Glossary of Terms

ACTH Adrenocorticotropic Hormone:

Adrenocorticotropic hormone is produced by the pituitary gland. Its key function is to stimulate the production and release of cortisol from the cortex of the adrenal gland.Primary adrenal insufficiency, also called Addison’s disease, occurs when adrenal gland production of cortisol is chronically deficient, resulting in chronically elevated ACTH levels. A deficiency of ACTH is a cause of secondary adrenal insufficiency. Primary adrenal insufficiency is found in 85% of young boys who develop the most severe form of ALD.

Adrenal Glands:

These sit one top of each kidney and produce (secrete) three (3) types of hormones:

  • Glucocorticoid hormones produce cortisol which help maintain sugar (glucose) control, decrease immune response and helps the body to respond to stress
  • Mineralocorticoid hormones regulate such things as sodium and potassium
  • Sex hormones androgens (male) and estrogens (female)



An Allele is one or two of several forms of a gene found on a chromosome in a particular place, usually arising through mutation that are responsible for hereditary variation.

Allogenic Transplant:

Allogenic means that the transplanted cells are coming from a donor – this may be a sibling, other relative, or someone unrelated to the patient (the cells can even come from umbilical cord blood).


A sample of fluid (amniotic) is taken from the sac surrounding the baby by use of a needle. It is done 15-19 weeks from gestation. This contains foetal tissue and the DNA is tested for the known mutation, VLCFA’S and other tests that look at chromosome make up, size etc (Karyotyping)


The loss of the sense of smell, either total or partial


Any disease of the arteries.

ARSA Arylsulfatase A:

Arylsulfatase A or (cerebroside-sulfatase) is an enzyme that breaks down sulfatides, namely cerebroside 3-sulfate into cerebroside and sulfate. In humans, arylsulfatase A is encoded by the ARSA gene.

ASPA Asparatoacylase:

The ASPA gene provides instructions for making an enzyme called aspartoacylase. In the brain, this enzyme breaks down a compound called N-acetyl-L-aspartic acid (NAA) into aspartic acid (an amino acid that is a building block of many proteins) and another molecule called acetic acid. More than 80 mutations in the ASPA gene are known to cause Canavan disease. Studies suggest that if NAA is not broken down properly, the resulting chemical imbalance interferes with the formation of the myelin sheath as the nervous system develops.


A star shaped type of glial cell that is thought to provide physical and nutritional support for neurons. They are a very complex and their functions are not fully understood.


Ataxia is a lack of muscle coordination which may affect speech, eye movements, the ability to swallow, walking, picking up objects and other voluntary movements. A person with persistent ataxia may have damage in the part of the brain that controls muscle coordination – the cerebellum.


The wasting away or decrease in size of an organ or tissue in the body. When a body part is affected by an inability to function, the muscles may atrophy through lack of use and especially as a result of the degeneration of cells.

Autologous Transplant:

Autologous means structures or cells came from you and your body. In an autologous transplant the patient “donates” their cells to them self.


An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X and Y). Autosomes are numbered roughly in relation to their sizes. That is, Chromosome 1 has approximately 2,800 genes, while chromosome 22 has approximately 750 genes.

Autosomal Inheritance:

The gene responsible for the phenotype is located on one of the 22 pairs of autosomes (non-sex determining chromosomes).

Autosomal Dominant:

Dominant conditions that are manifest in heterozygotes (individuals with just one copy of the mutant allele).
Dominant conditions are expressed in individuals who have just one copy of the mutant allele. Affected males and females have an equal probability of passing on the trait to offspring. Affected individual’s have one normal copy of the gene and one mutant copy of the gene, thus each offspring has a 50% chance of inheriting the mutant allele. Approximately half of the children of affected parents inherit the condition and half do not.

