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Tay-Sachs, Canavan, Sandhoff, GM1 and related diseases


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Term Definition

An enzyme that breaks down a particular type of fatty substances, Fabry disease is characterized by its absence.

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Adeno-Associated Virus (AAV)

A member of the parvovirus family, which is composed of small viruses with a genome of a single-stranded DNA. AAVs insert genomic material at a specific site on human chromosome 19 with nearly 100% certainty, and are used to construct vectors that introduce genes into cultured cells. There is virtually no downside to AAV vectors, given the small amount of DNA they can carry and because AAV is non-pathogenic (most people are AAV carriers). In contrast to adenoviruses, AAV usually does not trigger an immune response to cells infected with it, and thus can deliver genes to sites of interest, including the brain in the context of gene therapy for diseases of muscle and eye, tissues where AAV seems to be most useful.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

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A procedure used for prenatal diagnosis, which involves insertion of a needle through the abdomen into the amniotic fluid. This procedure is performed using ultrasound guidance, and allows the physician to obtain a small amount of amniotic fluid which can then be used for testing. Amniocentesis is usually performed between 16 and 18 weeks of pregnancy, but some centers offer "early amnio" at 14 weeks of pregnancy.

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Amniotic fluid

Amniotic fluid is the nursing and protecting contained by the amniotic sac. It is used for genetic screening of the fetus.

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Angiokeratomas are small dark red to purple raised spots. They may also have a rough scaly surface. They are composed of surface blood vessels (dilated capillaries). Often unnoticed, they may become crusty and bleed if accidentally scratched or damaged, or a harmless clot may form in the lesion (thrombosis), changing the color to dark purple or black overnight.

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An enzyme that breaks down a N-acetylaspartate acid into parts thought to be necessary for proper myelin production and maintenance, Canavan disease is characterized by its absence.

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The inhalation of either food or stomach contents into the lower airways. This can lead to aspiration pneumonia and aspiration pneumonitis. Although these two diagnoses are managed differently, they are often interchangeably referred to as aspiration pneumonia.

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Lack of coordination

An inability to coordinate voluntary muscular movements that is symptomatic of some nervous disorders.

Definition from: by Merriam-Webster Inc.

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Wasting away or diminution. Muscle atrophy is wasting of muscle, decrease in muscle mass.

A nerve can also show atrophy. For example, atrophy of the optic nerve diminishes vision.

Definition from: by MedicineNet Inc.

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Refers to genes that are not found on the sex chromosomes. Those chromosomes that are not XX and XY, i.e. sex-linked.

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Autosomal recessive

Describes a trait or disorder requiring the presence of two copies of a gene mutation at a particular locus in order to express observable phenotype; specifically refers to genes on one of the 22 pairs of autosomes (non-sex chromosomes)

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 A measurable substance in an organism whose presence is indicative of some phenomenon such as disease, infection, or environmental exposure.


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Blood-brain barrier (BBB)

A network of blood vessels with closely spaced cells that makes it difficult for potentially toxic substances (such as anticancer drugs) to penetrate the blood vessel walls and enter the brain. (Definition from: Unified Medical Language System)

A naturally occurring barrier created by the modification of brain capillaries (as by reduction in fenestration and formation of tight cell-to-cell contacts) that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues -- abbreviation BBB. (Definition from: Merriam-Webster's Medical Dictionary

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Abnormal enlargement of the heart.

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Carotid artery

Arteries carry oxygen-rich blood away from the heart to the head and body. There are two carotid arteries (one on each side of the neck) that supply blood to the brain. The carotid arteries can be felt on each side of the lower neck, immediately below the angle of the jaw.

The carotid arteries supply blood to the large, front part of the brain, where thinking, speech, personality and sensory and motor functions reside.



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Carrier testing

Carrier testing can determine if a person carries one of the altered genes that cause a recessive disease. DNA carrier testing establishes the presences or absences of particular mutation(s). Enzymatic testing evaluates the level of activity of an enzyme, which when absent causes disease. In some diseases the enzyme test is not sensitive enough to determine carrier status.

