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

Abstract

Newborn screening (NBS) for Pompe disease is done through analysis of acid α-glucosidase (GAA) activity in dried blood spots. When GAA levels are below established cutoff values, then second-tier testing is required to confirm or refute a diagnosis of Pompe disease. This article in the "Newborn Screening, Diagnosis, and Treatment for Pompe Disease" guidance supplement provides recommendations for confirmatory testing after a positive NBS result indicative of Pompe disease is obtained. Two algorithms were developed by the Pompe Disease Newborn Screening Working Group, a group of international experts on both NBS and Pompe disease, based on whether DNA sequencing is performed as part of the screening method. Using the recommendations in either algorithm will lead to 1 of 3 diagnoses: classic infantile-onset Pompe disease, late-onset Pompe disease, or no disease/not affected/carrier. Mutation analysis of the gene is essential for confirming the biochemical diagnosis of Pompe disease. For NBS laboratories that do not have DNA sequencing capabilities, the responsibility of obtaining sequencing of the gene will fall on the referral center. The recommendations for confirmatory testing and the initial evaluation are intended for a broad global audience. However, the Working Group recognizes that clinical practices, standards of care, and resource capabilities vary not only regionally, but also by testing centers. Individual patient needs and health status as well as local/regional insurance reimbursement programs and regulations also must be considered.

Moonlighting newborn screening markers: the incidental discovery of a second-tier test for Pompe disease

“…Another benefit of a reliable biochemical second-tier test is the avoidance of anxiety and costs associated with the frequent discovery of genotypes of uncertain significance, which eventually turn out to be unaffected individuals with pseudodeficient GAA activities. 8,34,35 It is also possible to begin exploring whether the Cre/Crn ratio alone, the (Cre/Crn)/GAA ratio, or additional permutations of ratios could be relevant to the expansion of the biochemical phenotype of other conditions with prominent skeletal and cardiac myopathy and consequent elevation of creatinine phosphokinase, for example, very long chain fatty acid oxidation disorders 36 and particularly DMD and related disorders. 37 For proof of concept, preliminary testing of blood spotted on filter paper from residual clinical samples of genotyped DMD patients showed consistent elevations of the Cre/Crn ratio ( Figure 3; age 3-11 years, N = 10, range 6.42-8.99; age 25-39 years, N = 10, range 4.71-10.44; controls of age 21-60 years, N = 11, range 2.55-4.96; see Table 1 for neonatal reference percentiles).…”

What Genomic Sequencing Can Offer Universal Newborn Screening Programs

“…In some U.S. states, sequencing is already used as a follow‐up test in newborns who have screened positive for certain conditions on initial or first‐tier newborn screening tests. For conditions like cystic fibrosis and lysosomal storage disorders, sequencing can help to confirm a diagnosis and can provide additional prognostic information . For nonspecific disorders, such as immunodeficiencies and hearing loss, gene panels or whole‐exome sequencing can help determine the underlying cause of the condition, information that is critical for appropriate medical management, surveillance, and treatment .…”

“…For conditions like cystic fibrosis 2 and lysosomal storage disorders, 3 sequencing can help to confirm a diagnosis and can provide additional prognostic information. 4 For nonspecific disorders, such as immunodeficiencies and hearing loss, gene panels or whole-exome sequencing can help determine the underlying cause of the condition, information that is critical for appropriate medical management, surveillance, and treatment. 5 In the future, widespread use of sequencing as a diagnostic follow-up to existing screening tests could also decrease the number of false positives generated in public health programs, thereby lessening the emotional and financial burden on parents and the health care system.…”

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

“…Most early onset cases are symptomatic in some form at birth. Two NBS algorithms for diagnostic confirmation have been developed by a group of international experts on both NBS and PD, the Pompe Disease Newborn Screening Working Group, based on whether DNA sequencing is performed as part of the screening algorithm [6]. Applying the recommendations of either algorithm can lead to a diagnostic characterization as: (a) classic IOPD, (b) "predicted" LOPD, or (c) no disease/not affected/carrier.…”

“…Applying the recommendations of either algorithm can lead to a diagnostic characterization as: (a) classic IOPD, (b) "predicted" LOPD, or (c) no disease/not affected/carrier. In both algorithms, a variety of clinical tests are necessary to confirm the diagnosis and generate a treatment plan, including DNA sequencing, since the GAA gene variant analysis is essential for confirming the diagnosis and developing a treatment strategy of PD [6]. A challenge to pursuing DNA sequencing as part of NBS algorithms is that many NBS PHLs and clinical referral centers do not perform or have ready access to sequencing resources on premises.…”