Autosomal Recessive:

Recessive conditions are only manifest in individuals who have two copies of the mutant allele (are homozygous).
Recessive conditions are clinically manifest only when an individual has two copies of the mutant allele. When just one copy of the mutant allele is present, an individual is a carrier of the mutation, but does not develop the condition. Females and males are affected equally by traits transmitted by autosomal recessive inheritance. When two carriers mate, each child has a 25% chance of being homozygous wild-type (unaffected); a 25% chance of being homozygous mutant (affected); or a 50% chance of being heterozygous (unaffected carrier).


The axon is the long extension from the cell body – it can be as long as one metre- whose chief function is to send information to other neurons. The axons of most neurons in the nervous system are covered with a myelin sheath. This coating insulates the axon from electrical and chemical interference and dramatically increases the speed that a message is sent to the next neuron.

Bone Marrow Transplant BMT:

A BMT replaces bone marrow stem cells in people whose bone marrow has been destroyed by large doses of chemotherapy or radiotherapy. The healthy stem cells are put into your body intravenously, and then find their way into your bones to become healthy marrow. The transplant of healthy stem cells rescues you from your chemotherapy, and/or radiotherapy by enabling your bone marrow to start making new red and white blood cells and platelets.
They can be Allogenic or Autologous. Allogenic means that the transplanted cells are coming from a donor – this may be a sibling, other relative, or someone unrelated to the patient (the cells can even come from umbilical cord blood) or Autologous means structures or cells came from you and your body. In an autologous transplant the patient “donates” their cells to them self.


A cataract is a cloudiness or opacity in the normally transparent crystalline lens of the eye. This cloudiness can cause a decrease in vision and may lead to eventual blindness. Refsums and 4H are some that experience this problem.

Computed Axial Tomography (CAT Scans ):

Put very simply, a CAT scan is a very advanced X-Ray that is ideal for solid matter. Contrast agents will be given to a patient if the radiologist is looking for differences in like matter. They are rarely used for ALD these days as most hospitals have access to a MRI machine.

Central Nervous System (CNS):

The central nervous system consists of the brain and the spinal cord. The spinal cord carries out automatic motor responses, transmits sensory information to the brain and transmits messages from the brain to the muscles and organs. Each of the spinal cords segments controls sensation and movement in a different part of the body.

Cerebellar Ataxia:

This relates to the cerebellum which is that large structure at the back of the brain that receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements. The cerebellum coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity.
Cerebellar ataxia can occur as a result of lesions to the cerebellum and many diseases and presents with symptoms of an inability to coordinate balance, gait, extremity and eye movements.

Chorionic Villus Sampling (CVS):

A sample is taken from the lining of the uterus (Chorion) which becomes the placenta as these cells are mostly the same as the baby and both come from the same fertilised cell. It is done 11-13 weeks from gestation. It is usually done in a similar way to amniocentesis but it can be done as if you were having a Pap smear (done less often). This contains foetal tissue and the DNA is tested for the known mutation, VLCFA’S and other tests that look at chromosome make up, size etc (Karyotyping)


A chromosome is a long strand of DNA that contains many genes; there are 46 human chromosomes (22 pairs of chromosomes, and the X and Y chromosomes).
Women have 46 chromosomes (44 autosomes plus two copies of the X chromosome) 46,XX
Men have 46 chromosomes (44 autosomes plus an X and a Y chromosome) 46,XY

Craniofacial Dysmorphism:

Refers to an abnormality of the face and/or the head. Craniofacial dysmorphism can include abnormal growth patterns of the face or skull, and may involve the soft tissue as well as the bones. In the case of the Leukodystrophy 18q-syndrome, craniofacial abnormalities will most likely include deep-set eyes, a “carp-shaped” mouth, microcephaly (small head), prominent ears, and midfacial hypoplasia (underdeveloped midfacial regions).

DARS Gene:

The official name of this gene is “aspartyl-tRNA synthetase.” The DARS gene is located on the long (q) arm of chromosome 2. It has links to some Leukodystrophies when mutated.


The destruction, removal or loss of the myelin sheath on a nerve or nerves.


The dendrite is the arm that receives the neural information from other neurons (nerve cells) and passes it down to the axon.


The development and cutting of teeth.

