Glossary

A

Adult stem cells

Adult or somatic stem cells exist throughout the body after embryonic development and are found inside of different types of tissue. These stem cells have been found in tissues such as the brain, bone marrow, blood, blood vessels, skeletal muscles, skin and the liver. They remain in a state of dormancy or non-dividing state for years until activated by disease or tissue injury.

Allele

These are a particular form of gene. Alleles occur in pairs, one on each chromosome inherited from each parent. Your doctor may refer to the mutation present on each allele (copy) of your child’s disease causing gene.

Amino acids

Organic molecules that link together to form proteins.

Analgesic medication

A medication that reduces the symptom of pain.

Anticipatory grief

Carers often feel grief even though the person they’re caring for is still alive, but has a life-limiting condition.

Although not everyone experiences this ‘anticipatory grief’, people who do can feel the same emotions and sense of mourning as if the person has actually died.

Aspiration

The entrance of foreign materials into the lungs. Such materials can include food, saliva or nasal secretions.

Ataxia

A specific form of imbalance and impaired coordination that results from neurological disease. Individuals with Tay-Sachs or Sandhoff have a progressive form of ataxia which becomes more obvious as the disease develops. They lose muscle coordination, have gait problems (more prominent in the Juvenile and LOTS forms of Tay-Sachs) and lose the ability to function independently.

Autosomal recessive

When both copies of the gene need to be mutated in order to cause disease.

Autosome

An autosome is a non-sex-related chromosome. We all have 23 pairs of chromosomes and the term “autosomal” refers to the chromosome pairs 1 to 22.

B

Beta-hexosaminidase A (HEX A)

This is an enzyme that is encoded by the HEXA gene. Beta-hexosaminidase A and the cofactor GM2 activator protein catalyze the breakdown of the ganglioside GM2.

Beta-hexosaminidase B (HEX-B)

This is an enzyme that is encoded by the HEXB gene. Beta-hexosaminidase B and the cofactor GM2 activator protein catalyze the breakdown of the ganglioside GM2.

Blood brain barrier

A highly selective barrier formed by blood vessels and special brain cells called astrocytes that allow molecules to cross from blood to brain.

C

Carrier

Sometimes called a “genetic carrier,” is an individual who has one mutated copy of a gene. The other copy of that gene on the other partner chromosome is not affected by that mutation. Carriers do not develop Tay-Sachs or Sandhoff disease as two mutated copies of the gene are required to develop the disorder.

Catabolism

The breakdown of complex (large) materials such as proteins or lipids within an organism into simpler forms. This results in the release of energy.

Catalysis

An increase in the rate of (a speeding up of) a chemical reaction.

Cells

The basic unit for life, bound by a protective membrane. Cells contain the information which allows them to replicate and function within the body.

Central Nervous System

Your central nervous system (CNS) is made up of your brain and your spinal cord.

Your brain controls most of the functions of your body, including awareness, movement, what you think and say, and what you see, hear, feel, taste and smell.

Your spinal cord is an extension of your brain. It carries messages to and from your brain via the network of nerves connected to it.

Cerebellum

Part of the brain located at the back, which is responsible for the coordination of movement.

Cerebrum

Main part of the brain which is responsible for motor and sensory functions, speech, vision and hearing.

Cherry-red spot

Most individuals with infantile Tay-Sachs and Sandhoff disease have a cherry red macula in the retina (also known as a cherry red spot), observable by a physician when examining the eye. This is commonly the first sign that the individual may be affected by a GM2 gangliosidosis.

This red spot is blood vessels in a retinal area that show through as red next to the pale gangliosides that have accumulated in the surrounding retinal nerve cells.

Chromosome

Chromosomes are packages of DNA. They are located in the nucleus (centre) of each cell. We each have 23 pairs of chromosomes with one chromosome from each pair inherited from our mother and one from our father – 22 autosome pairs and 1 sex chromosome pair.

Constipation

A gastrointestinal problem resulting in hard and/or dry faeces (poo) that is difficult to pass.

