Spinal muscular atrophy facts for kids
Spinal muscular atrophy (SMA) is a serious genetic disease that causes nerves and muscles to stop working. Babies affected by SMA often get weak and might die after their lungs fail. Adults who develop the disease gradually lose the ability to move their bodies. The muscle weakness is known to worsen as the patient ages.
Spinal muscular atrophy is inherited from parents who might or might not have the disease themselves but both of whom have a fault (mutation) in their genes that predisposes to the disease. Around one in 25 to one in 50 persons, depending on the country, carries a faulty gene of SMA.
Spinal muscular atrophy is the most common genetic disease causing deaths of babies. Medications that target the genetic cause of the disease include nusinersen, risdiplam, and the gene therapy medication onasemnogene abeparvovec. Supportive care includes physical therapy, occupational therapy, respiratory support, nutritional support, orthopaedic interventions, and mobility support.
Contents
Types
Type 0
It can already be observed before birth. It is the most rare and most severe form of the condition. Infants who have it tend to move less in the womb. As a result, they are often born with joint deformities or contractures. They have very weak muscle tone (hypotonia) at birth. Their respiratory muscles are also very weak. Most of them do not survive past infancy due to respiratory failure. Some also develop congenital heart defects.
Type I
Also known as Werdnig-Hoffmann disease is the most common form of all. Its severe form can be seen at birth or within the first few months. Children affected cannot control their head movements. Others may struggle sitting down without any assistance. Others may have difficulty swallowing, which often lead to difficulty feeding. Some may also develop breathing problems because of the weakness of their respiratory muscles. Due to respiratory failure, most patients who suffer from this type of condition do not survive past early childhood.
Type II
It is also called Dubowitz disease. It is identified by muscle weakness that develops in children between ages 6 and 12 months. They usually cannot sit without support. Apart from difficulty sitting, they usually cannot stand nor walk without help. Other signs include involuntary trembling (tremors) in their fingers, develop scoliosis, and respiratory muscle weakness that can be life-threatening. Many individuals with this type of condition often can only live up to their twenties or thirties.
Type III
Another name is Kugelberg-Welander disease. It causes muscle weakness in mid-childhood. While many can stand and walk earlier on without much help, as the condition progresses over time, walking and climbing stairs tend to become increasingly difficult for them. Most individuals suffering from this condition tend to require wheelchair assistance later in their lives. Unlike other types, they usually have normal life span.
Type IV
It is rare and usually manifests in early adulthood. Patients often experience mild to moderate muscle weakness, tremors, and very mild breathing problems.
Management
The management of SMA varies based upon the severity and type. In the most severe forms (types 0/1), individuals have the greatest muscle weakness requiring prompt intervention. Whereas the least severe form (type 4/adult onset), individuals may not seek the certain aspects of care until later (decades) in life. While types of SMA and individuals among each type may differ, therefore specific aspects of an individual's care can differ.
Medication
Nusinersen (marketed as Spinraza) is used to treat spinal muscular atrophy. It is given directly to the central nervous system using an intrathecal injection. Nusinersen prolongs survival and improves motor function in infants with SMA. It was approved for use in the US in 2016, and for use in the EU in 2017.
Onasemnogene abeparvovec (marketed as Zolgensma) was first approved in the US in May 2019 as an intravenous formulation for children below 24 months of age. Approval in the European Union, Japan and other countries followed, albeit often with different approval scopes.
Risdiplam (marketed as Evrysdi) is a medication taken by mouth in liquid form. Risdiplam was first approved for medical use in the United States in August 2020 and has since been approved in over 30 countries.