Dominant Inheritance:

Dominant inheritance means an abnormal gene from one parent can cause disease, even though the matching gene from the other parent is normal. The abnormal gene dominates.


Inability to swallow


Inability to talk


A speech disorder caused by disturbances of muscular control because of damage to the central or peripheral nervous system. It relates to speech that is characteristically slurred, slow, and difficult to understand.


The improper laying down or breakdown of a myelin sheath of a nerve fibre caused by abnormal myelin metabolism.


A state of abnormal muscle tone resulting in muscular spasm and abnormal posture, typically due to neurological disease. Dystonia is a disorder characterized by involuntary muscle contractions that cause slow repetitive movements or abnormal postures. The movements may be painful, and some individuals with dystonia may have a tremor or other neurologic features.

Endocrine System:

The endocrine system is a collection of glands that secrete chemicals directly into the bloodstream. These chemicals are called hormones and some of those are: cortisol, aldosterone, adrenaline, noraadrenaline, testosterone, estrogen, oxytocin and dopamine. The main endocrine glands include: pituitary, pineal and hypothalamus, thyroid, pancreas, adrenal, testis and ovaries.


An enzyme is made from a group of complex proteins that are produced by living cells and act as catalysts in specific biochemical reactions. They speed up the chemical process. Not all enzymes are made from Amino therefore are not proteins. Enzymes are named by what they do.

Ependymal Cell:

Ependymal cells are glial cells that line the cavities of the brain that contain cerebrospinal fluid and the central canal of the spinal cord. Ependymal cells are involved in the production of cerebrospinal fluid.

Epiphyseal Dysplasia:

Epiphyseal dysplasia is a disorder of cartilage and bone development primarily affecting the ends of the long bones in the arms and legs (epiphyses). Symptoms, including joint pain that most commonly affects the hips and knees, early-onset arthritis, and a waddling walk. Although some people with epiphyseal dysplasia have mild short stature as adults, most are of normal height.

Recessive epiphyseal dysplasia is distinguished from the dominant type by malformations of the hands, feet, and knees and abnormal curvature of the spine (scoliosis). About 50 percent of individuals with recessive multiple epiphyseal dysplasia are born with at least one abnormal feature, including an inward- and upward-turning foot (clubfoot), an opening in the roof of the mouth (cleft palate), an unusual curving of the fingers or toes (clinodactyly), or ear swelling. An abnormality of the kneecap called a double-layered patella is also relatively common. Patients with Refsums disease often have shortened limbs.


An epicanthus or simply an eye fold are names for a skin fold of the upper eyelid covering the inner corner (medial canthus) of the eye.


Is the science that studies the patterns, causes, and effects of health and disease conditions in defined populations.


A 2 mm- 4 mm skin sample is taken from the child and it is grown to a culture. From this many tests can be done to look at the DNA, enzyme activity and other chemical assays.

Galactocerebrosidase GALC:

The GALC gene provides instructions for making an enzyme called galactosylceramidase. Through a process called hydrolysis, this enzyme uses water molecules to break down certain fats called galactolipids, which are found primarily in the brain and kidneys. Within cells, galactosylceramidase is found in enzyme-filled sacs called lysosomes where it hydrolyses specific galactolipids, including galactosylceramide and psychosine. Galactosylceramide is an important component of myelin, the protective covering around certain nerve cells that ensures the rapid transmission of nerve impulses. Psychosine forms during the production of myelin, and then it breaks down with help of galactosylceramidase. Under normal conditions, tissues contain very little psychosine. Mutations in this gene are associated with Krabbe disease, also known as globoid cell leukodystrophy.


A genotype is an individual’s collection of genes. The term also can refer to the two alleles inherited for a particular gene. The genotype is expressed when the information encoded in the genes DNA is used to make protein and RNA molecules. The expression of the genotype contributes to the individual’s observable traits, called the phenotype.

