Enzymatic and molecular strategies to diagnose Pompe disease

Abstract

Enzyme replacement therapy for Pompe disease, a neuromuscular disorder characterized by lysosomal glycogen storage due to acid α-glucosidase deficiency, has entered the clinic. There is more than ever a need for early and reliable diagnosis. The objective of this review is to present a critical review of the recent literature on laboratory procedures to diagnose Pompe disease by enzymatic assay and DNA analysis. The methods we used were Compilation and expert interpretation of recent and relevant publications. The introduction of new and the updating of existing laboratory procedures have facilitated the diagnosis of Pompe disease (glycogen storage disease type II; acid maltase deficiency; OMIM 232300). With regard to enzymatic analysis, the application of acarbose as inhibitor of maltase-glucoamylase has enabled the use of mixed leukocyte preparations as diagnostic material. The use of glycogen as a natural substrate in the reaction mixture adds to the selectivity of this procedure. Newborn screening is envisaged and facilitated by the introduction of high-throughput procedures. DNA analysis has become an integral part of the diagnostic procedure for confirmation and completion, for carrier detection, and for genetic counseling.

Rapid Ultraperformance Liquid Chromatography–Tandem Mass Spectrometry Assay for a Characteristic Glycogen-Derived Tetrasaccharide in Pompe Disease and Other Glycogen Storage Diseases

“…Therefore, this assay can be used for a presumptive diagnosis, but cannot serve as a diagnostic tool for differentiation between the various types of GSD. It should be followed by conventional enzymology for confirmation (24 ).…”

The Initial Evaluation of Patients After Positive Newborn Screening: Recommended Algorithms Leading to a Confirmed Diagnosis of Pompe Disease

“…2,[27][28][29] A molecular test is needed to confirm the diagnosis made by GAA activity. 4,24,26,29,30 It is important to note that enzymatic analysis, for example, in lymphocytes, is generally less specific than results obtained with skin fibroblasts, and so there can be a "gray zone" of enzyme activity where one cannot differentiate classic IOPD from LOPD.…”

“…by guest on July 8, 2020 www.aappublications.org/news Downloaded from Skin fibroblasts also allow for determination of the cross-reactive immunologic material (CRIM) status. 4,24,26 However, with the availability of molecular testing and its ability to predict CRIM status, the skin fibroblast assay is not needed in most cases. Skin biopsy should only be considered as a second-tier diagnostic tool when indeterminate results have been obtained by other methods and when a patient has 1 variant and low enzyme activity in blood and assay of enzyme activity in another tissue is needed to confirm a diagnosis.…”

“…The related risks associated with the need for anesthesia also must be considered, particularly in infants who have classic IOPD. 4,24,26 Because of the variable and heterogeneous muscle involvement, muscle histology cannot be used as a sole method of diagnosis, particularly for the juvenile or adult patient in whom the extent of glycogen accumulation is less and more variable than in the patient with IOPD. 26,29 If muscle biopsies are done, it is important that they are handled by laboratories with experience with Pompe disease and with capabilities to perform appropriate histologic analyses and recognize potential hallmarks of the disorder, 31…”

“…In cases of classic IOPD, prediction of CRIM status is possible with genotyping alone in close to 92% cases. 4,5,24,37 The nature and site of the 2 variants in the GAA gene typically predict a patient's clinical course. Sometimes, only 1 previously identified variant is found coupled with a novel, unclassified sequence VUS, thus complicating the diagnosis of Pompe disease.…”