Digital Microfluidics in Newborn Screening for Mucopolysaccharidoses: A Progress Report

Abstract

Newborn screening (NBS) for mucopolysaccharidosis type I (MPS I, Hurler syndrome) is currently conducted in about two-fifths of the NBS programs in the United States and in a few other countries. Screening is performed by measurement of residual activity of the enzyme alpha-l-iduronidase in dried blood spots using either tandem mass spectrometry or digital microfluidic fluorometry (DMF). In this article, we focus on the development and practical experience of using DMF to screen for MPS I in the USA. By means of their responses to a questionnaire, we determined for each responding program that is screening for MPS I using DMF the screen positive rate, follow-up methods, and classification of confirmed cases as either severe or attenuated. Overall, the results show that at the time of reporting, over 1.3 million newborns in the US were screened for MPS I using DMF, 2094 (0.173%) of whom were screen positive. Of these, severe MPS I was confirmed in five cases, attenuated MPS I was confirmed in two cases, and undetermined phenotype was reported in one case. We conclude that DMF is an effective and economical method to screen for MPS I and recommend second-tier testing owing to high screen positive rates. Preliminary results of NBS for MPS II and MPS III using DMF are discussed.

Evaluation, in a highly specialised enzyme laboratory, of a digital microfluidics platform for rapid assessment of lysosomal enzyme activity in dried blood spots

“…The advantages and limitations of DMF have been described previously 25–27 . In our experience, this innovative method is notably more rapid than existing assays employed in enzyme laboratories, such as ours.…”

“…The advantages and limitations of DMF have been described previously. [25][26][27] In our experience, this innovative method is notably more rapid than existing assays employed in enzyme laboratories, such as ours. Furthermore, DMF requires approximately 4000-fold less volume of sample and reagents than the methods used in our Enzyme Unit.…”

Harmonization of Newborn Screening Results for Pompe Disease and Mucopolysaccharidosis Type I

“…DMF has a short assay time starting with a 30-minute extraction phase and then incubation of the analytical cartridge [ 40 ]. The three-hour analysis time for each cartridge after sample preparation [ 20 ] gives DMF an advantage over the MS/MS platform, which requires further processing and analysis after incubation is complete. Shorter assay times equate to faster results and faster reporting, thereby facilitating a quicker diagnosis and subsequent intervention for affected infants [ 20 , 30 , 41 ].…”

“…Consequently, some programs report more false-positive results than others [ 10 , 17 ]. False-positive reports, which also contribute to parental anxiety [ 11 , 12 , 14 , 18 ] and over utilization of health care systems [ 1 ], can be reduced by way of second-tier assays, such as measuring the level of glycosaminoglycans (GAGs) for MPS I [ 19 , 20 , 21 ], evaluating the ratio of GAA activity to creatine/creatinine for PD [ 16 , 22 ], and using post-analytical tools such as Collaborative Laboratory Integrated Reports (CLIR) developed by the Mayo Clinic [ 15 , 20 , 23 ].…”

“…Our objective in this study was to harmonize enzyme activities for PD and MPS I analyzed using Digital Microfluidics (DMF) or Tandem Mass Spectrometry (MS/MS) across laboratories by two methods: using quality controls and regression equations, and MoM. Detailed descriptions of DMF and MS/MS lysosomal disorders (LD) screening have been described elsewhere [ 20 , 30 , 31 , 32 , 33 ]. We wanted to determine whether the same outcomes would be achieved: the correct identification of specimens exhibiting low or deficient activities (positive cases) and specimens exhibiting normal activities (negative cases).…”