ALG9

ALG9 alpha-1,2-mannosyltransferase

3 disorders 2 untyped 1 causative 11q23.1 gene with protein product

HGNC:15672 Monarch NCBI Gene 79796 ENSG00000086848 UniProt Q9H6U8 OMIM 606941

Previous symbols: DIBD1.

Normal function · from ai-gene-review (Q9H6U8, commit 79fe13b38970) · AI-generated, not KB evidence

ALG9 is a glycosyltransferase 22 (GT22) family enzyme in the endoplasmic reticulum membrane. Its luminal catalytic site uses dolichyl-phosphate-mannose to build the oligomannose core of the lipid-linked precursor for protein N-linked glycosylation. ALG9 adds an alpha-1,2-linked seventh mannose to Man(6)GlcNAc(2)-PP-dolichol (EC 2.4.1.259) and, after ALG12 adds the eighth mannose, adds an alpha-1,2-linked ninth mannose to Man(8)GlcNAc(2)-PP-dolichol (EC 2.4.1.261). Human isoform 1 has 11 transmembrane helices. Reduced ALG9 activity causes accumulation of the Man6 and Man8 lipid-linked intermediates and deficient protein glycosylation. Biallelic pathogenic variants cause ALG9 congenital disorder of glycosylation (ALG9-CDG), including severe Gillessen-Kaesbach-Nishimura skeletal dysplasia with renal and other visceral malformations.

ALG9 transfers the seventh mannose from dolichyl-phosphate-mannose to the Man6 lipid-linked N-glycan precursor at the luminal face of the ER membrane. This completes the B branch before the intervening ALG12 addition.

molecular function: dol-P-Man:Man(6)GlcNAc(2)-PP-Dol alpha-1,2-mannosyltransferase activity · directly involved in: dolichol-linked oligosaccharide biosynthetic process · locations: lumenal side of endoplasmic reticulum membrane

ALG9 transfers the ninth mannose from dolichyl-phosphate-mannose to the Man8 lipid-linked N-glycan precursor at the luminal face of the ER membrane. This completes the C branch after ALG12 adds the eighth mannose.

molecular function: dol-P-Man:Man(8)GlcNAc(2)-PP-Dol alpha-1,2-mannosyltransferase activity · directly involved in: dolichol-linked oligosaccharide biosynthetic process · locations: lumenal side of endoplasmic reticulum membrane

In the knowledge base · computed from kb/ at build time

Disorders

Relationship is the entry's genetic[].relationship_type. untyped means the entry has a genetic record for the gene but does not type it; its free-text association is shown instead.

Disorder	Relationship	Where the gene appears
Polycystic Kidney Disease	causative	mechanism: Defective Polycystin-1 Maturation in the Endoplasmic Reticulum subtype: Autosomal Dominant PKD (ADPKD) scoped to subtype: Autosomal Dominant PKD (ADPKD)
ALG9-congenital disorder of glycosylation	untyped Biallelic loss-of-function variants	mechanism: ALG9 alpha-1,2-mannosyltransferase deficiency diagnosis: ALG9 molecular genetic testing
Autosomal Dominant Polycystic Kidney Disease	untyped CAUSATIVE	mechanism: Reduced ALG9 mannosyltransferase activity subtype: ALG9-associated ADPKD

ClinGen gene–disease validity · snapshot 2026-10-03 · matched to entries by MONDO

An entry matches when ClinGen's MONDO disease is the entry's own disease term, a subtype term, or an exact-match mapping. An amber status marks an entry ClinGen supports the gene for (Definitive, Strong or Moderate) whose own record does not type it. A Limited, Disputed or Refuted tier on such an entry is not a gap.

ClinGen disease	MOI	Classification	dismech entry
ALG9-associated autosomal dominant polycystic kidney disease MONDO:0700000	AD	Definitive 2023-09-11	Autosomal Dominant Polycystic Kidney Disease untyped

Mechanism modules · computed from kb/

congenital_disorder_of_glycosylation via ALG9-congenital disorder of glycosylation

Identity from HGNC (snapshot 2026-10-01). Page layers are described in the gene pages documentation.