging is observed; females may lack secondary sexual development and males may exhibit decreased testicular volume. Hypogonadotropic hypogonadism and coagulopathy may occur. The risk for deep venous thrombosis is increased.

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. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). CDG1D is a type I CDG that generally presents with severe neurologic involvement associated with dysmorphism and visual impairment. Liver involvement is sometimes present (summary by Marques-da-Silva et al., 2017). For a discussion of the classification of CDGs, see CDG1A (212065).

DOLK-congenital disorder of glycosylation (DOLK-CDG, formerly known as congenital disorder of glycosylation type Im) is an inherited condition that often affects the heart but can also involve other body systems. The pattern and severity of this disorder's signs and symptoms vary among affected individuals.\n\nIndividuals with DOLK-CDG typically develop signs and symptoms of the condition during infancy or early childhood. Nearly all individuals with DOLK-CDG develop a weakened and enlarged heart (dilated cardiomyopathy). Other frequent signs and symptoms include recurrent seizures; developmental delay; poor muscle tone (hypotonia); and dry, scaly skin (ichthyosis). Less commonly, affected individuals can have distinctive facial features, kidney disease, hormonal abnormalities, or eye problems.\n\nIndividuals with DOLK-CDG typically do not survive into adulthood, often because of complications related to dilated cardiomyopathy, and some do not survive past infancy.

Congenital disorders of glycosylation (CDGs) are metabolic deficiencies in glycoprotein biosynthesis that usually cause severe mental and psychomotor retardation. Different forms of CDGs can be recognized by altered isoelectric focusing (IEF) patterns of serum transferrin. For a general discussion of CDGs, see CDG Ia (212065) and CDG Ib (602579).

Congenital disorder of glycosylation type Ii (CDG1I) is a rare autosomal recessive disorder characterized by neurologic involvement, including a convulsive syndrome of unknown origin, axial hypotonia, and mental and motor regression (summary by Papazoglu et al., 2021). For a general discussion of CDGs, see CDG1A (212065).

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. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). For a discussion of the classification of CDGs, see CDG1A (212065). CDG Ib is clinically distinct from most other CDGs by the lack of significant central nervous system involvement. The predominant symptoms are chronic diarrhea with failure to thrive and protein-losing enteropathy with coagulopathy. Some patients develop hepatic fibrosis. CDG Ib is also different from other CDGs in that it can be treated effectively with oral mannose supplementation, but can be fatal if untreated (Marquardt and Denecke, 2003). Thus, CDG Ib should be considered in the differential diagnosis of patients with unexplained hypoglycemia, chronic diarrhea, liver disease, or coagulopathy in order to allow early diagnosis and effective therapy (Vuillaumier-Barrot et al., 2002) Freeze and Aebi (1999) reviewed CDG Ib and CDG Ic (603147). Marques-da-Silva et al. (2017) systematically reviewed the literature concerning liver involvement in CDG.

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. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). For a discussion of the classification of CDGs, see CDG1A (212065).

Limb-girdle muscular dystrophy-dystroglycanopathy type C15 (MDDGC15) is an autosomal recessive disorder characterized by progressive proximal muscle weakness, manifest initially as unsteady gait, but later including more distal muscles, and dilated cardiomyopathy. The age at onset varies widely from the first decade to adulthood; those with earlier onset may have delayed motor development. Laboratory studies show increased serum creatine kinase and muscle biopsy shows dystrophic features with decreased alpha-dystroglycan (DAG1; 128239). Biochemical studies often show evidence of abnormal N-glycosylation of serum proteins, consistent with a congenital disorder of glycosylation (CDG) (summary by Svahn et al., 2019). For a discussion of genetic heterogeneity of muscular dystrophy- dystroglycanopathy type C, see MDDGC1 (609308). For a discussion of the classification of CDGs, see CDG1A (212065).

Congenital disorders of glycosylation, previously called carbohydrate-deficient glycoprotein syndromes (CDGSs), are caused by defects in mannose addition during N-linked oligosaccharide assembly. CDGs can be divided into 2 types, depending on whether they impair lipid-linked oligosaccharide (LLO) assembly and transfer (CDG I), or affect trimming of the protein-bound oligosaccharide or the addition of sugars to it (CDG II) (Orlean, 2000). CDG Ic is characterized by psychomotor retardation with delayed walking and speech, hypotonia, seizures, and sometimes protein-losing enteropathy. It is the second largest subtype of CDG (summary by Sun et al., 2005). For a discussion of the classification of CDGs, see CDG1A (212065). Freeze and Aebi (1999) reviewed CDG Ib (602579) and CDG Ic.

Congenital disorders of glycosylation (CDG), previously called carbohydrate-deficient glycoprotein syndromes (CDGSs), are a group of hereditary multisystem disorders first recognized by Jaeken et al. (1980). The characteristic biochemical abnormality of CDGs is the hypoglycosylation of glycoproteins, which is routinely determined by isoelectric focusing (IEF) of serum transferrin. Type I CDG comprises those disorders in which there is a defect in the assembly of lipid-linked oligosaccharides or their transfer onto nascent glycoproteins, whereas type II CDG comprises defects of trimming, elongation, and processing of protein-bound glycans. CDG1G is a multisystem disorder characterized by impaired psychomotor development, dysmorphic features, failure to thrive, male genital hypoplasia, coagulation abnormalities, and immune deficiency. More variable features include skeletal dysplasia, cardiac anomalies, ocular abnormalities, and sensorineural hearing loss. Some patients die in the early neonatal or infantile period, whereas others are mildly affected and live to adulthood (summary by Tahata et al., 2019). For a general discussion of CDGs, see CDG1A (212065).

