Metachromatic Leukodystrophy (MLD) is a rare genetic disorder where the enzyme arylsulfatase-A ("ARSA"), which normally breaks down the lipid sulfatide, is missing. The resulting build-up of sulfatide in the central nervous system and peripheral nervous system causes progressive loss of myelin. Normally, nerve endings are covered with a myelin sheath which helps speed the communication of nerve impulses and protects the underlying nerve cell. The accumulation of sulfatide causes the myelin to break down, affecting the patient's coordination, strength and cognition.
There are three types of MLD. The first is known as Late Infantile MLD, which generally appears between 6 months and 2 years of age. The child will develop normally until the onset of the disease, at which point parents will first begin to notice a change in gross motor skills. The child may be delayed in learning to walk, or begin to stagger and fall frequently. Eventually, the child will lose any abilities that she or he had once acquired, including speaking, moving and even swallowing.
The second type, Juvenile Form MLD, typically appears between ages 4 and 12. The disease first affects the ability to walk and the child's posture. Mentally, the child will have emotional difficulties, have trouble following directions, develop abnormal behaviors, and begin to experience academic difficulties.
Individuals with the third type, Adult Form MLD, will begin to show symptoms between the teenage years and 40. Cognitive and behavioral abnormalities appear first, often causing the disease to be misdiagnosed as schizophrenia or mental illness. The patient will display personality changes- appearing anxious, apathetic, disorganized, or bewildered- and demonstrate declining memory skills. Physically, they may become clumsier. The progression of Adult Form MLD follows the same pattern as Type 2, but at a slower rate.
Although the Late Infantile variant is particularly devastating, all forms of MLD if untreated will lead to neurologic deterioration and ultimately death.