Genu recurvatum:

Genu recurvatum is a deformity in the knee joint, so that the knee bends backwards. In this deformity, excessive extension occurs in the knee joint. Genu recurvatum is also called knee hyperextension and back knee Experienced in Metachromatic Leukodystrophy (MLD) amongst other disorders.

Genital Hypoplasia:

Underdevelopment or incomplete development of the genitals. It is found in 18q ,POL111 leukodystrophy.


A common eye condition in which the fluid pressure inside the eye rises to a level higher than healthy for that eye. If untreated, it may damage the optic nerve, causing the loss of vision or even blindness. Experienced in MLD, Krabbe and other Leukodystrophies.

Glial Cell:

A supportive cell in the central nervous system. Unlike neurons, glial cells do not conduct electrical impulses. The glial cells surround neurons and provide support for and insulation between them. Glial cells are the most abundant cell types in the central nervous system. Types of glial cells include oligodendrocytes, astrocytes, ependymal cells, Schwann cells, microglia, and satellite cells.

Grey Matter:

The “grey matter” of the brain gets its colour from the cell bodies, dendrites and the unmyelinated axons.

Graft Versus Host Disease GVHD:

GVHD may occur after a bone marrow or stem cell transplant in which someone receives bone marrow tissue or cells from a donor. This type of transplant is called Allogenic. The newly transplanted cells regard the recipient’s body as foreign. When this happens, the newly transplanted cells attack the recipient’s body. GVHD does not occur when someone receives his or her own cells during a transplant. This type of transplant is called autologous.

Hematopoietic Stem Cell:

An immature cell that can develop into all types of blood cells, including white blood cells, red blood cells, and platelets. Hematopoietic stem cells are found in the peripheral blood and in the bone marrow. They are used in Bone Marrow Transplants (BMT) because the transplant of healthy stem cells can enable your bone marrow to start making new red and white blood cells and platelets.


Abnormal enlargement of the liver. Experienced in Zellwegers.


An individual who has two different forms of a particular gene (allele), one inherited from each parent.


An individual who inherits the identical forms of a particular gene (allele) from each parent.


The term hydrocephalus is derived from the Greek words “hydro” meaning water and “cephalus” meaning head. As the name implies, it is a condition in which the primary characteristic is excessive accumulation of fluid in the brain.
Although hydrocephalus was once known as “water on the brain,” the “water” is actually cerebrospinal fluid (CSF) — a clear fluid that surrounds the brain and spinal cord. The excessive accumulation of CSF results in an abnormal widening of spaces in the brain called ventricles. This widening creates potentially harmful pressure on the tissues of the brain.


Hyper means excessive, over, more than normal

Hyperextension of the Limbs:

The extension of the limbs beyond their normal movement


Hypo means inadequate, under, less than normal


Hypodontia is the most common developmental dental anomaly in humans and is characterized by one or more (but <6) missing teeth. Hypodontia can be non-syndromic (isolated) or syndromic (associated with a systemic condition or syndrome).


Hypogonadism occurs when the sex glands produce little or no sex hormones. The sex glands, which are also called the gonads, are the testes in men and the ovaries in women. Their reproductive functionality is also severely affected as well as experiencing normal puberty.

Hypogonadotropic Hypogonadism:

Hypogonadotropic hypogonadism is defined as low levels of the sex steroids estrogen and progesterone (hypogonadism) in patients who are hypogonadotropic (low) or have inappropriately normal levels of gonadotropins FSH and LH. The vast majority of cases of HH are diagnosed in men.


The defective formation of myelin in the spinal cord, brain or peripheral nervous system


Decreased response of the deep tendon reflexes, usually resulting from injury to the central nervous system or a metabolic disease.


Hypotonia is an abnormality of the skeletal muscle tone, which is indicative of genetic disorders or nervous system dysfunction. Patients with these tendencies display floppy limbs and an inability to sustain normal head position.


Icthyosis is a non contagious scaliness of the skin. These symptoms can range anywhere from scaliness of the palms and soles of the feet to scaliness on the trunk of the body. Some forms of ichthyosis are inherited while others are acquired in later life as a symptom of systemic disorders such as MLD.


