Recommendations for Infantile-Onset and Late-Onset Pompe Disease: An Iranian Consensus

Background: Pompe disease, also denoted as acid maltase or acid α-glucosidase deficiency or glycogen storage disease type II, is a rare, autosomal recessive lysosomal storage disorder. Several reports have previously described Pompe disease in Iran and considering increased awareness of related subspecialties and physicians, the disease's diagnosis is growing.

Objective: This guideline's main objective was to develop a national guideline for Pompe disease based on national and international evidence adapting with national necessities.

Methods: A group of expert clinicians with particular interests and experience in diagnosing and managing Pompe disease participated in developing this guideline. This group included adult neurologists, pediatric neurologists, pulmonologists, endocrinologists, cardiologists, pathologists, and physiatrists. After developing search terms, four authors performed an extensive literature review, including Embase, PubMed, and Google Scholar, from 1932 to current publications before the main meeting. Before the main consensus session, each panel member prepared an initial draft according to pertinent data in diagnosis and management and was presented in the panel discussion. Primary algorithms for the diagnosis and management of patients were prepared in the panel discussion. The prepared consensus was finalized after agreement and concordance between the panel members.

Conclusion: Herein, we attempted to develop a consensus based on Iran's local requirements. The authors hope that disseminating these consensuses will help healthcare professionals in Iran achieve the diagnosis, suitable treatment, and better follow-up of patients with infantile-onset Pompe disease and late-onset Pompe disease.

Second Tier Molecular Genetic Testing in Newborn Screening for Pompe Disease: Landscape and Challenges

Pompe disease (PD) is screened by a two tier newborn screening (NBS) algorithm, the first tier of which is an enzymatic assay performed on newborn dried blood spots (DBS). As first tier enzymatic screening tests have false positive results, an immediate second tier test on the same sample is critical in resolving newborn health status. Two methodologies have been proposed for second tier testing: (a) measurement of enzymatic activities such as of Creatine/Creatinine over alpha-glucosidase ratio, and (b) DNA sequencing (a molecular genetics approach), such as targeted next generation sequencing. (tNGS). In this review, we discuss the tNGS approach, as well as the challenges in providing second tier screening and follow-up care. While tNGS can predict genotype-phenotype effects when known, these advantages may be diminished when the variants are novel, of unknown significance or not discoverable by current test methodologies. Due to the fact that criticisms of screening algorithms that utilize tNGS are based on perceived complexities, including variant detection and interpretation, we clarify the actual limitations and present the rationale that supports optimizing a molecular genetic testing approach with tNGS. Second tier tNGS can benefit clinical decision-making through the use of the initial NBS DBS punch and rapid turn-around time methodology for tNGS, that includes copy number variant analysis, variant effect prediction, and variant 'cut-off' tools for the reduction of false positive results. The availability of DNA sequence data will contribute to the improved understanding of genotype-phenotype associations and application of treatment. The ultimate goal of second tier testing should enable the earliest possible diagnosis for the earliest initiation of the most effective clinical interventions in infants with PD.