Metachromatic leukodystrophy (MLD) is a rare genetic disorder that affects the nervous system. It is caused by a deficiency of the enzyme arylsulfatase A, which leads to the accumulation of fatty substances called sulfatides in the brain and other tissues. This buildup damages the protective covering of nerve fibers, known as myelin, resulting in progressive neurological decline. Symptoms of MLD can vary but often include difficulties with movement, speech, and coordination. The condition typically manifests in childhood, but there are also late-onset forms. Diagnosis is usually confirmed through genetic testing and enzyme activity assays, and while there is currently no cure, supportive therapies can help manage symptoms.