Symptoms of Batten disease and other NCLs are linked to a buildup of substances called lipofuscins (lipopigments) in the body's tissues. These lipopigments are made up of fats and proteins. Their name comes from the technical word lipo, which is short for "lipid" or fat, and from the term pigment, used because they take on a greenish-yellow color when viewed under an ultraviolet light microscope. The lipopigments build up in cells of the brain and the eye as well as in skin, muscle, and many other tissues. Inside the cells, these pigments form deposits with distinctive shapes that can be seen under an electron microscope. Some look like half-moons, others like fingerprints. These deposits are what doctors look for when they examine a skin sample to diagnose Batten disease.
The biochemical defects that underlie several NCLs have recently been discovered. An enzyme called palmitoyl-protein thioesterase has been shown to be insufficiently active in the infantile form of Batten disease (this condition is now referred to as CLN1). In the late infantile form (CLN2), a deficiency of an acid protease, an enzyme that hydrolyzes proteins, has been found as the cause of this condition. A mutated gene has been identified in juvenile Batten disease (CLN3), but the protein for which this gene codes has not been identified.
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