Spinal Muscular Atrophy Types
There is a vast spectrum of impairment present in spinal muscular atrophy. The neuromuscular disorder results as the defects in the SMN1 gene appear. The disorder symptoms start appearing from the onset of pregnancy as the fetus suffers from breathing difficulties. Some adults are having SMA suffer from mild weakness in their muscles. The studies show that SMA classification into four common types is more dependent on achieving the highest motor mild stone. The smaller muscles in the human body get weak day by day, and their size also starts diminishing. The most severe form of all the spinal muscular atrophy types is the SMA type 1, commonly known as SMA type 0. SMA type 1 is fatal and rare for the patients and poses severe symptoms. Following are the most common types of spinal muscular atrophy;
SMA Type 1 (Werding-Hoffmann disease)
This type of SMA is evident typically before the age of six months in infants. There is a reduction in movements even in the gestation period, and eventually, the babies are born with breathing problems and spine contractures. In most severe SMN type 1, there is a possibility of newborns’ death in the first year of life. Proper treatment is essential for the kids born with SMN type 1. Some of the common symptoms of SMN type 1 include tongue fasciculations, lack of tendon reflexes, swallowing difficulties, feeding difficulties, impaired breathing, diminished limb movements, and hypotonia (reduction in muscle tone). The infants born with SMA type 1 also developed curvature of the spine or other skeletal muscle abnormalities as they get older. If a child doesn’t seek any treatment, he or she can never sit or stand. There is a majority of SMA type 1 patients who usually die due to the failure of the respiratory system before reaching the age of 12 years. As medicine is growing, there are no disease-modifying treatments available, increasing SMA type 1 patients’ life expectancy. Moreover, the children having SMA type 1 can achieve higher motor skills like walking and sitting by using proactive methods like gene therapy.
SMA type 2 (The intermediate form)
The children having SMA type 2 starts showing their symptoms between the ages of 6 and 12 months; such children are not able to walk or stand without support but can sit unaided. Some children might lose the ability to stay seated independently for a longer time without seeking any treatment. There is an occurrence of some respiratory issues such as hypoventilation, which causes problems with sleep. Each patient of SMA type 2 has variable disease progression if there are not seeking any treatment. There is a reduction in life expectancy, but most children stay alive until their young adulthood. With the use of proactive clinical care, the motor outcomes can be improving for the children with SMA type 2.
SMA Type 3 (Kugelberg-Welendr disease)
The children suffering from SMA type 3 start developing the symptoms after the age of 18 months. The children start walking independently, but they face difficulty running, walking, rising from a chair, or climbing steps. The proximal muscles present near the body’s core significantly closer to the legs suffer the most from the SMA type 3. The SMA type 3 patients mostly suffer from the tremors in their hands, which come and go, thus indicating the impaired signal transduction in the nervous system. There are certain complications, too, due to the SMA type 3 if the patient is not seeking any treatment. The complications like chronic shortening of tendons or muscles around the joints, i.e., joint contracture and spinal cord contracture, might occur in the SMA type 3 patients. The patients cannot move their joint freely, mainly due to muscle tone and weakness reduction. The patients of SMA type 3 are also more prone to develop respiratory problems in their later life. If the patients receive constant proactive clinical care, they can lead an average lifespan. The developmental milestones like fine and gross motor skills, can reach timely if the patient seeks disease-modifying treatments.
SMA type 4
The patients suffering from SMA type 4 start developing the symptoms after 21 years, having moderate to mild symptoms. The most prevailing symptoms are typically proximal muscle weakness and muscle tone wasting. SMA type 4 usually occurs in adulthood, and they can easily manage the symptoms of the disease by stretching or using assistive types of equipment to make their life easier.
Other types of SMA
There are some less common and rare types of SMA, including:
Distal spinal muscular atrophy (DSMA)
This type of spinal muscular atrophy significantly affects the feet, hands, lower legs, and lower arms.
Spinal muscular atrophy with respiratory distress (SMARD)
SMARD is a type of spinal muscular atrophy that appears in the first year of life in the infants and might result in serious respiratory problems, thus causing the baby’s death.
Kennedy’s disease, or spinobulbar muscular atrophy (SBMA)
One of the rare types of spinal muscular atrophy is SBMA, which only affects males and starts in the middle adulthood of the life span. The life expectancy of the patient does not suffer from this type of spinal muscular atrophy.