What is the diagnostic workup for Lysosomal Storage Diseases (LSDs)?

From the Guidelines

The diagnostic workup for Lysosomal Storage Diseases (LSDs) should begin with a thorough clinical evaluation, followed by specific biochemical and genetic testing, including enzyme activity assays and biomarker analysis, as recommended by the American College of Medical Genetics and Genomics 1. The initial assessment includes a detailed medical history focusing on developmental delays, organomegaly, skeletal abnormalities, and neurological symptoms.

• Key points to consider in the clinical evaluation:
  • Developmental delays
  • Organomegaly
  • Skeletal abnormalities
  • Neurological symptoms Laboratory testing should include enzyme activity assays specific to the suspected LSD, such as measuring β-glucocerebrosidase for Gaucher disease or α-galactosidase A for Fabry disease, as outlined in the technical standard for measuring lysosomal enzyme activities 1.
• Enzyme assays can be performed on:
  • Blood leukocytes
  • Dried blood spots
  • Cultured fibroblasts Urinary glycosaminoglycan (GAG) analysis is essential for mucopolysaccharidoses, and biomarker testing, such as sphingosine in Krabbe disease, can help clarify variants of uncertain clinical significance and provide a baseline value 1. Genetic testing should follow to confirm the diagnosis by identifying pathogenic variants in the relevant genes.
• Additional investigations may include:
  • Imaging studies like MRI to assess neurological involvement
  • Echocardiography for cardiac manifestations
  • Ophthalmologic examination for ocular abnormalities
  • Bone marrow aspiration may be necessary for diseases like Gaucher to evaluate for characteristic storage cells Early diagnosis is crucial as enzyme replacement therapy, substrate reduction therapy, and other targeted treatments are available for many LSDs and are most effective when started before irreversible damage occurs, as highlighted in the study on biomarker testing for lysosomal diseases 1. Multidisciplinary management involving geneticists, neurologists, and metabolic specialists is recommended due to the complex, multisystemic nature of these disorders, and the importance of longitudinal biomarker analysis in patients to guide therapeutic intervention and/or response 1.

From the Research

Diagnostic Workup for Lysosomal Storage Diseases (LSDs)

The diagnostic workup for LSDs involves several steps, including:

• Clinical suspicion and evaluation, which is the first stage of diagnosis 2, 3, 4
• Enzyme activity assays, such as fluorometry and MS/MS methods, which are used to measure lysosomal enzyme activity 5, 2, 4
• Molecular examination, including techniques such as RFLP-PCR, ARMS-PCR, mutation scanning methods, DNA sequencing, MLPA, and NGS, which are used to confirm the diagnosis and identify the underlying genetic defect 2, 3, 4
• Newborn screening programs, which use methods such as fluorometric assays and MS/MS multiplex enzyme assays to detect LSDs in dried blood spot specimens 5, 4
• Prenatal diagnosis, which can be performed using enzymatic and molecular testing on chorionic villus sampling or amniotic fluid samples 2

Enzyme Activity Assays

Enzyme activity assays are an important part of the diagnostic workup for LSDs. These assays measure the activity of specific lysosomal enzymes and can help diagnose enzyme deficiencies. The major enzymatic testing methods include:

• Fluorometric assays using artificial 4-methylumbelliferyl (4-MU) substrates 5, 4
• Spectrophotometric assays 5
• Radioactive assays with radiolabeled natural substrates 5
• MS/MS or LC-MS/MS multiplex enzyme assays 5, 4

Molecular Examination

Molecular examination is used to confirm the diagnosis and identify the underlying genetic defect. The techniques used include:

• RFLP-PCR and ARMS-PCR 4
• Mutation scanning methods 4
• DNA sequencing 4
• MLPA and NGS methods 4 These techniques can help identify the specific genetic mutation responsible for the LSD and can be used for prenatal diagnosis and genetic counseling 2, 3