CDGs, previously called carbohydrate-deficient glycoprotein syndromes, grew from hereditary multisystem disorders first recognized by Jaeken et al. (1980). The characteristic biochemical abnormality of CDGs is the hypoglycosylation of glycoproteins, which is routinely determined by isoelectric focusing of serum transferrin. Type I CDG comprises those disorders in which there is a defect in the assembly of lipid-linked oligosaccharides or their transfer onto nascent glycoproteins, whereas type II CDG comprises defects of trimming, elongation, and processing of protein-bound glycans. For a general discussion of CDGs, see CDG1A (212065). CDG1H is a severe form of CDG. The majority of patients have brain involvement, liver pathology, gastrointestinal symptoms, dysmorphism (including brachydactyly), eye involvement (especially cataract), and skin symptoms. Most patients die within the first year of life (summary by Marques-da-Silva et al., 2017).

Like all CDGs, which are caused by a shortage of precursor monosaccharide phosphate or deficiencies in the glycosyltransferases required for lipid-linked oligosaccharide precursor (LLO) synthesis, CDG Ij is caused by a defect in the formation of DPAGT1, the first dolichyl-linked intermediate of the protein N-glycosylation pathway. For a general discussion of CDGs, see CDG1A (212065).

Congenital disorders of glycosylation (CDGs) comprise a group of multisystem diseases with mostly severe psychomotor and mental retardation. Type I CDG comprises those disorders in which there are defects that affect biosynthesis of dolichol-linked oligosaccharides in the cytosol or the endoplasmic reticulum (ER), as well as defects involving the transfer of oligosaccharides onto nascent glycoproteins. Type II CDG comprises all defects of further trimming and elongation of N-linked oligosaccharides in the ER and Golgi (Schwarz et al., 2004). CDG1K is a type I CDG characterized by predominant neurologic involvement. Survival ranges from the second day of life to adulthood. The liver is affected in a minority of patients and shows hepatomegaly, edema, ascites, cholestatic jaundice, portal hypertension, and Budd-Chiari syndrome (summary by Marques-da-Silva et al., 2017). For a general discussion of CDGs, see CDG1A (212065).

Congenital disorders of glycosylation (CDGs) that represent defects of dolichol-linked oligosaccharide assembly are classified as CDG type I. For a general description and a discussion of the classification of CDGs, see CDG1A (212065).

A form of congenital disorders of N-linked glycosylation with characteristics of facial dysmorphism (microcephaly, high forehead, low posterior hairline, strabismus), hypotonia, failure to thrive, intractable seizures, developmental delay, persistent vomiting and gastric bleeding. Additional features that may be observed include fat pads anomalies, inverted nipples, and body temperature oscillation. The disease is caused by mutations in the gene ALG11 (13q14.3).

Congenital disorder of glycosylation type Ir (CDG1R) is an autosomal recessive disorder characterized by developmental delay, failure to thrive, feeding difficulties, hypotonia, and strabismus. Transferrin analysis demonstrates underglycosylation (summary by Pi et al., 2022). For a discussion of the classification of CDGs, see CDG1A (212065).

A form of congenital disorders of N-linked glycosylation with characteristics of neurologic abnormalities (global developmental delay in language, social skills and fine and gross motor development, intellectual disability, hypotonia, microcephaly, seizures/epilepsy), facial dysmorphism (deep set eyes, large ears, hypoplastic vermillion of upper lip, large mouth with widely spaced teeth), feeding problems often due to chewing difficulties and aversion to food with certain textures, failure to thrive, gastrointestinal abnormalities (reflux or vomiting) and strabismus. The disease is caused by mutations in the gene SSR4 (Xq28).

SRD5A3-congenital disorder of glycosylation (SRD5A3-CDG, formerly known as congenital disorder of glycosylation type Iq) is an inherited condition that causes neurological and vision problems and other signs and symptoms. The pattern and severity of this condition's features vary widely among affected individuals.\n\nIndividuals with SRD5A3-CDG typically develop signs and symptoms of the condition during infancy or early childhood. Most individuals with SRD5A3-CDG have intellectual disability, vision problems, unusual facial features,low muscle tone (hypotonia), and problems with coordination and balance (ataxia). \n\nVision problems in SRD5A3-CDG often include involuntary side-side movements of the eyes (nystagmus), a gap or hole in one of the structures of the eye (coloboma), underdevelopment of the nerves that carry signals between the eyes and the brain(optic nerve hypoplasia), or vision loss early in life (early-onset severe retinal dystrophy). Over time, affected individuals may develop clouding of the lenses of the eyes (cataracts) or increased pressure in the eyes (glaucoma).\n\nOther features of SRD5A3-CDG can include skin rash, unusually small red blood cells (microcytic anemia),and liver problems.

Developmental and epileptic encephalopathy-36 (DEE36) is an X-linked neurodevelopmental disorder characterized by the onset of seizures at a mean age of 6.5 months. Most patients present with infantile spasms associated with hypsarrhythmia on EEG, consistent with a clinical diagnosis of West syndrome. The seizures tend to be refractory to treatment, although some patients may respond to benzodiazepines or a ketogenic diet. Affected individuals have severely delayed psychomotor development with poor motor function, severe intellectual disability, poor or absent speech, and limited eye contact. More variable features include feeding difficulties sometimes requiring tube feeding, ocular defects including cortical visual impairment, dysmorphic facial features, and scoliosis or osteopenia. The vast majority of patients reported have been females, although rare affected males with a similar phenotype have been described. Most patients show normal N-glycosylation on transferrin isoelectric focusing, but some show abnormal N-glycosylation consistent with CDG type I (summary by Ng et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of the classification of CDGs, see CDG1A (212065).