Glossary Amino Acid Amino acids are the basic building blocks of proteins. The type and order of amino acids which join together to make a protein are determined by DNA in the cell that produces the protein, and will affect the structure and function of the protein in the body. Ataxia Telangiectasia (AT) Ataxia Telangiectasia (AT) is a rare childhood neurological disorder. Affected children show impaired coordination and balance (ataxia) and may also have a weakened immune system, frequently suffering from infections. A high number of affected children also develop cancers such as leukaemia or lymphoma. Telangiectasia’s are small, red veins which may appear on the surface of the ears and cheeks or in the corners of the eyes in patients. There is currently no cure. More information on AT can be found on the A-T society homepage. Cerebellar Ataxia Cerebellar ataxia is a form of ataxia that originates in the cerebellum. Symptoms include the inability to coordinate balance and eye movements among other symptoms. DNA / RNA DNA and RNA are made up of nucleic acids. They are important in the process of transcription and translation, which is necessary for making proteins from DNA. A DNA strand is made up of repeating units called nucleotides, linked to a backbone made of sugar and phosphate. The four different nucleotides are: adenine, cytosine, guanine and thymine, and are often represented by their first letters: A, C, G and T. RNA is a molecule similar to DNA and made from the DNA template during protein synthesis. (See Transcription and Translation for more information about protein synthesis.) Enzyme Enzymes are biological molecules that catalyse (i.e. increase the rates of) chemical reactions. Many medicines are enzyme inhibitors, decreasing the activity of enzymes and slowing or preventing chemical reactions in the body. Exon / Intron An exon is the portion of a gene that codes for amino acids. In the cells of plants and animals, most gene sequences are broken up by one or more DNA sequences called introns. Because they are expressed during transcription and translation (see below), exons code for proteins whilst introns are not expressed thus do not code for a protein. Friedreich’s ataxia Friedreich's ataxia results from the degeneration of nerve tissue in the spinal cord, in particular sensory neurons essential (through connections with the cerebellum) for directing muscle movement of the arms and legs. It manifests in initial symptoms of poor coordination such as gait disturbance; it can also lead to scoliosis, heart disease and diabetes. Friedreich’s ataxia is related to a reduction of the protein frataxin, due a mutation in the frataxin gene. Gene Therapy This therapeutic strategy aims to correct problems in the body caused by genetic mutations, for example by inserting healthy genes into the body where it is needed. There is a lot of research in this area, and it is currently being looked at as a potential therapy for some ataxias. Heterochromatin A tightly packed form of DNA. It may control the expression of certain genes through regulation of transcription initiation (see transcription below). Histone Deacetylase inhibitors During the transcription of genes, DNA is coiled and uncoiled around a histone backbone, with the help of molecules called histone acetylases, which add acetyl groups to make an open, active structure which can be read. Histone deacetylases (HDAC) remove these acetyl groups, making the chromatin structure dense and unreadable. HDAC inhibitors are a class of compounds that interfere with the removal of acetyl groups from the DNA structure, thus making it open and readable again. HDAC inhibitors have a history of use in psychiatry and neurology as mood stabilisers and anti-epileptics. More recently, HDAC inhibitors are being studied as a potential therapy for neurodegenerative diseases invluding ataxias. Hypertrophic cardiomyopathy Hypertrophic cardiomyopathy is a heart condition associated with Friedreich’s ataxia. The heart muscle becomes thickened and can obstruct the flow of blood. The severity and symptoms vary according to individuals. Some people need no treatment whilst others require medication, surgery or other treatments. Idiopathic Idiopathic means ‘of unknown cause’, which translates in medical terms as a disease with an unknown or uncertain origin. Inheritance (Dominant & Recessive) Each gene in the human body contains one allele from each parent. Sometimes, one allele can dominate over the other, meaning it either prevents or lessens the effect of the recessive allele. Certain types of ataxia can be classed as being passed down the family by dominant or recessive inheritance. Dominant inheritance means that to inherit ataxia, you have to inherit a dominant allele for the disease, whilst recessive inheritance means that you have to inherit two recessive alleles to develop the disease. MRI scan MRI (Magnetic resonance imaging) scans are used in medical imaging to give clear pictures of structures inside the body, such as the brain and spine. It uses magnets instead of radiation as used in other scanning methods such as CT scanning. MRS MRS (Magnetic resonance spectroscopy) is another type of imaging used in medicine, which gives information about the dynamics of a structure, such as changes in temperature, activity and metabolism. It is used to study the brain disorders, and the metabolic conditions of muscles and nerves. Mitochondria Mitochondria are organelles in each cell which use oxygen and nutrients to create energy. They are sometime called the ‘powerhouses’ or ‘batteries’ of cells and are found in varying numbers in all cells, depending on the energy requirements of the cell. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as cell growth and cell death. Mitochondria have been implicated in several human diseases and may play a role in the aging process. Oxidative stress/Oxidation Oxidation is a chemical reaction that produces free radicals, which start chain reactions that damage cells in a process called oxidative stress. As free radicals are molecules with an unpaired electron, they usually like to exist in pairs. Until they pair, free radicals can be very volatile and unstable, causing damage to cells in the process. Specifically, oxidative stress is caused by an imbalance between the production of toxic free radicals and the body’s ability to detoxify or easily repair the resulting damage. This is why oxidative stress is linked to various diseases, including the ataxias. Antioxidants slow or prevent oxidative damage to cells by reacting with the damaging free radicals, terminating these chain reactions. Examples of antioxidants include Vitamin A,C and E. Phenotype A phenotype is the qualities of an organism which can be seen such as appearance (e.g. blue eyes, brown hair…etc) or behaviour, as opposed to its genotype - the inherited instructions in its DNA. Placebo An inactive pill, liquid or other substance with no medical value that is used in clinical trials as a control to compare against an experimental treatment. This is used to rule out the placebo effect from the results. The placebo effect describes the improvement in a person’s condition due to the psychological expectations of taking a medication, even if the medication holds no medical value. Sensory nerve Sensory nerves receive information from parts of the body, such as how something feels and if it is painful. They are made up of nerve fibers which relay this information to the central nervous system (the spinal cord and the brain). Spinocerebellar degeneration Spinocerebellar degeneration and cerebellar degeneration describe changes that have taken place in a person’s nervous system. Cerebellar and spinocerebellar degeneration have many different causes. Stem cells / Differentiation Stem cells are unspecialised cells that have not yet differentiated into any specific type, but have the potential to. They are unique because they can reproduce themselves infinitely. They can also generate more specialised cell types, such as muscle, nerve or bone cells. Stem cells are found in various places in the body, for example bone marrow, blood and the umbilical cord. Cellular differentiation is the process by which a less specialised cell from a fertilised egg becomes a more specialised cell type such as a nerve cell or muscle cell. Differentiation also occurs in adults during tissue repair and normal cell turnover. Transcription / Translation Transcription is the production of RNA following the instructions contained in DNA. Both DNA and RNA sequences use the same language, and the information is simply transcribed, or copied, from one molecule to the other. DNA sequence is copied to produce a complementary nucleotide RNA strand, called messenger RNA (mRNA), which carries the genetic message from the DNA to the protein-synthesizing machinery of the cell. The end product of transcription is a protein, which makes up many functions in the body, such as enzymes or muscle tissue. Proteins are made from amino acids, which are transcribed from a trinucleotide (or codon), a set of three nucleotides which carry the genetic code to make an amino acid. During the process of translation, a ribosome decodes the mRNA to produce a specific amino acid chain or polypeptide. The polypeptide later folds into an active protein and performs its functions in the cell. This process is a part of gene expression.