About SMA

Spinal Muscular Atrophy (SMA) is a motor neuron disease. The motor neurons affect the voluntary muscles that are used for activities such as crawling, walking, head and neck control, and swallowing.

It is a relatively common “rare disorder”: approximately 1 in 6000 babies born are affected, and about 1 in 40 people are genetic carriers.

SMA affects muscles throughout the body, although the proximal muscles (those closest to the trunk of one’s body – i.e. shoulders, hips, and back) are often most severely affected. Weakness in the legs is generally greater than in the arms. Sometimes feeding and swallowing can be affected. Involvement of respiratory muscles (muscles involved in breathing and coughing) can lead to an increased tendency for pneumonia and other lung problems.

Sensation and the ability to feel are not affected. Intellectual activity is normal and it is often observed that patients with SMA are unusually bright and sociable.

Patients are generally grouped into one of four categories, based on certain key motor function milestones (Types 1, 2, 3 & 4) Type 1 is the most severe form of the disease, type 4 the least severe.

SMA is a genetic disease where both parents are carriers. 2 carrier parents have a 25% chance of parenting a child with SMA. They would have a 50% chance of parenting a child that is a carrier of SMA. They would have a 25% chance of parenting a child that is not a carrier and also does not have the disease.

See also Understanding SMA (pdf) Print copies of this booklet are available by contacting our office.



Spinal Muscular Atrophy Type 1

Werdnig-Hoffman Disease

The diagnoses of type 1 SMA is usually made when the child is between 3 – 6 months of age.  This is the most severe form of SMA.   Some mothers even notice a decreased movement in the final months of her pregnancy. A child with type 1 is typically never able to lift his/her head or accomplish the normal gross and fine motor skills expected early on in infancy.  They generally have poor head control, and may not kick their legs as vigorously as they should.  They typically never bear weight on their legs or sit unsupported.  Swallowing and feeding may be difficult and are usually affected at some point, and the child may show some difficulties managing their own secretions.   Tremors can be seen on the tongue.  There is weakness of the intercostal muscles (the muscles between the ribs) that help expand the chest when breathing.  The chest is often smaller than usual, giving the trunk a bell shape.  The child with SMA type 1 generally uses the diaphragm to breath, giving them the appearance to breathe with their stomach.  Due to this type of breathing, the lungs never fully develop, the child has a weak cough.   They may have a difficult time taking a deep breath while sleeping, affecting their ability to maintain normal oxygen and carbon dioxide levels.

Caring for a type 1 child

While most children diagnosed with Type I are still infants there are a myriad of things that can be done to assist in the cognitive, physical and emotional health of your child. Using balloons and feathers as toys makes for wonderful stimulation and allows them a feeling of independence and accomplishment. Reaching games are a form of physical or occupational therapy that can be very helpful. Instructions in range of motion and other physical/occupational therapy ideas by a licensed therapist are important no matter how young the child. Your physical/occupational therapist can also suggest ideal seating systems that will be most helpful in the comfort and maximum mobility of your child.

Water therapy can be very helpful as the buoyancy of the water allows movement of the arms and legs that may otherwise not be there. Be sure that the water temperature is at least 90˚F and that the child’s head does not go under the water or into the water. You must watch so that the child has no possibility of aspirating (getting fluid into their lungs).

Children with SMA who have difficulty swallowing are at risk for aspirating when eating. Sometimes the child may aspirate his/her own secretions. The child may choke while eating and may also experience weight loss as swallowing becomes more difficult. Assistive feeding may be necessary. Two possible options are:

Nasogatric Tube (NG-Tube): a surgically placed tube through the nose that goes directly into the stomach. Gastrostomy Tube (G-Tube): a surgically placed tube through the skin that goes directly into the stomach. Because a child with SMA Type I has difficulty coughing, contacting a respiratory therapist is very important so you can be instructed in chest physiotherapy (CPT). CPT is a method of clearing the lungs of accumulated mucus by using positioning and clapping on the chest to assist in loosening secretions. Saliva can settle in the nasopharynx causing a faint gurgling sound. Often the secretions or mucus need to be removed by the use of a suction machine. Blowing raspberries and bubbles encourages respiratory strength.

Individuals with SMA can also benefit from the use of a cough assist machine. The CoughAssist™ achieves this by applying a positive pressure to the airways to inflate the lungs, and then rapidly shifts to negative pressure to pull the air out of the lungs. The rapid shift in pressure produces a high expiratory flow from the lungs, simulating a cough. This technique, referred to as “mechanical insufflation-exsufflation,” avoids airway damage while clearing the lungs of secretions. The device offers patients greater comfort and quality of life without the use of invasive procedures and equipment. Patients as young as 4 months have been able to use the CoughAssist™ successfully.

Respiratory distress can be monitored by measuring the level of oxygen saturation in the blood using a tool called a pulse oximeter. A small clip or tape with a red light and a sensor is placed on the patient’s finger or toe to determine the oxygen saturation. Children with SMA Type I usually require breathing support while sleeping. Some children require more breathing support, especially with colds. There are several options to consider.

BiPAP (Bilevel Positive Airway Pressure) uses a nasal mask with a cap, which fits over the head to hold it in place over the nose. BiPAP provides a higher volume of air into the lungs during inhalation and inflates the lung greater than what the person can do on their own. During exhalation, the BiPAP pressure drops so that air can passively leave the lungs. The BiPAP machine can sense when the person is taking a breath and give the breath in synchrony with the individual. A respiratory rate is also set so that the BiPAP gives a minimum number of breaths per minute. The person can breathe above that rate and the BiPAP will deliver more breaths. CPAP (continuous positive air pressure) should never be used in patients with SMA.