An area of tissue that has undergone a type of cell death called necrosis, as a result of the shutting off the blood supply.


The term Leukodystrophy refers to a group of genetic disorders that are characterised by the imperfect growth, development or maintenance of the white matter which is known as myelin.The word leukodystrophy comes from the Greek word leuko meaning white and dystrophy which means impaired. It refers to impaired white matter.


Incidence is calculated as the number of new cases of a disease or disorder in a specified time, usually a year. It is calculated by the number of new cases of a disease or disorder in a specified time, usually a year, divided by the population that is being considered. In rare diseases it can be very small and is often shown as the number of people per 100,000. For example it is more easily understood as 6 per 100,000 rather than show it as 0.00006.


The term Leukoencephalopathy refers to any of a group of diseases or disorder that affects the white matter of the brain.

Loes Score:

Pronounced “less” named after its developer neuroradiologist Daniel J. Loes of the University of Minnesota
The Loes score was developed to measure the loss of myelin shown on a brain MRI. It operates on a continuous scale of 0-34 points. The higher the points the more myelin loss and it has a direct correlation to functionality.
Loes Score between 1 and 5 would denote normal cognitive functions with no neurological deficits.


The Lysosome is a specialist part of the cell (Organelle) and it contains a large range of digestive enzymes used primarily for digestion and removal of excess or worn-out organelles, food particles, and engulfed viruses or bacteria.

Magnetic Resonance Imaging (MRI):

This procedure does not involve radiation as do X-Rays and CAT Scans. It uses a very powerful magnetic field and radio waves to contrast the various soft tissues that we have in our bodies. This makes it ideal for looking at our brain. From the results the radiologists can see the difference in the white matter in our brain and where it is deficient and showing irregularities. We have enough established evidence and global experts that allows the medical field to interpret their findings. The MRI scan helps produce a result called the Loes Score which rates the severity of brain damage on a scale from 0 to 34. A score of 0.5 or thereabouts is normal; a score of 14 or more indicates severe ALD. This plays a large part in determining whether your child is a candidate for a BMT transplant for ALD.

Macroencaphaly/ Megalencephaly:

Megalencephaly is a condition that results in the development of an abnormally large brain. The weight of an average adult brain is between 1,300 and 1,400 grams (2.87 pounds and 3.09 pounds). A brain is megalencephalic if it weighs more than 1,600 grams (3.53 pounds). Those with Alexanders can experience it.


Microglia are the primary immune cells of the CNS. They act as the major inflammatory cell type in the brain, and respond to pathogens (disease carriers) and injury by becoming “activated” – a process whereby they rapidly change form, proliferate and migrate to the site of infection/injury where they eat and destroy pathogens as well as remove the damaged cells.


An unusual smallness of the jaws, especially the lower jaw.


Mitochondria are the power houses of the cell providing the body with over 90% of the energy it needs to sustain life. Mitochondria take in sugars and proteins from the food we eat and produce energy called adenosine triphosphate (ATP) that our bodies use to function properly. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA. When the mitochondria are not working properly, cells begin to die until eventually whole organ systems fail and the patient’s life itself is compromised. . Mitochondrial disease is a debilitating and potentially fatal disease that reduces the ability of the mitochondria to produce this energy.

Muscle flexion:

The act of bending a joint or limb in the body or the condition of being flexed or bent.


Myelin is the insulation material that is made from proteins and lipids (fats etc) that is produced in the neuron to coat and protect the transmission arm of the neuron – the axon. This process is called Myelination. Myelin is produced for the central nervous system in cells called an Oligodendrocytes and for the peripheral nervous system the same function is performed by the Schwann cells. The receiving arm of the neuron is called a dendrite and is not myelinated.
Myelin is a spongy substance which is white in appearance and those axons which are myelinated are referred to as “the white matter” of the brain.
The major purpose of the myelin is to increase the speed of transmission of an impulse (message) to the next neuron and also to prevent the electrical current from escaping. An impulse or message from one cell to another is an electro – chemical process. When this process is disrupted or destroyed by a dysfunctional metabolic process, with a genetic cause it can be classified as a Leukodystrophy.


