ARSA is the gene listed for this condition in the packet. According to expert review, MLD results from reduced arylsulfatase A enzyme activity, and the condition is inherited in an autosomal recessive manner. Parents of an affected child are described as presumed heterozygous carriers, and heterozygous carriers are described as asymptomatic.

The review describes three classes of ARSA alleles that reduce enzyme activity: pathogenic variants that cause MLD, sequence variants that result in pseudodeficiency, and alleles carrying two sequence variants on the same chromosome. Alleles that produce no detectable functional enzyme are described as being associated with the early-onset late-infantile form, whereas alleles that retain some residual enzyme activity are associated with later-onset forms. For juvenile-onset MLD, the review describes affected individuals as often being compound heterozygous for one allele producing no functional enzyme and one allele with residual activity. The review describes substantial limitations in using these correlations to predict presentation and natural history, with considerable phenotypic variability implicating other genetic or environmental factors.

According to expert review, MLD is described as suspected in individuals with progressive neurologic dysfunction, which may first present as behavioral or motor signs and can occur at any age beyond one year following a period of normal development. A second suggestive finding is a leukodystrophy pattern on brain MRI, described as diffuse, symmetric periventricular myelin abnormalities, often with a tigroid pattern.

A third suggestive finding is deficient arylsulfatase A enzyme activity in leukocytes, described as less than 10% of normal controls in the usual synthetic-substrate assay. The review states that decreased enzyme activity alone is not sufficient for the diagnosis, because enzyme pseudodeficiency, in which activity is described as roughly 5% to 20% of normal controls in an otherwise healthy individual, is difficult to distinguish from true deficiency by biochemical testing alone.

The review describes phenotypes with notable overlap, including multiple sulfatase deficiency and saposin B deficiency, as well as other progressive degenerative disorders that appear after a period of normal development. On newborn screening, the review states that screening for MLD is under consideration because of therapeutic advances, that pseudodeficiency complicates this approach, and that a two-tier dried blood spot algorithm using a sulfatide measurement followed by enzyme activity has been developed. The packet does not certify a core or secondary newborn screening designation.

The packet does not record any FDA-approved treatments for this condition. The only orphan drug record, for recombinant human arylsulfatase A, carries a withdrawn status and is not a current option.

According to expert review, hematopoietic stem cell transplantation (HSCT) is an available therapy that attempts to address the primary central nervous system manifestations of MLD, using either donor-derived cells (allogeneic) or gene-modified cells from the affected individual (autologous). The review describes HSCT as unsuitable for individuals with significant neurologic involvement at the time of evaluation, and describes allogeneic transplantation as remaining controversial because outcome data are limited, vary by eligibility criteria and protocols, and differ across MLD types. For juvenile and adult MLD, the review states that the data support HSCT as a relatively safe procedure in pre- and early-symptomatic individuals, with disease stabilization described. It describes motor and cognitive function at evaluation as good predictors of outcome, and states that HSCT is not expected to fully abrogate the manifestations of the disease.

The review also describes an autologous gene-modified HSCT product, atidarsagene autotemcel, as showing sustained benefits in children with early-onset MLD; the packet does not record it as an FDA-approved treatment.

For ongoing management, the review describes evaluations across neurologic, developmental, neurobehavioral and psychiatric, hearing, vision, musculoskeletal, feeding and nutrition, gastrointestinal, respiratory, and family support domains. Some of these, such as motor function, developmental progress, and feeding, are described as assessed at each visit, whereas brain MRI and eye examinations are described as scheduled according to clinical indication or rate of progression.

According to expert review, the disease course may span several years in the late-infantile form and decades in the juvenile and adult forms. The review states that all individuals eventually develop complete loss of motor, sensory, and cognitive functions, and that death most commonly results from pneumonia or other infection. Life span is described as correlating roughly with age of onset but as quite variable, particularly in later-onset forms. The review also states that presenting symptoms appear to correlate with the rate of progression, with motor symptoms associated with faster deterioration than cognitive symptoms.

Several certified active trial records are present for this condition. Examples include NCT04283227, a Phase 3 record titled as OTL-200 in patients with late juvenile MLD (active, not recruiting; Orchard Therapeutics); NCT07046338, a record titled as lentiviral hematopoietic stem cell gene therapy for MLD (not yet recruiting; Shenzhen Geno-Immune Medical Institute); NCT03047369, a recruiting biorepository record for myelin disorders (Children's Hospital of Philadelphia); and NCT03655223, a record titled as expanded screening in newborns (active, not recruiting; RTI International). Record titles do not establish what an intervention does or whether it is effective. According to expert review, in vivo gene therapy using viral vectors delivered intrathecally or intracerebrally is under investigation, while enzyme replacement therapy has largely been considered impractical because of the difficulty of crossing the blood-brain barrier. Active clinical trials for this condition are listed on ClinicalTrials.gov.