Negative Pressure Ventilation refers to providing breaths into the lungs using a large chamber or tank that encircles the chest similar to the old Iron Lung. The chamber is connected to a vacuum pump that takes the air out of the chamber and, as a result, the chest wall expands to bring air into the lungs. A Port-A-Lung is an example of a negative pressure ventilator. It can be set to deliver a specific number of breaths per minute and a vacuum pressure.

Mechanical ventilators or respirators come in a variety of models. Mechanical ventilators are more complex, but also allow for control of more variables. The ventilator can be set to deliver a specific size breath at a set number of breaths per minute. Mechanical ventilation can be delivered with a nose mask, mouthpiece while awake, or through a tracheostomy tube. A tracheotomy is placement of a surgical hole in the neck to the large airway (trachea) that a tube can be inserted. A tracheostomy tube bypasses the mouth and vocal cords and goes directly from the skin to the trachea (wind-pipe). A respirator or ventilator is connected to the endotracheal tube or tracheostomy tube. Consult your physicians and respiratory therapists or contact Families of SMA Canada for literature.

It is important to understand your rights when it comes to making life-sustaining decisions for your child. Be sure that both parents discuss their feelings about this very delicate topic. It is a decision that cannot be made lightly and all options should be covered. Talking to a counselor in the department of social services at your hospital may be helpful. Once your decision has been reached be sure that you put it in writing, and that all necessary medical personal and family members are aware of your wishes. This is your decision, one you have reached with great care and anguish, and under no circumstances should you allow others to judge you or place their values upon you. You are never alone. Families of SMA Canada is always just a phone call or email away.


Researchers have identified the SMN1 gene as the primary manufacturer of the SMN Protein. It is the absence/defect of this SMN1 gene that causes Spinal Muscular Atrophy. However, there is another form of this gene called SMN2. The SMN2 gene is similar to SMN1, but does not produce as much protein, or the right kind of protein, as the SMN1 gene. One determination of prognosis is the number of copies of the SMN2 gene. The greater the number of SMN2 copies, the more SMN protein is produced and the greater likelihood that more motor neurons remain healthy and productive. Individuals with only 1 or 2 copies of the SMN2 gene will typically have the most severe expressions of SMA. Three or more copies of the SMN2 gene will typically mean a less severe expression.

Each type of SMA has variability among individual patients. Please keep this in mind when considering an individual’s care.

Raising a child with SMA should be no different than raising a child who is not affected. Do as many things as possible that are age appropriate. Many times this means making adaptations. It is very important that children with SMA are assisted in reaching their utmost potential.

It is important to understand that parents and patients have rights and that you are not alone. Most hospitals have social service departments that can give you a shoulder to lean on. Don’t be afraid to say NO if something doesn’t seem right. Don’t be intimidated or afraid to ask questions. If you forget to ask something, call your doctor or contact Families of SMA for suggestions. In this context, it is also important that your child be followed by a physician who is familiar with SMA and its complications.

Spinal Muscular Atrophy Type 2

Diagnosis of Type II SMA is almost always made before 2 years of age, with the majority of cases diagnosed by 15 months. Children with this type may sit unsupported when placed in a seated position, although they are often unable to come to a sitting position without assistance. At some point they may be able to stand. This is accomplished with the aid of assistance or bracing and/or a parapodium/standing frame.

Swallowing problems are not usually characteristic of Type II, but vary from child to child. Some patients may have difficulty eating enough food by mouth to maintain their weight and grow, and a feeding tube may become necessary. Children with Type II SMA frequently have tongue fasciculation and manifest a fine tremor in the outstretched fingers.

Children with Type II also have weak intercostals muscles and are diaphragmatic breathers. They have difficulty coughing and may have difficulty taking deep enough breaths while they sleep to maintain normal oxygen levels and carbon dioxide levels.

Scoliosis is almost uniformly present as these children grow, resulting in need for spinal surgery or bracing at some point in their clinical course. Decreased bone density can result in an increased susceptibility to fractures.  Major causes for concern include the Respiratory System, as once weakened it never fully recovers.

Spinal Muscular Atrophy Type 3

The diagnosis of Type III, often referred to as Kugelberg-Welander or Juvenile Spinal Muscular Atrophy, is much more variable in age of onset, and children can present from around a year of age or even as late as adolescence, although diagnosis prior to age 3 years is typical.

The patient with Type III can stand alone and walk, but may show difficulty with walking at some point in their clinical course. Early motor milestones are often normal. However, once they begin walking, they may fall more frequently, have difficulty in getting up from sitting on the floor or a bent over position, and may be unable to run.

With Type III, a fine tremor can be seen in the outstretched fingers but tongue fasciculations are seldom seen. Feeding or swallowing difficulties in childhood are very uncommon.

Type III individuals can sometimes lose the ability to walk later in childhood, adolescence, or even adulthood, often in association with growth spurts or illness.

Spinal Muscular Atrophy Type 4

Adult Onset SMA

In the adult form, symptoms typically begin after age 35. It is rare for Spinal Muscular Atrophy to begin between the ages of 18 and 30. Adult onset SMA is much less common than the other forms. It is defined as onset of weakness after 18 years of age, and most cases reported as type IV have occurred after age 35. It is typically characterized by insidious onset and very slow progression. The bulbar muscles, those muscles used for swallowing and respiratory function, are rarely affected in Type IV.

Patients with SMA typically lose function over time. Loss of function can occur rapidly in the context of a growth spurt or illness, or much more gradually. The explanation for this loss is unclear based on recent research. It has been observed that patients with SMA may often be very stable in terms of their functional abilities for prolonged periods of time, often years, although the almost universal tendency is for continued loss of function as they age.



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