• Atrophy (of skeletal muscle): A reduction in the size of muscle fibres, the strength of the muscle, and resistance to fatigue.

  • Autosomal recessive disorder: In an autosomal recessive disorder such as spinal muscular atrophy, 2 copies of an abnormal gene must be present in order for the disease or trait to develop. In other words, both parents must be carriers of the trait.

  • Bilevel positive airway pressure (BiPAP): A BiPAP machine provides 2 levels of positive airway pressure delivered via a mask (nasal/mouth). The machine delivers a higher pressure and increased volume when the patient inhales. On exhalation, the machine lowers the pressure to allow for a more normal breathing pattern.

  • Carrier: A carrier is an individual who carries and is capable of passing on a genetic mutation associated with a disease, though they may or may not display symptoms. Two carriers may produce a child with the disease.

  • Central nervous system (CNS): The CNS is the part of the nervous system that includes the brain and spinal cord.

  • Chromosome: A chromosome is an organised package of genetic material called DNA, which is found in the nucleus of a cell. The nucleus is the command centre of the cell, giving instructions to the cell to grow, mature, divide, or die. DNA, or deoxyribonucleic acid, is the genetic material found in humans and almost all other living organisms.

  • Cognition: The mental action or process of acquiring knowledge and understanding through thought, experience, and the senses.

  • Cough assist device: A machine that helps to clear secretions from the lungs. On inhale, air is pushed into the lungs to help them expand. On exhale, the machine creates a sucking force that pulls air out of the lungs and helps make the cough stronger and more effective.

  • Electromyography (EMG): A diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons).

  • Hypoventilation: Hypoventilation occurs when breathing is too shallow or slow and the lungs are not inhaling enough oxygen or exhaling enough carbon dioxide. When it occurs during sleep, it is one of the earliest signs of breathing difficulties in individuals with SMA.

  • Motor neurons: Motor neurons are nerve cells in the spinal cord that send the signals that cause muscles to contract.

  • Nasogastric (NG) tube: An NG tube is a narrow tube passed into the stomach through the nose. It is used for short- or medium-term nutritional support.

  • Noninvasive (NIV) respiratory care: This term usually refers to respiratory support (including bilevel positive airway pressure, or BiPAP, ventilation) that does not require endotracheal intubation (breathing tube) or tracheostomy (trach tube). The short-term goals of NIV include relief of respiratory distress, reduced work of breathing, improved oxygenation, and making the patient more comfortable. Ultimately, the purpose is to help support the patient’s respiratory function while avoiding the need for tracheotomy.

  • Nonsitters: A term used to describe children with spinal muscular atrophy who are not able to sit independently.

  • Palliative care: The type of patient care that aims to improve the quality of life for patients with a life-threatening illness. Palliative care is intended to relieve pain and other symptoms that can cause the patient distress and discomfort. This approach does not mean that the patient is near death. According to the World Health Organization, palliative care in children is best accomplished by a multidisciplinary care team that includes the family.

  • Percutaneous endoscopic gastrostomy tube (PEG tube): A PEG tube delivers liquid feedings directly to the stomach via a tube inserted through the abdomen. It is inserted during a brief surgical procedure and allows people with feeding problems to maintain proper nutrition and fluids.

  • Proximal muscles: The proximal muscles are those closest to the centre of the body.

  • Referral: An order or permission granted by the primary care provider to receive specialty care.

  • Scoliosis: A deviation in the normally straight vertical line of the spine—causing the spine to take on an S-shaped curve.

  • Sitters: A term that describes those children with spinal muscular atrophy who can sit without assistance but cannot walk independently.

  • Spinal

    Spinal muscular atrophy (SMA)

    Infantile-onset SMA (also known as Werdnig-Hoffmann disease or Type I SMA): Infantile-onset is the most severe form of SMA, comprising 60% of all cases of the disease. It is often diagnosed during an infant’s first 6 months of life. Affected individuals are unable to sit and are also referred to as “nonsitters”.

    Intermediate SMA (also known as Dubowitz disease or Type II SMA): Intermediate SMA is usually diagnosed between 7 and 18 months. Affected individuals can typically sit up (also known as “sitters”) without help, though they may need assistance getting into a seated position. However, they are typically unable to walk and may require a wheelchair.

    Juvenile-onset SMA (also known as Kugelberg-Welander disease or Type III SMA): Juvenile-onset SMA is usually diagnosed after 18 months of age, but before the child is aged 3 years. Individuals affected by Type III SMA are initially able to walk (also known as “walkers”), but may lose mobility as they grow, and may eventually need to use a wheelchair.

    Adult-onset SMA (also known as Type IV SMA): This type of SMA is very rare. Mild motor impairment is seen in adulthood. Symptoms can begin as early as age 18, though they often begin after age 35.

  • Survival motor neuron 1 (SMN1) gene: The SMN1 gene produces a protein called survival motor neuron protein (SMN protein), which is important for the maintenance of specialised nerve cells called motor neurons. Without SMN protein, motor neurons die, and nerve impulses are not passed between the brain and muscles. As a result, some muscles cannot perform their normal functions, leading to weakness and impaired movement.

  • Survival motor neuron 2 (SMN2) gene: Also called the SMA "back-up gene". Several different versions of the SMN protein are produced from the SMN2 gene, but only one version is full size and functional.

  • Ventilation (mechanical ventilation): A mechanical ventilator is a machine that helps people breathe when they’re unable to breathe sufficiently on their own. Mechanical ventilation can be noninvasive, using nose/mouth masks, or invasive, involving endotracheal intubation.