Astrocytes: A type of glial cell in the brain commonly thought to provide structure, and nutritional support to nerve cells and oligodendrocytes. Scientists are realizing these cells likely have much more complex roles than previously thought, for example in their role in surrounding the blood vessels of the brain with extensions called podocytes, or feet important in certain leukodystrophies.

Ataxia: Problems with balance and coordination, usually caused by problems with the cerebellum and other brain stems regulating movement. This can be manifested by unsteadiness in walking and sitting or by difficulties with fine motor.control.

Dystonia: Increased tone in the muscles and joints caused by injury to the extrapyramidal system, a part of the brain responsible for modulating movement. Dystonia can result in abnormal postures and positions of the joints and extremities and if untreated can impair mobility and cause complications with the bones and joints.

Gene:  Genes are the code, or recipe in the body’s DNA to make a specific protein or building block of a cell.

Genetic Disorder: A genetic disorder is a disorder caused by a problem in the genes.

Glial Cell: The cells that help make up the white matter of the brain. Different types include oligodendrocytes, astrocytes and microglia. Together these cells help create a supportive environment in the brain, which helps nurture and structure the nerve cells or neurons.

Hypotonia: Low tone in the muscles of the arms, legs or trunk of the body, usually caused by injury to the parts of the brain regulating movement and strength.

Inherited: Most, though not all genetic disorders are inherited. An inherited disorder may be transmitted by both parents if two copies of the abnormal gene need to be present for disease (autosomal recessive inheritance).  In this case parents are considered carriers, or carrying a genetic change on only one gene but otherwise healthy. An inherited disorder may be transmitted by one parent if only one copy of the abnormal gene needs to be present for disease (autosomal dominant inheritance). Other inheritance patterns exist if the gene is on the X chromosome, in which case the disorder is usually passed along by a carrier mother (X linked inheritance). Another means of transmission is in the mitochondrial DNA, also transmitted by the mother. Please note that many disorders that affect the mitochondria are not transmitted through the mitochondrial DNA and are inherited in an autosomal recessive manner. Finally, it is important to note that some genetic disorders appear spontaneously in the affected individual and are not inherited. These are called sporadic.

Leukodystrophy: A genetic disorder, or a disorder caused by problems in the genes, resulting in a problem with the white matter of the brain. Read more about these disorders here.

Microglia: Very small glial cell thought to play a role in brain inflammation and immune surveillance.

Myelin: The insulation made by oligodendrocyte cells, which helps support the projections of the nerve cells in and out of the brain. Oligodendrocytes make this by producing certain specific lipids or fats and proteins, and then wrapping projections containing these substances around the projection of a nerve much like the layers of an onion.

Oligodendrocytes: A type of glial cell in the brain responsible for the production of myelin. They interact with neurons but also other glial cells such as astrocytes.  In many leukodystrophies, oligodendrocytes are either lost or injured.

Seizures: Seizures are the result of abnormal electrical activity in the brain, and may present with shaking of one or many extremities, brief jerk like movements, altered level of consciousness or abrupt changes in tone (stiffness or floppiness). Patients with many seizures are classified as having epilepsy.

Spasticity: Increased tone of the muscles, usually caused by an injury to the pyramidal system of the brain, a series of nerve cells responsible for strength and movement of the muscles. This may cause stiffness and pain of the muscles and if untreated leads to complications of the bones and joints.

White Matter: The central part of the brain that is made up of myelin and glial cells.