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Glossary

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L

Lafora’s disease: 

A progressive myoclonic encephalopathy (PME) that is inherited as an autosomal recessive trait. Associated symptoms typically begin in childhood or early adolescence and include frequent seizures characterized by loss of consciousness and rhythmic contraction and relaxation of all muscle groups (generalized tonic-clonic seizures); sudden, involuntary, “shock-like” muscle jerks (myoclonus); and rapidly progressive deterioration of thought processing and acquired intellectual abilities (dementia). Removal and microscopic examination of minute tissue samples (e.g., muscle fibers, liver cells, etc.) reveal abnormal, characteristic deposits of complex proteins and carbohydrates within the fluid portion of cells (intracytoplasmic inclusions known as “Lafora bodies”). 

: Also known as “posthypoxic” or “postanoxic action myoclonus,” this condition is characterized by the development of chronic action myoclonus due to a temporary lack or inadequate supply of oxygen to the brain (cerebral hypoxia or anoxia). Patients with action myoclonus experience sudden, involuntary, “shock-like” muscle contractions that may be triggered or aggravated by voluntary movement. Lance-Adams syndrome is also often associated with cerebellar ataxia or lack of coordination, postural imbalance, and other associated findings.

Lance-Adams syndrome: 

Lateral: 

Sideways; of, on, from, or toward the side.

Leigh disease: 

A disorder of mitochondrial function that typically becomes apparent during infancy. Also known as subacute necrotizing encephalomyelopathy, the disorder may be characterized by feeding and swallowing difficulties, vomiting, muscle weakness, low muscle tone (hypotonia), and delayed acquisition of motor and language skills. Affected infants and children may also develop seizures; an impaired ability to coordinate voluntary movements (ataxia); involuntary, rapid, rhythmic eye movements (nystagmus); tremor; dystonia; and/or other abnormalities. The disorder, which has a number of underlying causes, may occur randomly for unknown reasons (sporadically) or be transmitted as an autosomal recessive or X-linked trait. Leigh disease is associated with characteristic changes of the central nervous system (CNS), including symmetric regions of localized tissue loss (necrosis) and neurodegenerative changes of the basal ganglia, thalamus, brainstem, spinal cord, and other regions of the CNS.

Leucine: 

an essential amino acid.

Implantable Pulse Generator (IPG):

A device that is placed under the skin near the collarbone as part of a surgical procedure known as deep brain stimulation. Wire leads from electrodes implanted in the brain are connected to the pulse generator, which then delivers continuous high frequency electrical stimulation to the thalamus via the implanted electrodes. This form of stimulation probably “jams” the nucleus and therefore modifies the message in the movement control centers of the brain, serving to suppress tremor.

Lewy body: 

A Lewy body is a mass of protein found in dying nerve cells in the brain.

Lewy Body Disease: 

Also called diffuse Lewy body disease, Lewy body dementia. Lewy body disease is a common cause of dementia, accounting for approximately 15%-20% of all cases. The age of onset is typically in the late 50s through the 70s. It is more common in men than women. Lewy Body Disease is characterized by more daily fluctuations in symptoms than Alzheimer’s disease, as well as more prominent psychosis. Patients are prone to have adverse reactions to antipsychotics. Patients also have parkinsonian features early in the disease, including slowed movements and rigidity, though usually without tremor. The Lewy body is a protein aggregate found in dying neurons in the brain. In Lewy body disease, the Lewy bodies are most prominently found in the cortex, or surface of the brain, versus in the midbrain for Parkinson’s disease.

Lipopolysaccharide:

A lipopolysaccharide is a molecule made up of a lipid (a fat) with a polysaccharide (a complex sugar). In most circumstances, the terms lipopolysaccharide and endotoxin can be used interchangeably.

Lumbar puncture: 

A procedure during which a sample of fluid (i.e., cerebrospinal fluid [CSF]) is removed from the spinal canal for diagnostic or therapeutic purposes. During the procedure, CSF is obtained via a hollow needle inserted between two bones of the spinal column within the lower back (i.e., usually the third and fourth lumbar vertebrae). Laboratory analysis conducted on CSF may help to diagnose central nervous system infections, certain tumors, or particular neurologic disorders. In some cases, lumbar puncture may also be performed to inject certain medications into the CSF, such as particular anticancer (chemotherapeutic) agents.

Lysosomal: 

Referring to lysosomes, which are membrane-bound bodies (organelles) outside the nuclei of cells that contain various enzymes engaged in intracellular digestion.

Lysosomal storage diseases: 

Inborn errors of metabolism in which deficiency or impaired functioning of particular lysosomal enzymes leads to an abnormal accumulation of certain substances (e.g., fats, complex carbohydrates) within particular cells, progressively affecting multiple bodily tissues and organs. (Lysosomes are membrane-bound, enzyme-containing bodies within cells that engage in digestive processes; enzymes are proteins that accelerate the rate of certain chemical reactions in the body.) Most lysosomal storage disorders (e.g., mucolipidoses, mucopolysaccharidoses, lipidoses, etc.) are thought to be inherited as autosomal recessive traits.