Early-juvenile metachromatic leukodystrophy (MLD)

Most children are diagnosed after symptoms start. Early signs often involve walking, such as stumbling, or new trouble with attention or schoolwork. U.S. experts say the diagnosis needs two kinds of tests together. One is a gene test for changes in the ARSA gene. The other measures the enzyme (arylsulfatase A) and the fatty substances it breaks down (sulfatides).

Both kinds of test matter. Some healthy people have harmless gene changes (pseudodeficiency) that lower the enzyme result, so a low enzyme level alone can mislead. A brain MRI often shows the typical damage to the white matter, where the nerve coating is. Nerve tests (nerve conduction studies) can show damage to the nerves of the body. U.S. guidelines advise including a genetic counselor who knows MLD from the time of diagnosis.

In the past, most children found early enough for treatment were found because an older brother or sister was diagnosed first. U.S. guidelines advise testing both parents at diagnosis and testing brothers and sisters who could be affected. Newborn screening can also find MLD. In September 2025, New York became the first U.S. state to start screening all newborns for MLD, as a pilot program. In December 2025, MLD was added to the national list of recommended newborn screening conditions. Each state decides whether and when to start.

Atidarsagene autotemcel is a one-time gene therapy made from the child’s own blood-forming stem cells, with a working ARSA gene added in a lab. The cells are given back after strong chemotherapy (conditioning). For this form, it is approved before symptoms, or with early symptoms while the child can still walk alone and before thinking skills decline. It is sold as Libmeldy in the European Union (approved December 2020) and the UK, and as Lenmeldy in the United States (approved March 2024).

The studies behind the US approval were small. Of 7 children with this form treated before symptoms, 3 could be assessed, and all 3 were still walking on their own years later. Of 10 children treated after early symptoms, 8 later lost the ability to walk without support and 2 died as the disease got worse, though some kept normal thinking scores. These counts are about walking without support. The figures in the Outlook section use a different measure: losing both the ability to walk and the ability to sit without support, or death.

Risks include serious infections and a possible risk of blood cancer, so children need yearly checks, though no cases had been reported when the US label was written. In the studies, one child with this form died of a stroke caused by a blood clot, and another had brain inflammation (encephalitis). Half of the girls treated later had ovarian failure, meaning their ovaries stopped working.

A donor stem cell transplant has been used for some children with juvenile MLD found before symptoms or very early. US experts advise gene therapy first for this form where it is available, so a transplant is more likely to come up where it is not. Its benefit is more limited in the early-onset forms, and it carries its own serious risks.

For children with more advanced disease, care focuses on comfort and daily life. It can include physical therapy, feeding help, and medicines for seizures, pain and stiff muscles. School and family support are part of care.

Early-juvenile MLD is a serious condition. U.S. experts describe its pace and symptoms as similar to the late-infantile form. Survival in the juvenile forms varies. A 2025 expert review notes that people with juvenile-onset MLD often do not reach age 20.

Timing shapes the outlook more than anything else. Gene therapy and transplant work best before symptoms, or very early. Neither one undoes damage that has already happened. This is why brothers and sisters are tested quickly, and why newborn screening matters so much for this condition.

In long-term gene therapy studies, children with this form treated before symptoms or with early symptoms did far better than untreated children. The figures below come from small groups at specialist centers. They show what happened to those children, not what will happen to any one child.