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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.

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.


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.

Amniotic fluid

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


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.


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.


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.


Lack of coordination

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

Definition from: by Merriam-Webster Inc.


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.


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

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)


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


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


Abnormal enlargement of the heart.

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.



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.

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.

Cephalic vein

Cephalic vein

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.

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. 
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.


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.

Coarsening of the facial features

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

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.


The study of human chromosomes.

Deoxyribonucleic Acid (DNA)

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


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

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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.

DNA analysis

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

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.


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:

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.


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.

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.


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

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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.


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

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.


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.


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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