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Central nervous system

The central nervous system is that part of the nervous system that consists of the brain and spinal cord. The central nervous system (CNS) is one of the two major divisions of the nervous system. The other is the peripheral nervous system (PNS) which is outside the brain and spinal cord. The peripheral nervous system (PNS) connects the central nervous system (CNS) to sensory organs (such as the eye and ear), other organs of the body, muscles, blood vessels and glands. The peripheral nerves include cranial nerves, spinal nerves and roots, and what are called the autonomic nerves that are concerned specifically with the regulation of the heart muscle, the muscles in blood vessel walls, and glands.

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Cephalic vein

Cephalic vein

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Cerebrospinal fluid (CSF)

The fluid within the subarachnoid space, the central canal of the spinal cord, and the four ventricles of the brain. The fluid is formed continuously by the choroid plexus in the ventricles, and is reabsorbed into the blood by the arachnoid villi at approximately the same rate at which it is produced.

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Cherry-red spot
The term ‘cherry red spot’ describes the appearance of the retina when viewed by an eye specialist that is associated with metabolic neurological disorders like Tay-Sachs, Sandhoff, GM-1, Niemann-Pick, MPS and other similar disorders.
Warren Tay described the cherry red spot in Symmetrical changes in the region of the yellow spot in each eye of an infant, published in Transactions of Ophthalmology Society UK in 1881:
…in the region of the yellow spot in each eye there was a conspicuous, tolerably defined, large white patch, more or less circular in outline, and showing at its centre a brownish-red, fairly circular spot, contrasting strongly wit the white patch surrounding it.
Disappearance of the cherry-red spot is not indictiative of disease lessening.
Endoplasmic reticulum and Enzyme definitions are swapped. 
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Chorionic Villus Sampling (CVS)

A procedure used for prenatal diagnosis, which involves insertion of a needle through the abdomen into fingerlike projections of the placenta which are called chorionic villi. This procedure is also performed using ultrasound guidance, and testing can be performed with the tissue obtained. Depending upon the location of the placenta, the tissue may be obtained transvaginally rather than abdominally, by inserting a catheter through the cervix and into the uterus. CVS is usually performed at 10 to 12 weeks of pregnancy.

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Structures found in the nucleus of the cell, which are visible under a microscope and which contain genetic (inherited) information. Human cells contain 46 chromosomes, which come in pairs. There are twenty-two pairs of chromosomes which are referred to as autosomes, because they do not determine the sex of an individual. The twenty-third pair are referred to as the sex chromosomes, and are called the X and Y chromosomes. Each chromosome contains thousands of individual genes, which will in turn determine an individual's characteristics.

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Coarsening of the facial features

Short noses, flat faces and large head is often described as coarsening of facial features

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Community screenings

Organized carrier testing outreach events to educate high risk ethic groups on the importance of genetic screening and to provide convenient free or reduced cost testing.

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The study of human chromosomes.

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Deoxyribonucleic Acid (DNA)

The chemical sequence found in genes, and which allows for the transmission of inherited information from generation to generation.

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Points away from the center of the body. Distal muscles are in the limbs, opposite of proximal

For more details visit

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Distended abdomen

Alternate names: Swollen belly; Swelling in the abdomen; Abdominal distention.

Distended abdomen may be cause by variety of reasons, in the allied disease it is typically caused by, the enlargement of the liver and spleen, also called hepatosplenomegaly.

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DNA analysis

DNA analysis looks for particular or known mutations in the genome or genetic make up.

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Dominant Inheritance

A pattern of inheritance whereby a single gene mutation may lead to a specific genetic disease. Children of an individual affected with a dominantly inherited condition (often referred to as autosomal dominant if the gene is not located on the X or Y chromosomes) have a 50% chance to inherit the gene mutation.

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Speech that is characteristically slurred, slow, and difficult to produce (difficult to understand). The person with dysarthria may also have problems controlling the pitch, loudness, rhythm, and voice qualities of their speech. Definition from:

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Endoplasmic reticulum (ER)

A substance that in small amounts increases the rate of a specific biochemical reaction. Often enzymes are required for the normal metabolism, or breakdown, of substances in the body.

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A complex pipe-like system of membranes that occupies much of the cytoplasm in cells and which contains many of the enzymes which are responsible for the breakdown of metabolic waste into reuse able parts.

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Enzyme assay

Measurement of enzyme activity with particular substrate, for example an enzyme assay for Tay-Sachs disease measures the Hex A activity with GM2 gangliosides.

