Spinal muscular atrophy (SMA) is a complex disease — a glossary of terms can be a helpful resource for understanding some aspects of the disease
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.
KAFO: A Knee Ankle Foot Orthosis is a lower extremity orthotic used to
control instabilities in the knee and lower limb.
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 muscular atrophy (SMA) Type I SMA or infantile-onset SMA (also known as Werdnig-Hoffmann
disease):1
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”. Type II SMA or intermediate SMA (also known as Dubowitz disease):
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. Type III SMA or juvenile-onset SMA (also known as Kugelberg-Welander
disease):
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. Type IV SMA or adult-onset 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.
