GM1 gangliosidosis is an inherited metabolic condition caused by pathogenic variants (disease-causing changes) in both copies of the GLB1 gene. This condition follows an autosomal recessive inheritance pattern, meaning that an affected child inherits one altered copy of the gene from each parent.

The GLB1 gene provides instructions for producing an enzyme called beta-galactosidase (β-galactosidase). This enzyme plays an important role in breaking down complex molecules, particularly GM1 ganglioside, which is a type of glycolipid found in cell membranes and is especially abundant in nerve cells.

When both copies of the GLB1 gene contain disease-causing variants, beta-galactosidase activity becomes significantly reduced or absent. As a result, GM1 ganglioside cannot be broken down effectively and gradually accumulates inside lysosomes, which are specialised structures responsible for cellular waste processing.

This accumulation primarily affects neurons in the brain and spinal cord but can also involve other organs, including the liver, spleen and bones.

Progressive accumulation causes cellular dysfunction, neuronal damage and eventually cell death. This explains the progressive neurological deterioration and developmental regression observed in affected children.

How is it inherited within a family?

When both parents are carriers of a pathogenic GLB1 variant, each pregnancy has:
– 25% chance of having an affected child.
– 50% chance of having a child who is an unaffected carrier.
– 25% chance of having a child who is unaffected and not a carrier.
These probabilities remain the same for every pregnancy, regardless of the outcome of previous pregnancies.

Genetic counselling is important to explain recurrence risks and discuss reproductive options, including prenatal diagnosis and preimplantation genetic testing where appropriate.