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Muscle twitches are fine or tiny uncontrollable movements of a small area of muscles. Some are common while others are associated with neurological disease.

For more details visit:

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Any of a group of glycolipids that yield a hexose sugar on hydrolysis and are found especially in the plasma membrane of cells of the gray matter.

Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.

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Often referred to as the "unit of heredity". A gene is composed of a sequence of DNA required to produce a functional protein.

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Genetic counseling

As defined by the National Society of Genetic Counselors, is the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease. This process integrates:

-Interpretation of family and medical histories to assess the chance of disease occurrence or recurrence.

-Education about inheritance, testing, management, prevention, resources and research.

-Counseling to promote informed choices and adaptation to the risk or condition.

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The glucocerebrodidase enzyme is necessary for the breakdown of a particular fatty substance, glucocerebroside into glucose and ceramide. Gaucher disease is characterized by its absence.

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A type of fat (lipid) molecule accumulates in individuals with Gaucher disease and is used as a building block to make certain cell membranes. When the cells wear out, the glucocerebroside can be recycled. This recyclable material comes mainly from the breakdown of old red and white blood cells. In the brain, glucocerebroside comes from the processing of lipids during brain development and the formation of the myelin sheath (the fatty coating around each nerve fiber).

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Simple sugar; the form in which all carbohydrates are used as the body's principal energy source; transported in the blood and metabolized in the tissues.

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Form in which foods are stored in the body as energy.

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Glycogen storage disorders

A class of disorders characterized by the build-up of glycogen causes progressive muscle weakness throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver, and nervous system.

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GM2 Ganglioside

A fatty substance or lipid that is part of normal metabolism, in Tay-Sachs and Sandhoff lack of enzyme function causes the GM2 gangliosides to accumulate which is toxic and eventually causes cell death.

Tay-Sachs and Sandhoff are known collectively as GM2.

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Hexosaminidase A

Tay-Sachs is caused by a mutation in the HEXA gene on chromosome 15. The HEXA gene codes for the alpha subunit of the hexosaminidase A enzyme which is necessary for breaking down GM2 gangliosides in nerve cells. When there is a mutation in the coding for alpha subunit of the hexosaminidase A it does not function properly and leads to an accumulation of GM2 which is toxic and eventually causes cell death. Sandhoff is characterized by loss of function of both the alpha and beta subunit of hexosaminidase A enzyme. For more information visit:

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Hexosaminidase B

Sandhoff is caused by a mutation in the HEXB gene on chromosome 5. The HEXB gene codes for part of two essential nervous system enzymes: the beta subunit of hexosaminidase A and the beta subunit of hexosaminidase B. When there is a mutation in the coding for beta subunit of hexosaminidase A and the beta subunit of hexosaminidase B both enzymes do not function properly and lead to an accumulation of GM2 which is toxic and eventually causes cell death. Tay-Sachs is characterized by loss of function of only the alpha subunit of the hexosaminidase A enzyme. For more information:

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Decreased muscle tone, limpness.

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in·tra·vas·cu·lar (intrəˈvaskyələr/)
adjective: intravascular
  1. situated or occurring within a vessel or vessels of an animal or plant, especially within a blood vessel or blood vascular system.
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Joint stiffness

Allied diseases often interfere with muscle control and subsequent joint movement leading to stiffness and reduced range of motion.

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Lentivirus (lentiviral)

Lentivirus represents a genus of slow viruses with long incubation period (months, even years) and a propensity to induce a wide range of pathologies in different animal species. Due to their rather flexible genome and a potential of transducing many forms of nondividing cells, lentiviruses have become one of the most widely used vectors for gene transfer. (

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A group of rare genetic disorders that affect the central nervous system by disrupting the growth or maintenance of the myelin sheath that insulates nerve cells. Myelin is commonly referred to as the brain's "white matter", myelin covers nerve cells and ensures the clear transmission of nerve impulses from one part of the body to another. These disorders are progressive, meaning that they tend to get worse throughout the life of the patient.

The word leukodystrophy comes from the Greek words leuko (meaning white), trophy (meaning growth), and dys (meaning ill). If you put these words together, the word leukodystrophy describes a set of diseases that affect the growth or maintenance of the white matter (myelin).