Short sightedness. It plays a role in the pathology of 4H and POL111 N-acetyl-L-aspartate NAA:
N-acetyl-L-aspartic acid (NAA) is predominantly found in the neurons in the brain. The function of NAA is unclear. Researchers had suspected that it played a role in the production of the myelin sheath, but recent studies suggest that NAA does not have this function. The enzyme may instead be involved in the transport of water molecules out of neurons. It is involved in the pathology of Canavan Disease.


This term includes CAT Scans (Computerised Axial Tomography).MRI’s (Magnetic Resonance Imaging) MRI’s are mainly used these days because they are more precise.


A neuron is a nerve cell. There are three types of neurons: sensory, motor and interneurons. A neuron consists of a cell body, a non myelinated receiving arm called a dendrite and a myelinated sending arm called an axon. Neurons are the fundamental units of the nervous system. Life cannot function without them.


The NOTCH3 gene provides instructions for producing the Notch3 receptor protein. This receptor protein is located on the surface of the muscle cells that surround blood vessels (vascular smooth muscle cells). The Notch3 receptor protein is specific to arteries, which are blood vessels that carry blood from the heart to the rest of the body. The protein is not present in veins, which return blood to the heart. When certain molecules attach (bind) to Notch3 receptors, the receptors send signals to the nucleus of the cell. These signals then turn on (activate) particular genes within vascular smooth muscle cells. Notch3 receptors play a key role in the function and survival of vascular smooth muscle cells. These receptors are thought to be essential for the maintenance of healthy muscle cells in the brain’s arteries. Mutations in this gene cause CADASIL.


Rhythmic, oscillating motions of the eyes are called nystagmus. This to-and-fro motion is generally involuntary.


The major function of oligodendrocytes and the Schwann cells is the formation of myelin. Myelin acts as an insulator of axonal segments and is a prerequisite for the high velocity of nerve conduction, of up to 200 m/second. The Oligodendrocyte’s main function is to provide support and insulation to axons in the central nervous system whilst this function is performed by the Schwann cells in the peripheral nervous system. Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid and 20% protein.


A membrane-bound compartment or structure in a eukaryotic cell that performs a special function. A eukaryotic cell contains many organelles, for example, the nucleus, endoplasmic reticulum, golgi apparatus, mitochondria, and chloroplast.


Paraparesis (paraplegia) refers to partial (-paresis) or complete (-plegia) loss of voluntary motor function in the pelvic limbs.

Peripheral Nervous System (PNS):

The peripheral nervous system consists of neurons that carry messages to and from the central nervous system. The peripheral nervous system has subdivisions: the somatic and autonomic nervous systems. The somatic nervous system sends sensory information to the central nervous system and carries out its motor commands. The autonomic nervous system send information to and from the body’s internal structure that carry out basic life processes such as digestion and breathing.

Peripheral Neuropathy:

Peripheral neuropathy is a condition that develops as a result of damage to the peripheral nervous system — the vast communications network that transmits information between the central nervous system (the brain and spinal cord) and every other part of the body. Symptoms can range from numbness or tingling, to pricking sensations (paresthesia), or muscle weakness. Areas of the body may become abnormally sensitive leading to an exaggeratedly intense or distorted experience of touch (allodynia). In such cases, pain may occur in response to a stimulus that does not normally provoke pain. Some forms of neuropathy involve damage to only one nerve and are called Mononeuropathies. More frequently however, multiple nerves are affected, called Polyneuropathy.


Is another specialist part of a cell (organelle) containing catalase, peroxidase, and other oxidative enzymes (proteins) and performing essential metabolic functions, as the decomposition of fatty acids and hydrogen peroxide.


A phenotype is an individual’s observable traits, such as height, eye colour, and blood type. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype, while other traits are largely determined by environmental factors.


