Proteomic analysis of dried blood spots and buccal swabs were helpful at discriminating between Pompe disease and its pseudodeficiencies as a second-tier screening method, as presented at the 18th Annual WORLDSymposium 2022.
The authors found that direct quantification of endogenous acid alfa-glucosidase (GAA) could be used to help differentiate between true positive cases of Pompe disease and pseudodeficiencies, and the method was also applied to mucopolysaccharidosis type 1 (MPS 1).
“Pompe disease and MPS 1 have high false positive rates on [newborn screening] due to high prevalence of pseudodeficiencies,” the authors said. Using the immunoaffinity enrichment coupled to selected reaction monitoring with mass spectroscopy method, they were able to quantify the levels of GAA for patients with Pompe disease and alpha-L-iduronidase (IDUA) from dried blood spots and buccal swabs.
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The GAA levels present in controls (n=22) ranged from 124 pmol/L to 421 pmol/L (244.5±90.3 pmol/L) which was higher than patients with pseudodeficiency of Pompe disease (n=8) which had values ranging from 41 pmol/L to 208 pmol/L (113.5 ±54.6 pmol/L). Pompe disease carriers had similar levels to pseudodeficiency with values ranging from 42 pmol/L to 157 pmol/L (114.7±37.1 pmol/L).
Patients with Pompe disease had levels much lower than the 1 treatment-naïve patient with infantile-onset Pompe disease (IOPD) having nondetectable levels of the peptide. Patients with late-onset Pompe disease (LOPD) had levels ranging from 0 pmol/L to 66 pmol/L (22.3±20.7 pmol/L). Of these patients with LOPD, 1 with a homozygous c.-31-13 T mutation had the highest levels.
“Notably, milder forms such as [LOPD] and attenuated MPS I cases had distinguishably lower peptides in [dried blood spots] than carriers or pseudodeficiency cases,” the authors said. Analysis with buccal swabs also showed similar trends of decreasing GAA levels between controls, carriers, pseudodeficiency, and patients with Pompe disease. Patients with the more severe IOPD had lower levels than those with LOPD.
“Proteomic and enzymatic GAA and IDUA determinations in [buccal swabs] were similarly informative to predict the phenotypes of the [Pompe disease] and MPS I. Buccal swab could serve as an alternative sample resource,” the authors concluded.
Sun A, Zhang T, Duong P, et al. A rapid and non-invasive proteomic analysis using DBS and buccal swab for multiplexed second-tier screening of Pompe disease and Hurler syndrome. Mol Genet Metab. 2022;135(2):S117-S118. doi:10.1016/j.ymgme.2021.11.312