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Linkage analysis

Linkage is the tendency for genes and other genetic markers to be inherited together because of their location near one another on the same chromosomes. Linkage analysis uses the location relationship to determine carrier status of particular genes.

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Large and complicated reddish-brown glandular organ located in the upper right portion of the abdominal cavity; secretes bile and functions in metabolism of protein and carbohydrate and fat; synthesizes substances involved in the clotting of the blood; synthesizes vitamin A; detoxifies poisonous substances and breaks down worn-out red blood cells. Definitions from: WordNet®

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Lorenzo's Oil

Is a combination of two fats extracted from olive oil and rapeseed oil and is specific to adrenoleukodystrophy (ALD), does not repair myelin, and does not have any known effect on other demyelinating disorders. In ALD presymptomatic boys Lorenzo's Oil often (but not always) prevents the onset of the disease by stopping the body from producing the very long chain fatty acids, whose buildup leads to demyelination. For more information visit the Myelin Project.

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Lysosomal storage disease

Lysosomal storage disease is a group of disorders that affect specific enzymes. These enzymes normally break down items for reuse in the cells. If the enzymes are missing or don't work properly the items can build up and become toxic.

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Organelle structures found within the cytoplasm of cells which contain digestive enzymes; responsible for breaking down the cell of debris into reusable parts.

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Depression in bipolar disorder is a mood disorder characterized by mood swings from mania (exaggerated feeling of well-being, energy, and confidence in which a person can lose touch with reality) to depression with the current or most recent episode of illness characterized by depression. For more details visit:

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mass spectrometry (ms/ms)

An instrumental method for identifying the chemical constitution of a substance by means of the separation of gaseous ions according to their differing mass and charge —called also mass spectroscopy.


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Metabolomics is a newly emerging field of "omics" research concerned with the comprehensive characterization of the small molecule metabolites in biological systems. It can provide an overview of the metabolic status and global biochemical events associated with a cellular or biological system. (

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Missense point mutation

Missense mutation (illustration)

This type of mutation is a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene.

(reposted from


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Mouse model

A laboratory mouse useful for medical research because it has specific characteristics that resemble a human disease or disorder. Strains of mice having natural mutations similar to human ones may serve as models of such conditions. Scientists can also create mouse models by transferring new genes into mice or by inactivating certain existing genes in them. Definition from: National Human Genome Research Institute (

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A change in the sequence of DNA. Many mutations are "silent" and do not cause disease. When mutations occur in genes and disrupt the production of a functional protein, they may lead to genetic disease.

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Is the white matter coating our nerves, enabling them to conduct impulses between the brain and other parts of the body. It consists of a layer of proteins packed between two layers of lipids. Myelin is produced by specialized cells: oligodendrocytes in the central nervous system, and Schwann cells in the peripheral nervous system. Myelin sheaths wrap themselves around axons, the threadlike extensions of neurons that make up nerve fibers. Each oligodendrocyte can myelinate several axons.

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N-acetyl-a-acid (NAA)

Aspartoacylase breaks down NAA into aspartic acid (an amino acid used in making proteins) and acetic acid. The cycle of production and breakdown of NAA appears to be critical for maintaining the brain's white matter, which consists of nerve fibers covered by myelin. NAA is likely essential for making certain fats (lipids) that are used to produce myelin.

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Neuronal stem cells

A stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells. Examples of glial cells include astrocytes and oligodenrocytes. Definition: National Institute of Health (

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Nerve cells, the structural and functional unit of the nervous system. A neuron consists of a cell body and its processes- an axon and one or more dendrites. Neurons function by starting and conducting impulses. Neurons transmit impulses to other neurons or cells by releasing neurotransmitters at synapses. Definition: National Institute of Health (

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Off-Label use is when physicians treat their patients using treatments approved for other uses but not officially approved for use for their particular disorder.

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A supporting cell that provides insulation to nerve cells by forming a myelin sheath (a fatty layer) around axons. Definition: National Institute of Health (

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Occurs in all ethnic groups.

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Pharmacological Chaperone Technology

Pharmacological chaperone technology involves the use of small molecules that selectively bind to and stabilize proteins in cells, leading to improved protein folding and trafficking, and increased activity.