Prevalence is the number of living cases of a disease or disorder that exist at any point in time. In rare diseases it can be shown as the number of people per 100,000. For example it is more easily understood as 2 per 100.000 rather than show it as 0.00002.


Proteins are made from molecules that are that are polymers of Amino Acids. Not all proteins function as enzymes. Proteins are named by what they are made from.


Quadriplegia is paralysis caused by illness or injury to a human that results in the partial or total loss of use of all their limbs and torso; Paraplegia is similar but does not affect the arms. The loss is usually sensory and motor, which means both sensation and control are lost.

Recessive inheritance:

Recessive inheritance means both genes in a pair must be abnormal to cause disease. People with only one defective gene in the pair are called carriers. However, they can pass the abnormal gene to their children.

Retinitis Pigmentosa:

Retinitis pigmentosa (RP) refers to a group of inherited disorders that slowly lead to blindness due to abnormalities of the photoreceptors (primarily the rods) in the retina. It affects night vision and peripheral vision, and eventually can lead to blindness. It is experienced with Refsums Disease.

Rosenthal Fibres:

A Rosenthal Fibres is an oval or elongated abnormal eosinophilic mass seen present in the CNS that are characteristic of Alexander Disease

Schwann cells:

The major function of oligodendrocytes and the Schwann cells is the formation of myelin. Myelin acts as an insulator of axonal segments and is a prerequisite for the high velocity of nerve conduction, of up to 200 m/second. The Oligodendrocyte’s main function is to provide support and insulation to axons in the central nervous system whilst this function is performed by the Schwann cells in the peripheral nervous system. Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid and 20% protein.


Scoliosis is a sideways curvature of the spine. While scoliosis can be caused by conditions such as cerebral palsy, muscular dystrophy and leukodystrophy, the cause of most scoliosis is unknown. Most cases of scoliosis are mild, but some children develop spine deformities that continue to get more severe as they grow. Severe scoliosis can be disabling. An especially severe spinal curve can reduce the amount of space within the chest, making it difficult for the lungs to function properly. Children who have mild scoliosis are monitored closely, usually with X-rays, to see if the curve is getting worse. In many cases, no treatment is necessary. Some children will need to wear a brace to stop the curve from worsening. Others may need surgery to keep the scoliosis from worsening and to straighten severe cases of scoliosis.


A seizure is a sudden surge of electrical activity in the brain which will affect how a person appears or acts for a short time. It is uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms. The type of symptoms and seizures depend on where the abnormal electrical activity takes place in the brain, what its cause is, and such factors as the patient’s age and general state of health. Some seizures can hardly be noticed, while others are totally disabling. Please refer to this link as an invaluable resource:


A state of increased tone of a muscle (and an increase in the deep tendon reflexes). For example, with spasticity of the legs (spastic paraplegia) there is an increase in tone of the leg muscles so they feel tight and rigid and the knee jerk reflex is exaggerated Calibri White Matter:Myelinated axons give some parts of the brain a white appearance (hence the term “white matter”).

X-linked inheritance:

A mode of genetic inheritance where the gene responsible for the disease or disorder is located on the X chromosome.

X-linked Recessive:

X-linked recessive traits are not clinically manifest when there is a normal copy of the gene. All X-linked recessive traits are fully evident in males because they only have one copy of the X chromosome, thus do not have a normal copy of the gene to compensate for the mutant copy. For that same reason, women are rarely affected by X-linked recessive diseases, however they are affected when they have two copies of the mutant allele. Because the gene is on the X chromosome there is no father to son transmission, but there is father to daughter and mother to daughter and son transmission. If a man is affected with an X-linked recessive condition, all his daughter will inherit one copy of the mutant allele from him.

X-linked Dominant:

Because the gene is located on the X chromosome, there is no transmission from father to son, but there can be transmission from father to daughter (all daughters of an affected male will be affected since the father has only one X chromosome to transmit). Children of an affected woman have a 50% chance of inheriting the X chromosome with the mutant allele. X-linked dominant disorders are clinically manifest when only one copy of the mutant allele is present.