Evidence Regarding Metachromatic Leukodystrophy Newborn Screening.

Metachromatic leukodystrophy (MLD) is a lysosomal disorder affecting approximately 1 per 100 000 newborns. It is caused by biallelic variations in the arylsulfatase A (ARSA) gene, leading to deficiency of ARSA enzyme activity and elevation of sulfatides. Most affected individuals have the late-infantile or early-juvenile phenotype, associated with significant and progressive neurologic degeneration and death. For these phenotypes, treatment with a lentiviral gene therapy in infancy can improve survival and motor function. However, in the absence of screening or an affected older sibling, most cases are diagnosed much later. A 2-tiered newborn screen, based on the presence of elevated sulfatides in dried blood spots followed by finding low ARSA enzyme activity, can accurately identify newborns with the early-onset phenotypes of MLD for timely gene therapy. An MLD screening study with consent is ongoing in 8 hospitals in New York City, and population-based newborn screening has been implemented in several regions in Europe. Although the false-positive rate is low, only 1 of these MLD newborn screening activities, in Hannover, Germany, has reported identifying cases. At least 4 newborn screening programs in the United States are in the process of implementing MLD screening.