Metachromatic leukodystrophy

Metachromatic leukodystrophy is a genetic disorder that affects the formation of myelin.  If both parents carry the gene, there is a 1 in 4 chance each of their children will contract the illness (autosomal recessive).  The illness can present at any age, and the earlier it presents, the faster its progression.
In infants, the disease will usually manifest between the ages of 18 & 24 months as difficulty walking, muscle wasting and weakness, developmental delays, loss of vision and convulsions eventually leading to paralysis, dementia and death generally before the first decade.
In teh juvenile from fo the disease, the disease usually starts with difficulty keeping up in school, followed by mental deterioration and dementia.  The symptoms that affect younger children then present themselves, but much more slowly.  However, most patients who develop the disease at this stage die in their second or third decade.
In adults, the disease almost always presents as a form of mental illness.  In adults, the symptoms progress very slowly and may last for more than a decade.
There is no treatment for any form of the disease, so care concentrates on alleviating some of the worse symptoms.  
The condition is not terribly uncommon, and is very common in certain isolated groups.  For example, in Israeli Jews of South Arabian extraction, it is as high as 1 in 76 people, and of Arabs living in Israel, it is 1 in 8,000.  In the general population, the incidence is somewhere between 1 in 40,000 and 1 in 160,000.
Metachromatic leukosystrophy at Wikipedia
MLD Foundation
Category:Genetics