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Pre-implantation Genetic Diagnosis (PGD)

Tests early-stage embryos produced through in vitro fertilization (IVF) for the presence of a variety of genetic conditions. One cell is extracted from the embryo in its eight-cell stage and analyzed. Embryos free of conditions that would cause serious disease can be implanted in a woman's uterus with the hopes of resulting in a healthy pregnancy.

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Prenatal Screening

Refers to a variety of tests to determine the health of the fetus. In some cases of known carrier couples of genetic disease prenatal analysis can show if the fetus is affected by the disease. See Amniocentesis and Chorionic villus sampling (CVS).

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A large complex molecule made up of one or more chains of amino acids. Proteins perform a wide variety of activities in the cell.

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Points near the center of the body. Proximal muscles are the trunk muscles and help maintain balance, opposite of distal. For more details visit:

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Psychosis is a loss of contact with reality, typically including delusions (false ideas about what is taking place or who one is) and hallucinations (seeing or hearing things which aren't there). For more details visit:

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Pyrimethamine is a drug is approved for treating malaria, and has also been found to have an effect on other diseases such as toxoplasmosis, a life-threatening parasitic infection. It has also been used as an off-label therapy for Tay-Sachs (Late Onset and Juvenile). Pyrimethamine is based on pharmacological chaperone technology.

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Recessive Inheritance

Pattern of inheritance whereby disease results only when an individual inherits two gene mutations for the particular disease. The parents of a child who is affected are said to be "carriers" of the disease, because they have one mutation and do not manifest symptoms. If both members of a couple are carriers, there is a 1 in 4 or 25% chance in each pregnancy for a child to be affected. Also referred to as autosomal recessive inheritance if the gene is not located on the X or Y chromosomes.

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A seizure is a sudden change in behavior due to an excessive electrical activity in the brain. There are a wide variety of possible symptoms of seizures, depending on what parts of the brain are affected. Many types of seizures cause loss of consciousness with twitching or shaking of the body. However, some seizures consist of staring spells that can easily go unnoticed. Occasionally, seizures can cause temporary abnormal sensations or visual disturbances.

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Sialidosis is a severe inherited disorder that affects many organs and tissues, including the nervous system. This disorder is divided into two types, which are distinguished by the age at which symptoms appear and the severity of features.

Mutations in the NEU1 gene cause sialidosis. This gene provides instructions for making an enzyme called neuraminidase 1 (NEU1), which is found in lysosomes. Lysosomes are compartments within the cell that use enzymes to digest and recycle materials. The NEU1 enzyme helps break down large sugar molecules attached to certain proteins by removing a substance known as sialic acid.

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Spasticity is a condition in which certain muscles are continuously contracted. This contraction causes stiffness or tightness of the muscles and may interfere with movement, speech, and manner of walking. Spasticity is usually caused by damage to the portion of the brain or spinal cord that controls voluntary movement. Symptoms may include hypertonicity (increased muscle tone), clonus (a series of rapid muscle contractions), exaggerated deep tendon reflexes, muscle spasms, scissoring (involuntary crossing of the legs), and fixed joints. The degree of spasticity varies from mild muscle stiffness to severe, painful, and uncontrollable muscle spasms. Spasticity can interfere with rehabilitation in patients with certain disorders, and often interferes with daily activities.

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A lipid or fat that is critical for the normal structure and function of cells and tissues. It is normally degraded into ceraminde by sphingomyelinase. Niemann-Pick Types A and B are characterized by the absences of the enzyme and the accumulation of sphingomyelin.

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An enzyme that resides within the lysosomes and is responsible for the conversion of a lipid (fat) called sphingomyelin into another type of lipid called ceramide. This lipid conversion is critical for the normal structure and function of cells and tissues. Niemann-Pick Type A and B are characterized by its absence and resultant accumulation of sphingomyelin.

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A large dark-red oval organ on the left side of the body between the stomach and the diaphragm; produces cells involved in immune responses Definitions from: WordNet®

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Startle response

The startle response or reflex is a normal reflex for an infant when he or she is startled or feels like they are falling. The infant will have a "startled" look and the arms will fling out sideways with the palms up and the thumbs flexed. Presence of the startle response in babies older than a few months is abnormal and associated with neurological damage. For more details visit:

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The substance on which an enzyme acts.

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Refers to genes that are found on the sex chromosomes: XX and XY. Fabry and PMD are x-linked allied diseases.

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