Canadian researchers proposed that DNA sequencing followed by a dried blood spot acid alpha-glucosidase activity assay represents the best method for diagnosing Pompe disease, in view of the widespread availability of molecular testing, according to a study published in the Journal of Clinical Medicine.
“Pompe disease is an autosomal recessive disorder caused by pathogenic variants in the GAA gene, which encodes an acid alpha-glucosidase enzyme,” the authors of the study explained. The most common method for Pompe disease screening is the collection of dried blood spots, which are used to measure alpha-glucosidase activity.
Thus far, this has been viewed as an affordable and quick screening test. However, in recent years, the authors of this study have observed a paradigm shift away from dried blood spot testing towards targeted and whole gene-exome sequencing.
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Why is this the case? The cost of sequencing technologies has fallen, making it a much more viable option than before. It is also more accurate, allowing physicians to make a clear diagnosis of Pompe disease when alternative diagnoses are just as likely and cannot be ruled out. When measuring alpha-glucosidase activity through dried blood spots, pseudodeficiency alleles can cause false-positive results; hence, sequencing analysis of the GAA gene would still be needed to confirm the diagnosis.
Researchers decided to compare the 2 diagnostic methods in a clinical trial. First, they carried out clinical molecular testing on 2030 undiagnosed patients (both pediatric and adult) with a suspected muscular disorder. Second, the patients underwent dried blood spot testing to test their alpha-glucosidase enzyme levels. Blood samples were also collected to perform a clinical gene panel test, which included the GAA gene for Pompe disease.
Fourteen of the 2030 patients (0.69%) were diagnosed with Pompe disease through molecular analysis. Using dried blood spot testing, results of alpha-glucosidase activity were available for 1430 of the 2030 patients (70.4%). Of these 1430 patients, 58 patients (4.1%) recorded a decrease in alpha-glucosidase activity. When the threshold enzymatic activity for Pompe disease was set at 65% of the lower reference limit, 23 patients were found to have Pompe disease.
The authors of the study wrote, “Our study provides a direct comparison between results of sequencing and enzymatic activity measurement.” Given the value of both methods as seen in this study, the authors proposed a “combined approach” integrating both methods to screen for Pompe disease.
Thuriot F, Gravel E, Hodson K, et al. Molecular diagnosis of Pompe disease in the genomic era: correlation with acid alpha-glucosidase activity in dried blood spots. J Clin Med. 2021;10(17):3868. doi:10.3390/jcm10173868