My own definition (which is not fully descriptive). For technically correct definitions see below or research NIH, United leukodystrophy Foundation or www.MLDfoundation.org
The brain has a bunch of nerves that send signals to all parts of the body telling it to respond in all manner of ways depending on external or internal signals received. If you think of it as electrical wires you can image that wiring needs to be properly laid out and protected by insulation in order to function properly. All so that when you flip a light switch the proper signal goes from the signals point of origin (light switch) and connects the source of power (for this description let's say the circuit breaker box) and to the destination (light) with the correct power and instruction to power up the light. The transmission of that signal is protected by the sheathing (insulation) on the wiring. If there were a kink or break in the wiring, or it was wired incorrectly, the message may either not be delivered at all, be delayed, or be delivered incorrectly (perhaps the ceiling fan goes on instead). There could also be other outcomes including a fire.
What everyone thinks is a simple task, for instance walking, is actual made up of many complex tasks which are required to be made in rapid succession. Simply put, walking entails shifting balance from one leg to the other, lifting one leg, bending the toes, knee and ankle and moving it foward about 2 feet, planting the foot and re-balancing your body weight. Then lifting the alternate leg and bending the toes, knee and ankle and moving it foward while re-balancing the body.
MLD causes the myelin shield to deteriorate. And since this acts as an insulation to the nerve (i.e. wire), the receiving and transmitting of messages is compromised. Hence, symptoms and behaviors as defined in the descriptions below present themselves.
Brief Description from Kennedy Krieger Institute.
The brain has a bunch of nerves that send signals to all parts of the body telling it to respond in all manner of ways depending on external or internal signals received. If you think of it as electrical wires you can image that wiring needs to be properly laid out and protected by insulation in order to function properly. All so that when you flip a light switch the proper signal goes from the signals point of origin (light switch) and connects the source of power (for this description let's say the circuit breaker box) and to the destination (light) with the correct power and instruction to power up the light. The transmission of that signal is protected by the sheathing (insulation) on the wiring. If there were a kink or break in the wiring, or it was wired incorrectly, the message may either not be delivered at all, be delayed, or be delivered incorrectly (perhaps the ceiling fan goes on instead). There could also be other outcomes including a fire.
What everyone thinks is a simple task, for instance walking, is actual made up of many complex tasks which are required to be made in rapid succession. Simply put, walking entails shifting balance from one leg to the other, lifting one leg, bending the toes, knee and ankle and moving it foward about 2 feet, planting the foot and re-balancing your body weight. Then lifting the alternate leg and bending the toes, knee and ankle and moving it foward while re-balancing the body.
MLD causes the myelin shield to deteriorate. And since this acts as an insulation to the nerve (i.e. wire), the receiving and transmitting of messages is compromised. Hence, symptoms and behaviors as defined in the descriptions below present themselves.
Brief Description from Kennedy Krieger Institute.
Metachromatic leukodystrophy (MLD), the most common form of leukodystrophy, is a rare inherited neurometabolic disorder affecting the white matter of the brain (leukoencephalopathy). It is characterized by the accumulation of a fatty substance known as sulfatide (a sphingolipid) in the brain and other areas of the body (i.e., liver, gall bladder, kidneys, and/or spleen). The fatty protective covering on the nerve fibers (myelin) is lost from areas of the central nervous system (CNS) due to the buildup of sulfatide. Symptoms of metachromatic leukodystrophy may include convulsions, seizures, personality changes, spasticity, progressive dementia, motor disturbances progressing to paralysis, and/or visual impairment leading to blindness.
Abbreviated description from NIH:
What is Metachromatic Leukodystrophy?
Metachromatic leukodystrophy (MLD) is one of a group of genetic disorders called the leukodystrophies. These diseases impair the growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers. Myelin, which lends its color to the white matter of the brain, is a complex substance made up of at least 10 different enzymes. The leukodystrophies are caused by genetic defects in how myelin produces or metabolizes these enzymes. Each of the leukodystrophies is the result of a defect in the gene that controls one (and only one) of the enzymes. MLD is caused by a deficiency of the enzyme arylsulfatase A. MLD is one of several lipid storage diseases, which result in the toxic buildup of fatty materials (lipids) in cells in the nervous system, liver, and kidneys. There are three forms of MLD: late infantile, juvenile, and adult. Onset of the late infantile form (the most common MLD) is typically between 12 and 20 months following birth. Affected children have difficulty walking after the first year of life. Symptoms include muscle wasting and weakness, muscle rigidity, developmental delays, progressive loss of vision leading to blindness, convulsions, impaired swallowing, paralysis, and dementia. Children may become comatose. Most children with this form of MLD die by age 5. The juvenile form of MLD (between 3-10 years of age) usually begins with impaired school performance, mental deterioration, and dementia and then develop symptoms similar to the infantile form but with slower progression. The adult form commonly begins after age 16 as a psychiatric disorder or progressive dementia. Symptoms include impaired concentration, ataxia, seizures, dementia, and tremor..
Is there any treatment?
There is no cure for MLD. Bone marrow transplantation may delay progression of the disease in some cases. Other treatment is symptomatic and supportive. Considerable progress has been made with regard to gene therapy in an animal model of MLD.
What is the prognosis?
The prognosis for MLD is poor. Most children within the infantile form die by age 5. Symptoms of the juvenile form progress with death occurring 10 to 20 years following onset. Those persons affected by the adult form typically die withing 6 to 14 years following onset of symptoms.
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