Counsellor

A person you can talk to so they can help you overcome difficulties in your life. Some counsellors specialise in certain areas such as finances or grief, and many are trained Clinical Psychologists.

Cytosol

The internal liquid content of a cell that contains many of the simple and complex molecules required for the cell to function.

D

Dietitian

Dietitians help people to understand the relationship between food and health.

DNA (deoxyribonucleic acid)

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. The information in DNA is stored as a code. Within the cell DNA is packaged as chromosomes.

Dysarthria

A motor speech disorder resulting from neurological damage and characterized by poor articulation.

Dysphagia

People with dysphagia have difficulty swallowing and may even experience pain while swallowing. Some people may be completely unable to swallow or may have trouble safely swallowing liquids, foods or saliva. When that happens, eating becomes a challenge, and often dysphagia makes it difficult to take in enough calories and fluids to nourish the body. This can lead to additional serious medical problems for an individual.

Dystonia

A specific form of hypertonia that differs from, but is similar to, spasticity.

E

Embryonic stem cells

These cells are derived from a four- or five-day-old human embryo that is in the blastocyst phase of development. The embryos are usually extras that have been created in IVF (in vitro fertilization) clinics where several eggs are fertilized in a test tube, but only one is implanted into a woman.

Enzyme

An enzyme is a protein that acts as an activator or catalyst, and it increases the rate of a chemical reaction within the cell.

Enzyme replacement therapy

Enzyme replacement therapy, or ERT, involves replacing a missing enzyme in individuals who are deficient or lack a particular enzyme. This approach is used to treat some lysosomal disorders, however this is not effective in Tay-Sachs or Sandhoff disease.

Equipment providers

Commonly non-government companies that specialise in the supply of equipment, modifications and other types of supports for people living with disability.

G

Ganglioside

A ganglioside is a special type of sphingolipid, that is found especially in brain cells. The brain needs gangliosides to function.

Genes

Genes are one of the basic units of life. They contain the recipes for who you are. Genes are coded within our DNA sequence which is packaged into larger packets called chromosomes.

Gene editing

An emerging therapeutic technology which enables correction of a genetic mistake within a living cell. You might hear this referred to as “CRISPR”. Scientists are attempting to develop gene editing as a therapy for Tay-Sachs and Sandhoff disease, however such approaches are not currently available treatments.

Gene therapy

Involves the replacement of a defective gene with a normal working copy of the gene to restore cell function and correct disease. Scientists are attempting to develop gene editing as a therapy for Tay-Sachs and Sandhoff disease, however such approaches are not currently available treatments.

General Practitioner (GP)

GPs (family doctors) are doctors who have completed training in general practice. They have a broad knowledge and the skills to treat a range of health issues.

Genetic counsellor

Genetic counsellors help people make informed decisions about genetic testing, interpret test results and communicate the implications of the results for the individual and their family members.
Genetic counsellors also consider the implications of a genetic diagnosis on the patient’s immediate and extended family.

Genome

The total complement of genes on all the chromosome pairs that define a person’s life cycle.

Genotype

The genetic make-up of each individual person which is completely unique to themselves.

Glycolipids

A group of complex molecules which have both a lipid and carbohydrate component.

Glycosphongolipids

A type of glycolipid that contains a sphingolipid with one or more carbohydrate attached to them.

GM2 Ganglioside Activator (GM2A)

This is a protein which in humans is encoded by the GM2A gene. The protein encoded by this gene is a small transport protein which supports function of the lysosomal enzyme β-hexosaminidase Ato degrade GM2 ganglioside.

GM2 Ganglioside (or ‘GM2’)

A type of ganglioside. G refers to ganglioside and the M is for monosialic (as it has one sialic acid), and 2 refers to the fact that it was the second monosialic ganglioside discovered.

GM2 gangliosidoses

A group of related genetic disorders, including Tay-Sachs and Sandhoff diseases, that result from a deficiency of the enzyme/s that break down GM2 gangliosides.

