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ALG12-congenital disorder of glycosylation

ALG12-congenital disorder of glycosylation



Overview

ALG12-congential disorder of glycosylation (ALG12-CDG) is a rare, inherited multi-system condition caused by mutations in the ALG12 Gene, leading to intellectual disability, weak muscle tone, and immune issues

Symptoms

Growth and Neurological Signs

Failure to thrive: Feeding difficulties and trouble gaining weight.

Hypotonia: Weak or low muscle tone.

Developmental delay: Delayed motor skills and moderate-to-severe intellectual disability.

Seizures: Developing in some affected individuals.Microcephaly: Progressive small head size.

Physical and Facial Features

Facial dysmorphism: Prominent nasal bridge or forehead, epicanthal eye folds, and abnormally shaped or large ears.

Skeletal abnormalities: Poor bone development and abnormal bone ossification.

Genital abnormalities: Micropenis and undescended testes (cryptorchidism) in males.

Immune and Other Complications

Low antibodies: Hypogammaglobulinemia (reduced immunoglobulin G/IgG levels) leading to frequent respiratory and other infections.

Blood and heart issues: Abnormal blood clotting/coagulation factors and occasional heart muscle weakness.

Hearing and vision: Sensorineural hearing loss and crossed eyes (strabismus) in some cases.

Causes

Gene Mutations: Pathogenic variants or deletions occur in the ALG12 gene located on chromosome 22q13.33.

Enzyme Deficiency: The mutation causes a shortage or dysfunction of the mannosyltransferase enzyme encoded by ALG12.

Impaired Glycosylation: The abnormal enzyme fails to properly add mannose sugar molecules to the growing lipid-linked oligosaccharide chain, resulting in incomplete sugar chains and deficient modification of vital proteins and fats needed across multiple body systems

Developmental Impact: Intellectual disability, global developmental delay, and weak muscle tone (hypotonia).

Growth Issues: Failure to thrive, poor growth in infancy, and short stature.

Immune & Blood Complications: Low antibody/immunoglobulin levels (hypogammaglobulinemia) leading to frequent infections, alongside blood-clotting (coagulation) abnormalities

Diagnosis

Initial Screening: Blood tests analyze serum transferrin to check for abnormal N-linked glycan patterns.

Enzyme and Functional Testing: Measuring specific enzyme activity in blood or skin fibroblasts supports the biochemical defect.

Definitive Genetic Testing: Exome sequencing or targeted gene panels confirm pathogenic variants in the ALG12 gene

Neurological: Generalized hypotonia (weak muscle tone), developmental delay, and intellectual disability.

Immunological: Low immunoglobulin (IgG) levels leading to frequent infections.

Physical & Structural: Failure to thrive, microcephaly, distinct facial features, and male genital abnormalities.

Treatment

Developmental support: Physical, occupational, and speech therapy to help with developmental delays and low muscle tone (hypotonia).

Feeding support: Dietary adjustments, specialized high-calorie formulas, or feeding tubes (like a G-tube) to treat failure to thrive and feeding difficulties.

Infection control: Prompt treatment of frequent upper respiratory and other infections, which happen due to low immune globulin levels.

Seizure control: Standard anti-seizure medications prescribed and monitored by a neurologist for patients who experience seizures.Cardiac and skeletal monitoring:

Type of Doctor Department : A medical geneticist (clinical geneticist) or a metabolic specialist (biochemical geneticist)

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