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A form of congenital disorders of N-linked glycosylation characterized by progressive microcephaly, hypotonia, developmental delay, drug-resistant infantile epilepsy, and hepatomegaly. Additional features that may be observed include failure to thrive, pericardial effusion, renal cysts, skeletal dysplasia, facial dysmorphism (frontal bossing, hypertelorism, depressed nasal bridge, low-seated ears, large mouth) and hydrops fetalis. The disease is caused by loss-of-function mutations in the gene ALG9 (11q23).
Data assembled from 6 of 12 sources · Last updated Sep 20, 2026, 4:38 PM UTC
Online Mendelian Inheritance in Man
European rare disease database
Genetic and Rare Diseases Info Center
Common questions about ALG9-congenital disorder of glycosylation
Features include always present findings: Delayed CNS myelination, Seizure, Low muscle tone (hypotonia), and Hypoalbuminemia and others; and very common findings: Microcephaly and Failure to thrive. 47 total HPO annotations.
Organ System | Phenotype Count | Example Features |
|---|---|---|
Brain and nerves | 9 | Poor speech, Seizure, Intellectual disability |
Muscles | 5 | Low muscle tone (hypotonia), Shrinkage of the cerebellum (cerebellar atrophy), Global brain atrophy |
Digestive system | 3 | Ascites, Enlarged liver (hepatomegaly), Enlarged spleen (splenomegaly) |
Bones and joints | 3 | Delayed skeletal maturation, Skeletal dysplasia, Excessive outward curvature of the upper spine (kyphosis) |
Pregnancy and birth | 3 | Hydrops fetalis, Fetal skin edema, Decreased fetal movement |
Head and neck | 2 | Microcephaly, Abnormal facial shape |
Heart and blood vessels | 2 | Pericardial effusion, Atrial septal defect |
Kidneys and urinary system | 1 | Polycystic kidney dysplasia |
Growth and development | 1 | Failure to thrive |
Blood and immune system | 1 | Enlarged spleen (splenomegaly) |
Skin | 1 | Fetal skin edema |
Lungs and breathing | 1 | Asthma |
Age of onset: before birth, at birth.
ALG9 encodes ALG9 alpha-1,2-mannosyltransferase (611 aa). Mannosyltransferase that operates in the biosynthetic pathway of dolichol-linked oligosaccharides, the glycan precursors employed in protein asparagine (N)-glycosylation. Highest expression in Nerve Tibial (12.8 TPM) and Cervix Ectocervix (12.7 TPM).
ALG9-congenital disorder of glycosylation is associated with mutations in the ALG9 gene on chromosome 11.
The ALG9 protein participates in Defective ALG9 causes CDG-1l, Defective ALG12 causes CDG-1g, and Defective ALG6 causes CDG-1c pathways.
ALG9 is classified as a druggable target (Enzyme category) with score 0.0.
Genetic testing for ALG9 is available. Testing is considered confirmatory for diagnosis.
Phenotype severity distribution: 19 always present features, 2 very common features, 2 common features.
Estimated prevalence: <1 in 1,000,000 (VERY_RARE).
No clinical trials have been registered for ALG9-congenital disorder of glycosylation.
2 publications have been identified in PubMed for ALG9-congenital disorder of glycosylation. Research spans Basic Science / Preclinical (100%).
Alexander JAN (2026). [PMID: 41807832](https://pubmed.ncbi.nlm.nih.gov/41807832/). *Nat Chem Biol*. [Basic Science / Preclinical]
Matheny-Rabun C (2024). [PMID: 39561044](https://pubmed.ncbi.nlm.nih.gov/39561044/). *Cell Rep*. [Basic Science / Preclinical]
AI-curated news mentioning ALG9-congenital disorder of glycosylation
Updated Jul 21, 2026
FDA approved Casgevy CRISPR gene therapy for children as young as 2 with sickle cell disease on July 1, 2026. Here's what families need to know about this milestone. Approximately 5,500 additional American children are now eligible for this established one-time therapy, according to Vertex Pharmaceuticals, Casgevy's developer. Casgevy also covers transfusion-dependent beta-thalassemia in this new age indication. Sickle cell disease is a lifelong inherited blood disorder that warps red blood cells into stiff, crescent shapes that can block blood flow, starving organs and tissues of oxygen. The world's first CRISPR-based gene therapy has been approved for children as young as two years old, opening the possibility of a single, potentially curative treatment to thousands of American children with sickle cell disease before years of organ damage can narrow what medicine can do for them. Families with children aged 2 and older who have sickle cell disease should speak with their pediatric hematologist about whether Casgevy is appropriate to consider at this stage of their child's disease. Ask specifically which authorized treatment centers perform Casgevy in your region. Treatment is available only at specialized sites, and geographic access remains limited. Contact your child's insurance plan or Medicaid office to ask about coverage. Medicaid coverage for gene therapies varies by state, and some states have developed outcomes-based payment models for high-cost therapies. "With today's decision, pediatric patients as young as 2 years of age can now access a critical additional treatment option to treat these debilitating, life-threatening diseases," said Karim Mikhail, acting director of the Office of Therapeutic Products at the FDA's Center for Biologics Evaluation and Research, according to the FDA press announcement. Casgevy is a non-viral, ex vivo CRISPR/Cas9 gene-edited cell therapy.
A new treatment for children aged 2 or older with sickle cell disease has been approved by the U.S. Food & Drug Administration. In a press release on Wednesday, the FDA announced it had approved Casgevy, the first gene therapy for children with sickle cell disease. (NewsNation) — A new treatment for children aged 2 or older with sickle cell disease has been approved by the Food & Drug Administration (FDA). In a Wednesday news release, the FDA announced it had approved Casgevy, the first gene therapy for children with the disease. “Casgevy is a gene therapy consisting of the patient’s own (autologous) hematopoietic (blood) stem cells, administered as a one-time single dose for intravenous infusion,” the release noted. “Pediatric patients as young as 2 years of age can now access a critical additional treatment option to treat these debilitating, life-threatening diseases,” Karim Mikhail, the acting director of the Center for Biologics Evaluation and Research, wrote. “These disorders carry a heavy burden for children and their families, affecting growth, development, and long-term health in profound ways,” Megha Kaushal, acting deputy director of the Office of Therapeutic Products in CBER, said in the release.