H

Heterozygous

This is a condition that exists if the corresponding genes on each of the related pair of chromosomes are different to each other. The different genes can be normal or disease causing.

Hexosaminidase

A group of specialized lysosomal enzymes responsible for the breakdown of GM2 Ganglioside. In Tay-Sachs and Sandhoff diseases the abnormal enzyme is called β-hexosaminidase. (‘β’ is pronounced ‘beta’)

β-hexosaminidase is made up of two individual parts (called subunits). These subunits are named the α and β subunits and are coded for by the HEXA and HEXB genes respectively. (‘α’ is pronounced ‘alpha’)

Gene mutations in the HEXA gene are the main cause of Tay-Sachs disease and mutations in the HEXB gene cause Sandhoff disease.

Homozygous

This is a condition that exists if the corresponding genes on each of the related pair of chromosomes are the same. The genes may both be normal or disease causing.

Hydrotherapy

Hydrotherapy involves the use of water for pain relief and treatment.

Hypertonia

Hypertonia is a state of increased muscle tone (the amount of tension or resistance to movement in a muscle)

Hypotonia (low muscle tone)

A state of low muscle tone (the amount of tension or resistance to movement in a muscle).

I

Infantile Tay-Sachs / Sandhoff

The earliest presenting form of the diseases. The signs of infantile disease usually appear after a child’s first six months of life, prior to which they have appeared to be developing normally.

J

Juvenile Tay-Sachs / Sandhoff

The juvenile forms of the diseases are rarer than the infantile forms and are usually initially seen in children between the ages of 2 – 10 years.

L

Late onset Tay-Sachs / Sandhoff (LOTS)

Adult onset, also known as Late Onset Tay-Sachs disease (LOTS), is a very rare form of Tay-Sachs and Sandhoff disease that usually occurs in individuals in their 20s and early 30s, although may present later in life.

Lipid

An organic molecule that is insoluble in water, for example fatty acids. Lipids are critical components of cells and important for their normal function. However, in excess they can cause disease. A ganglioside is a special type of lipid.

Lysosomal Storage Disorders (LSD)

A group of more than eighty inherited genetic, metabolic disorders that result from defects in lysosomal function. Tay-Sachs and Sandhoff diseases are lysosomal disorders.

Lysosomes

A lysosome is a dynamic cellular compartment that contains digestive enzymes that break down and recycle excess or worn-out cell parts.

M

Macrocephaly

The term used to describe the state of having an increased head size.

Metabolic pathway

Refers to a linked series of chemical reactions (metabolic processes) that take place within cells.

Metabolic specialist

A metabolic specialist is a specialist doctor who diagnoses and treats disorders of metabolism.

Metabolism

Refers to all the chemical processes the body uses to produce energy.

Mutation

A change, or variation, on a gene that makes it faulty. The result of the mutation is that the gene does not perform the function that it should.

N

Nasogastric tube (NG)

A medical process involving the insertion of a plastic tube (nasogastric tube or NG tube) through the nose, past the throat, and down into the stomach. It is used for feeding and administering drugs and other oral agents.

National Disability Insurance Scheme (NDIS)

The NDIS is a federally funded support scheme which provides eligible Australians with disability funding for connections to services and equipment.

Importantly, the NDIS is separate from your state health system.

NDIS, Local Area Coordinator (LAC)

LACs are representatives of the NDIS who help people understand and access the NDIS. They also work with NDIS participants to develop and use their NDIS plan.

Neurodegenerative

Progressive functional loss due to the nervous system as a result of disease.

Neurologist

A specialist doctor who diagnoses and treats conditions of the brain, spinal cord and nerves.

Neurology

A branch of medicine concerned especially with the structure, function, and diseases of the nervous system, including the brain and spinal cord.

Neuron

A nerve cell.

Neuropathology

Changes that occur within the brain as a result of disease.

Nucleus

A specialised compartment within the cell which contains its chromosomes.

Nurse

A professional clinician who provides holistic care and liaises with all members of the multidisciplinary team to achieve the best possible patient outcomes.

