Metachromatic leukodystrophy (MLD) is an inherited disorder that affects the brain, spinal cord, and the peripheral nerves. This disorder is caused by a deficiency of the enzyme called arylsulfatase A, leading to a build up of fatty substances primarily in the cells of the nervous system, and progressive destruction of the white matter covering nerve fibers in the brain. The symptoms of MLD occur gradually in the individuals who previously appear healthy. Affected individuals have symptoms including progressive deterioration of intellectual functions and motor skills, loss of sensation in the extremities, seizures, paralysis, inability to speak, blindness, hearing loss, and eventually unresponsiveness. The age of onset varies from late infantile to adult. In the most common and severe form, symptoms begin between the ages of six months and two years and most affected children die by age 5. MLD progresses more slowly in the late onset forms and death varies from within 10 years to several decades after onset. There is no specific treatment available but medical surveillance and care may help to improve some symptoms and overall condition of life. One of the causes of MLD is pathogenic variants in the ARSA gene.