Spinal muscular atrophy (SMA) is a complex disease—a glossary of terms can be
a helpful resource for understanding some aspects of the disease


Appeal: If an insurance company denies your claim for coverage of care or equipment, such as physical therapy or a power chair, you have the right to request that they reconsider the decision with an appeal. This may require you to fill out paperwork and provide detailed documentation. For urgent cases, your insurance company may speed up its appeals process.

Atrophy (of skeletal muscle): A reduction in the size of muscle fibers, the strength of the muscle, and the 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 organized package of genetic material called DNA, which is found in the nucleus of a cell. The nucleus is the command center 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.

Coinsurance: A type of cost-sharing that requires an individual to pay a specified percentage of the cost of a particular healthcare service or product.

Copay: A type of cost-sharing that requires an individual to pay a fixed dollar amount for a particular healthcare service or product.

Cost-sharing: The share of costs covered by an individual’s insurance plan that must be paid for by the individual.

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.

Deductible: A type of cost-sharing that requires an individual to pay a specified amount out of pocket before coverage can begin.

Distal hereditary motor neuropathy or Type V SMA: This condition has a different genetic cause from SMA Types I-IV. Type V SMA is very rare and typically affects the hands and feet only, causing muscle weakness and wasting. Symptoms usually begin during adolescence, but may occur from infancy through the mid-thirties.

Durable medical equipment: Equipment and supplies ordered by a healthcare professional for everyday or extended use, such as a wheelchair or cough assist device.

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

Gastrostomy tube (G-tube): A G-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.

Government health insurance: A broad category of health insurance coverage, under which insurance benefits are provided through a government program, such as Medicare or Medicaid.

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.

In-network provider (or preferred provider): A provider who has been contracted by an insurer to provide healthcare services to its members.

Invasive ventilation: Invasive respiratory support usually describes the use of a mechanical ventilator, which is connected to the patient via an airway. This may require a tracheotomy and cuffed tracheostomy tube.

Medicaid: A health insurance program that is administered by the state government, along with the Children’s Health Insurance Program, to provide coverage for individuals with low incomes or for children with disabilities and special needs. In most states, Medicaid beneficiaries are typically covered by one of the following programs:

  • Fee-for-service state Medicaid, which is operated by the state government as a single statewide program
  • Medicaid Managed Care, which is operated by private health plans contracted by the state

Medical necessity: Healthcare services or supplies that meet the accepted standards of care and are needed in order to prevent, diagnose, or treat an illness, injury, condition, disease, or its symptoms.

Medicare: A government health insurance program that provides coverage for individuals older than 65 years and for those with certain disabilities.

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.

Nasojejunal (NJ) tube: A small tube that is passed through the nose and guided into the jejunum (small bowel). It is used to feed people who are not able to get enough nutrients by eating.

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: Children with spinal muscular atrophy who are not able to sit independently.

Out-of-network provider (or nonpreferred provider): A provider who does not have a contract with an insurer to provide healthcare services to its members.

Out-of-pocket costs: The amount of money an individual may have to pay for the cost of covered healthcare services that he or she receives, as defined by the cost-sharing structure under his or her insurance benefits.

Out-of-pocket limit: A cost-sharing limit that is set on the amount of money an individual must pay out of pocket before the insurer covers the full cost of healthcare services.

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.

Premium: The amount that must be paid by a family or an individual to obtain coverage. For some people with private commercial coverage, their employer may pay for at least a portion of the health insurance premium.

Primary insurance (or primary payer): For people with more than one source of health insurance, this is the main source of coverage that pays first, unless a particular healthcare service or product is not covered.

Private commercial insurance: A broad category of health insurance coverage, under which benefits are privately purchased through an employer, directly from a health plan, through a broker, or a public health insurance marketplace (also known as an insurance exchange). Individuals with private commercial insurance may have a range of benefits, including:

  • Health maintenance organization, where coverage is typically granted only if patients use in-network providers
  • Preferred provider organization, where patients may use out-of-network providers, but at a higher out-of-pocket cost

Provider network: A group of healthcare professionals (eg, physicians), facilities (eg, hospitals), and suppliers (eg, DME suppliers) that are contracted with an insurer to provide services and products to its members.

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

Public health insurance marketplace (or exchange): A public entity that facilitates the purchase of private commercial health insurance when employer-sponsored insurance is not available or is unaffordable. Individuals with limited income who obtain coverage through the public insurance marketplace may be eligible for government subsidies to help reduce premiums and/or cost-sharing.

Pulmonologist: Pulmonologists are internal medicine doctors with specific expertise and experience in the treatment of diseases of the lungs and the management of breathing disorders.

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.

Secondary/supplemental insurance (or secondary/supplemental buyer): For those with more than one source of health insurance, this is an additional source of coverage that pays for the services or costs not covered by the primary health insurance.

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

Spinal muscular atrophy (SMA)

Infant-onset SMA (also known as Werdnig-Hoffmann disease or Type I SMA): Infant-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.

Spinal muscular atrophy with respiratory distress (SMARD): A disease similar to Type 1 SMA caused by a genetic mutation in a different gene than SMN1. Infants with SMARD are in severe respiratory distress because they have extremely weak breathing muscles.

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 specialized 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.

Tracheotomy: A tracheotomy is a surgical procedure to create an opening through the neck into the trachea (windpipe). A tube (tracheostomy tube) is usually placed through the opening to provide a secure airway and enable the removal of secretions from the lungs.

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.