Breathing
The respiratory system is the most common system to be affected and the complications are the leading cause of death in SMA types 0/1 and 2. SMA type 3 can have similar respiratory problems, but it is more rare. Complications arise due to weakened intercostal muscles because of the lack of stimulation from the nerve. The diaphragm is less affected than the intercostal muscles. Once weakened, the muscles never fully recover the same functional capacity to help in breathing and coughing as well as other functions. Therefore, breathing is more difficult and pose a risk of not getting enough oxygen/shallow breathing and insufficient clearance of airway secretions. These issues more commonly occur while asleep, when muscles are more relaxed. Swallowing muscles in the pharynx can be affected, leading to aspiration coupled with a poor coughing mechanism increases the likelihood of infection/pneumonia. Mobilizing and clearing secretions involve manual or mechanical chest physiotherapy with postural drainage, and manual or mechanical cough assistance device. To assist in breathing, Non-invasive ventilation (BiPAP) is frequently used and tracheostomy may be sometimes performed in more severe cases; both methods of ventilation prolong survival to a comparable degree, although tracheostomy prevents speech development.
Nutrition
The more severe the type of SMA, the more likely to have nutrition related health issues. Health issues can include difficulty in feeding, jaw opening, chewing and swallowing. Individuals with such difficulties can be at increase risk of over or undernutrition, failure to thrive and aspiration. Other nutritional issues, especially in individuals that are non-ambulatory (more severe types of SMA), include food not passing through the stomach quickly enough, gastric reflux, constipation, vomiting and bloating. Therein, it could be necessary in SMA type I and people with more severe type II to have a feeding tube or gastrostomy. Additionally, metabolic abnormalities resulting from SMA impair β-oxidation of fatty acids in muscles and can lead to organic acidemia and consequent muscle damage, especially when fasting. It is suggested that people with SMA, especially those with more severe forms of the disease, reduce intake of fat and avoid prolonged fasting (i.e., eat more frequently than healthy people) as well as choosing softer foods to avoid aspiration. During an acute illness, especially in children, nutritional problems may first present or can exacerbate an existing problem (example: aspiration) as well as cause other health issues such as electrolyte and blood sugar disturbances.
Orthopaedics
Skeletal problems associated with weak muscles in SMA include tight joints with limited range of movement, hip dislocations, spinal deformity, osteopenia, an increase risk of fractures and pain. Weak muscles that normally stabilize joints such as the vertebral column lead to development of kyphosis and/or scoliosis and joint contracture. Spine fusion is sometimes performed in people with SMA I/II once they reach the age of 8–10 to relieve the pressure of a deformed spine on the lungs. Furthermore, immobile individuals, posture and position on mobility devices as well as range of motion exercises, and bone strengthening can be important to prevent complications. People with SMA might also benefit greatly from various forms of physiotherapy and occupational therapy.
Orthotic devices can be used to support the body and to aid walking. For example, orthotics such as AFOs (ankle foot orthoses) are used to stabilise the foot and to aid gait, TLSOs (thoracic lumbar sacral orthoses) are used to stabilise the torso. Assistive technologies may help in managing movement and daily activity and greatly increase the quality of life.
Other
Although the heart is not a matter of routine concern, a link between SMA and certain heart conditions has been suggested.
Children with SMA do not differ from the general population in their behaviour; their cognitive development can be slightly faster, and certain aspects of their intelligence are above the average. Despite their disability, SMA-affected people report high degree of satisfaction from life.
Prognosis
In the absence of pharmacological treatment, people with SMA tend to deteriorate over time. Recently, survival has increased in severe SMA patients with aggressive and proactive supportive respiratory and nutritional support.
If left untreated, the majority of children diagnosed with SMA type 0 and 1 do not reach the age of 4, recurrent respiratory problems being the primary cause of death. With proper care, milder SMA type I cases (which account for approx. 10% of all SMA1 cases) live into adulthood. Long-term survival in SMA type I is not sufficiently evidenced; however, as of 2007 advances in respiratory support seem to have brought down mortality.
In untreated SMA type II, the course of the disease is slower to progress and life expectancy is less than the healthy population. Death before the age of 20 is frequent, although many people with SMA live to become parents and grandparents. SMA type III has normal or near-normal life expectancy if standards of care are followed. Type IV, adult-onset SMA usually means only mobility impairment and does not affect life expectancy.
Images for kids
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X-ray showing bell-shaped torso due to atrophy of intercostal muscles and using abdominal muscles to breathe. Bell-shaped torso is not specific to individuals with SMA.
See also
In Spanish: Atrofia muscular espinal para niños
