This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "congenital_disorder_of_glycosylation#Protein Hypoglycosylation"). The single best key conformance target is the central "Protein Hypoglycosylation" node — the one event every CDG shares regardless of arm, matching the machine-checkable GO:0006487 / GO:0006491 criterion already used by the Congenital_Disorders_of_Glycosylation grouping. A type I conformer routes through the "ER Lipid-Linked Oligosaccharide Assembly Defect" trigger; a type II conformer routes through the "Golgi N-Glycan Processing and Trafficking Defect" trigger; both then conform to the shared "Protein Hypoglycosylation" hub. Conforming nodes should substitute the disorder-specific lesion (the deficient ER glycosyltransferase or dolichol-donor-utilization factor for type I; the deficient Golgi processing enzyme or COG-trafficking subunit for type II). The specificity is carried by the mechanism (hypoglycosylation), not by the diffuse terminal phenotype; disorder-private downstream biology (alpha-dystroglycan O-mannosylation in MPDU1, hyposialylation in the COG disorders) belongs on the individual disorder entries. Modules bind GO and CL terms only and do not use CHEBI or gene bindings. This broad N-glycan-centered convergence module is distinct from tsr_o_glycosylation_quality_control, which models folded-TSR O-fucose/glucose quality control for a selective client set rather than generalized glycoprotein hypoglycosylation.
ER Lipid-Linked Oligosaccharide Assembly Defect
trigger
In the type I CDG, one of the enzymes (or dolichol-donor-utilization factors) that build the lipid-linked oligosaccharide precursor on the cytosolic and luminal faces of the endoplasmic reticulum is deficient. The dolichol-linked oligosaccharide is assembled incompletely, so a truncated precursor accumulates and truncated/incomplete oligosaccharides are transferred to nascent protein instead of the full mature glycan.
Downstream
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Protein Hypoglycosylation
Show evidence (1 reference)
"Using this approach, we have found, in a patient with CDG, a deficiency of the ALG9 alpha 1,2 mannosyltransferase enzyme, which causes an accumulation of lipid-linked-GlcNAc(2)Man(6) and -GlcNAc(2)Man(8) structures, which was paralleled by the transfer of incomplete oligosaccharides precursors..."
Worked type I example establishing the conserved ER trigger — an LLO assembly enzyme deficiency causes truncated-precursor accumulation and transfer of incomplete oligosaccharides to protein. Evidence source is IN_VITRO because this is a cultured-fibroblast biochemical study.
Golgi N-Glycan Processing and Trafficking Defect
trigger
In the type II CDG, the oligosaccharide precursor is transferred to protein normally, but its subsequent maturation in the Golgi is defective — either because a Golgi processing enzyme is deficient (e.g. MGAT2, which encodes N-acetylglucosaminyltransferase II, the branching enzyme that converts oligomannose to complex N-glycans) or because trafficking of the Golgi glycosylation machinery is disrupted (e.g. the conserved oligomeric Golgi (COG) complex disorders, which mislocalize Golgi glycosyltransferases and disrupt multiple glycosylation pathways).
Downstream
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Protein Hypoglycosylation
Show evidence (2 references)
"Human MGAT2 encodes N-acetylglucosaminyltransferase II, which is a critical enzyme in the processing of oligomannose to complex N-glycans."
Establishes the Golgi-processing sub-arm of the type II trigger — MGAT2 is the branching enzyme that matures oligomannose to complex N-glycans.
"The mutation impairs integrity of the COG complex and alters Golgi trafficking, resulting in disruption of multiple glycosylation pathways."
Establishes the Golgi-trafficking sub-arm of the type II trigger — COG complex disruption alters Golgi trafficking and disrupts multiple glycosylation pathways. Evidence source is IN_VITRO because this is a cell-based study.
Protein Hypoglycosylation
central effector
Both arms converge here: many secreted and membrane client glycoproteins carry absent, truncated, or otherwise abnormal glycans. In the type I disorders this is detected as the classic cathodal shift of serum transferrin (CDG type 1 isoelectric-focusing pattern); in the COG and other type II disorders it manifests as combined deficient N- and O-glycosylation. Because glycosylation modifies a very large fraction of the proteome, hypoglycosylation degrades the folding, stability, trafficking, and function of many unrelated proteins simultaneously — the shared central lesion of the disease family.
Downstream
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Multisystem Glycoprotein Dysfunction
Show evidence (2 references)
"Hypoglycosylation was confirmed by the typical CDG type 1 pattern of serum transferrin analyzed by isoelectric focusing."
Establishes the shared central lesion for the type I arm — protein hypoglycosylation demonstrated by the classic CDG type 1 transferrin pattern.
"COG defects are a novel group of CDG-II with deficient N- as well as O-glycosylation."
Establishes the shared central lesion for the type II/COG arm — combined deficient N- and O-glycosylation. Evidence source is OTHER because this is a review synthesizing the COG-CDG group.
Multisystem Glycoprotein Dysfunction
consequence
Because so many glycoproteins are simultaneously affected, the downstream disease is characteristically multisystem: developmental delay/intellectual disability, hypotonia, and other neurologic features; hepatic dysfunction; coagulation abnormalities; immune dysfunction; dysmorphism; and, in some subtypes, skeletal or renal involvement. The precise organ pattern varies by subtype and by which client glycoproteins are most rate-limiting, but the multisystem outflow is the shared consequence of proteome-wide hypoglycosylation.
Show evidence (1 reference)
"All three suffered from intellectual disability, muscular hypotonia, microcephaly and renal cysts, but none had skeletal dysplasia."
Illustrates the conserved multisystem outflow (neurologic, muscular, growth, renal) of a worked CDG conformer downstream of hypoglycosylation.