O

Occupational Therapist (OT)

Occupational therapy is used when someone is having difficulty with everyday tasks. OT’s help to find suitable, practical solutions.

Organelle

A functional sub-unit of the cell which has a special role in cell function. The lysosomes are an example of an organelle.

P

Palliative care team

Palliative care is person and family-centred care for someone with an active, progressive, advanced disease, who has little or no prospect of cure and who is expected to die, and for whom the primary goal is to optimise the quality of life.

Palliative care helps people live their life as fully and as comfortably as possible. It identifies and treats symptoms which may be physical, emotional, spiritual or social.

Most palliative care teams are known as multidisciplinary, which means that they have a mix of doctors, nurses and various other types of health professionals. The team works together, and alongside other specialist and community teams.

Percutaneous Endoscopic Gastrostomy (PEG)

Also known as gastrostomy or simply PEG tube feeding. To enable PEG tube feeding, a surgical procedure is performed under anaesthesia, to insert a small, flexible feeding tube through the abdominal wall and into the stomach.

PEG tube feeding allows nutrition, fluids and medications to enter the stomach directly. In avoiding the mouth and oesophagus, it also avoids any difficulties in chewing or swallowing and any aspiration risk.

Pharmacist

Can dispense medicines and provide advice regarding safe use of medicines.

Physiotherapist

Focused on helping people when they have a problem with movement to assist them to become more comfortable.

Plasma membrane

Also known as the cell membrane, this is the outer boundary of the cell. Lipids are important components of the cell membrane.

PRN medication

Medications that are taken ‘as required’ are known as ‘PRN’ medications.

Proteins

Large organic molecules that perform many of the metabolic activities taking place with a cell. Typical roles are as enzymes, transporters, receptors, sensors, activators and structural elements. The proteins are constructed from chains of smaller components called amino acids, linked together in a sequence defined by the DNA.

Psychologist

Experts in human behavior. They have studied how the mind works and how people think, react and behave. Psychologists may also specialise in an area such as grief counselling.

R

Recessive

The effects of a genetic mutation that are only evident when both copies of a gene pair are abnormal.

Reflux

When weakened muscles allow acid to leak up into the oesophagus.

S

Secretions

Commonly refers to saliva, but can also refer to those originating in the nose, throat or lungs.

Sedation

The inducing of a relaxed easy state, especially by the use of sedative agents.

Seizure

Seizures (also known as fits or convulsions) are caused by rapid and uncoordinated electrical firing in the brain. This can cause alternating stiffening and jerking of the arms and legs, and a loss of consciousness or altered consciousness level.

Sex chromosomes

Sex chromosomes, or sex-related chromosomes, are the non-autosomal chromosomes (X and Y) inherited from parents. They are the 23^rd pair of chromosomes. Females have two copies of the X chromosome, while males have an X and a Y chromosome.

Social worker

Help people to face life’s challenges, improve their wellbeing, and do their best to ensure they are treated fairly.

Spasticity

A specific form of hypertonia.

Speech Pathologist

Aims to help people who aren’t able to communicate effectively or with problems with speech, language, communication, fluency, voice, swallowing food or drinking safely.

Sphingolipids

A special type of lipid that is critical for cell function. . Sphingolipids are abundant in the central nervous system and it is their breakdown and recycling which is faulty in Tay-Sachs and Sandhoff disease. Gangliosides are a type of sphingolipid found within the brain.

Stem cells

A class of undifferentiated cells that are able to differentiate into specialized cell types. Commonly, stem cells come from two main sources; embryos formed during the blastocyst phase of embryological development (embryonic stem cells), and adult tissue (adult stem cells). Both types are generally characterized by their potency, or potential to differentiate into different cell types (such as skin, muscle or bone).

Substrate

A substrate is a substance that is acted upon, for example by an enzyme. In Tay-Sachs and Sandhoff diseases the term substrate is used to define the large lipid molecules that cannot be effectively broken down by the faulty enzyme.