Diagnosis of GM1 gangliosidosis involves a combination of clinical evaluation, biochemical testing and molecular genetic analysis. Since the condition can present with symptoms that overlap with other lysosomal storage disorders, laboratory confirmation is essential.

1. Clinical evaluation

A paediatrician or clinical geneticist evaluates the child’s medical history, developmental milestones, neurological symptoms and physical features.

Important findings that may raise suspicion include:
– Hypotonia and developmental delay.
– Loss of previously acquired developmental skills.
– Hepatosplenomegaly.
– Coarse facial features.
– Skeletal abnormalities.
– Cherry-red spots on retinal examination.

2. Biochemical enzyme analysis

A key diagnostic investigation is measuring beta-galactosidase enzyme activity.

This is generally performed using a blood sample, particularly leukocytes (white blood cells), or other appropriate laboratory specimens.

In individuals with GM1 gangliosidosis, beta-galactosidase activity is significantly reduced or absent compared with the normal reference range.

This biochemical investigation provides important evidence of the underlying metabolic defect.

3. Molecular genetic testing

Genetic testing is performed to identify pathogenic variants in both copies of the GLB1 gene.

Testing may involve:
– Targeted GLB1 gene sequencing.
– Next-generation sequencing (NGS) panels for lysosomal storage disorders.
– Whole-exome sequencing (WES), when the diagnosis is uncertain.
– Deletion and duplication analysis if sequencing does not identify both disease-causing variants.
Identifying the specific variants helps establish the molecular diagnosis, determine the inheritance pattern and facilitate family testing.

4. Additional investigations

Other investigations may include:
– Ophthalmological examination to identify a cherry-red spot.
– Brain MRI to assess neurological involvement.
– Skeletal X-rays to identify characteristic bone abnormalities.
– Liver and spleen assessment.
Combining enzyme analysis with molecular genetic testing provides a reliable approach to confirming GM1 gangliosidosis and distinguishing it from other metabolic disorders.