Newborn screening for metachromatic leukodystrophy: Preparation of reagents and methodology for measurement of sulfatides and arylsulfatase A enzymatic activity in dried blood spots.

Ex vivo gene therapy combined with haemapoietic stem cell transplant has recently been approved in Europe and the USA for treatment of metachromatic leukodystrophy (MLD). Since treatment is only efficacious if carried out in the pre-symptomatic or minimally-symptomatic phases, newborn screening (NBS) for MLD is warranted. MLD NBS is being developed worldwide through the International MLD Newborn Screening Alliance. Screening is carried out by measurement of the elevation of two sulfatide molecular species, 16: 0- and 16:1-OH-sulfatide in dried blood spots (DBS) followed by second-tier measurement of arylsulfatase A (ARSA) enzymatic activity in the same DBS. After 2-3 years of NBS assay development including pilot studies, members of the International MLD Newborn Screening Alliance arrived at a consensus set of assay protocols. In this article, we provide these protocols with full details so that the methods can be readily adopted by additional NBS laboratories. We also provide the full details of preparation of the required reagents.