About infantile spinal muscular atrophy type i
What is infantile spinal muscular atrophy type i?
The spinal muscular atrophies (SMAs), are characterized by degeneration of nerve cells (motor nuclei) within the lowest region of the brain (lower brainstem) and certain motor neurons in the spinal cord (anterior horn cells) leading to muscle weakness of the truncal, and extremity muscles initially, followed by chewing, swallowing and breathing difficulties. Motor neurons are nerve cells that transmit nerve impulses from the spinal cord or brain (central nervous system) to muscle or glandular tissue.
Approximately 80 percent of individuals with SMA fall into the severe category (Werdnig-Hoffman disease or SMA1). Infants with SMA1 experience severe weakness before 6 months of age, and the patient never achieves the ability to sit independently when placed. Muscle weakness, lack of motor development and poor muscle tone are the major clinical manifestations of SMA1. Infants with the gravest prognosis have problems sucking or swallowing. Some show abdominal breathing in the first few months of life. Abdominal breathing is noted when the abdomen protrudes during inspiration. Normally, the chest expands during inspiration as the intercostal muscles (the muscles between the ribs) expand during inspiration. Abdominal breathing occurs when the intercostal muscles are weak and the diaphragm muscle is responsible for inspiration. Movement of the diaphragm (the muscle between the chest and abdomen) expands causing the abdomen to move during the inspiration cycle. Twitching of the tongue is often seen (fasciculations). Cognitive development is normal. Most affected children die before 2 years of age but survival may be dependent on the degree of respiratory function and respiratory support.
The different subtypes, SMA 0-4 are based on the age of onset of symptoms and the course and progression of the disease. SMA represents a continuum or spectrum of disease with a mild end and a severe end. SMA0 patients are extremely weak at birth, require immediate artificial ventilation and will never breathe independently. Werdnig-Hoffman disease, which is also known as spinal muscular atrophy type 1 (SMA1) or acute spinal muscular atrophy, refers to individuals who have symptom onset prior to 6 months of age. SMA 2 patients will show symptoms prior to age 1 year, will sit but never walk. SMA 3 patients (Kugelberg-Welander disease) will show symptoms after age 1, and will walk for a period of time prior to loss of motor abilities. SMA 4 patients will not develop symptoms much before age 10 years.
All the SMAs are inherited as an autosomal recessive trait. Molecular genetic testing has revealed that all types of autosomal recessive SMA are caused by disruptions or errors (mutations) in the SMN1 (survival motor neuron 1) gene on chromosome 5.
What are the symptoms for infantile spinal muscular atrophy type i?
SMA is classified into five types, based on the age when symptoms appear and the severity of the condition. All types of SMA are progressive, which means they tend to get worse over time.
Type 0 SMA is the rarest and most severe type.
When a baby has type 0 SMA, the condition may be detected before they’re born, while they’re still developing in the womb.
Babies born with type 0 SMA have extremely weak muscles, including weak respiratory muscles. They often have trouble breathing.
Most infants born with type 0 SMA don’t survive for more than 6 months.
Type 1 SMA is also known as Werdnig-Hoffmann disease or infantile-onset SMA. It’s the most common type of SMA, according to the National Institutes of Health (NIH).
When a baby has type 1 SMA, they will likely show signs and symptoms of the condition at birth or within 6 months of being born.
Children with type 1 SMA typically can’t control their head movements, roll over, or sit without help. Your child may also have difficulty sucking or swallowing.
Children with type 1 SMA also tend to have weak respiratory muscles and abnormally shaped chests. This can cause serious breathing difficulties.
Many children with this type of SMA don’t survive past early childhood. However, new targeted therapies may help improve the outlook for children with this condition.
Type 2 SMA is also known as Dubowitz disease or intermediate SMA.
If your baby has type 2 SMA, signs and symptoms of the condition will likely appear between the ages of 6 and 18 months.
Children with type 2 SMA typically learn to sit on their own. However, their muscle strength and motor skills tend to decline over time. Eventually, they often need more support to sit.
Children with this type of SMA typically can’t learn to stand or walk without support. They often develop other symptoms or complications as well, such as tremors in their hands, unusual curvature of their spine, and breathing difficulties.
Many children with type 2 SMA survive into their 20s or 30s.
Types 3 and 4
In some cases, babies are born with types of SMA that don’t produce noticeable symptoms until later in life.
Type 3 SMA is also known as Kugelberg-Welander disease or mild SMA. It typically appears after 18 months of age.
Type 4 SMA is also called adolescent- or adult-onset SMA. It appears after childhood and tends to cause only mild to moderate symptoms.
Children and adults with type 3 or type 4 SMA may experience difficulties with walking or other movements, but they tend to have normal life expectancies.
What are the causes for infantile spinal muscular atrophy type i?
SMA is caused by mutations in the SMN1 gene. The type and severity of the condition is also affected by the number and copies of the SMN2 gene that a baby has.
To develop SMA, your baby must have two affected copies of the SMN1 gene. In most cases, babies inherit one affected copy of the gene from each parent.
The SMN1 and SMN2 genes give instructions to the body for how to produce a type of protein known as the survival motor neuron (SMN) protein. SMN protein is essential to the health of motor neurons, a type of nerve cell that passes signals from the brain and spinal cord to muscles.
If your baby has SMA, their body is unable to produce SMN proteins properly. This causes motor neurons in their body die. As a result, their body can’t properly send motor signals from their spinal cord to their muscles, which leads to muscle weakness, and eventually causes muscle wasting due to lack of use.
What are the treatments for infantile spinal muscular atrophy type i?
There is currently no known cure for SMA. However, multiple treatments are available to help slow the progression of the disease, relieve symptoms, and manage potential complications.
To provide the support that your baby needs, their doctor should help you assemble a multidisciplinary team of healthcare professionals. Regular checkups with members of this team are essential for managing your child’s condition.
As part of their recommended treatment plan, your child’s health team may recommend one or more of the following:
- Targeted therapy. To help slow or limit the progression of SMA, your child’s doctor may prescribe and administer the injectable medications nusinersen (Spinraza) or onasemnogene abeparvovec-xioi (Zolgensma). These medications target underlying causes of the disease.
- Respiratory therapy. To help your baby breathe, their health team may prescribe chest physiotherapy, mechanical ventilation, or other respiratory treatments.
- Nutritional therapy. To help your baby get the nutrients and calories they need to grow, their doctor or dietitian may recommend nutritional supplements or tube feeding.
- Muscle and joint therapy. To help stretch their muscles and joints, your child’s health team may prescribe physical therapy exercises. They may also recommend the use of splints, braces, or other devices to support healthy posture and joint positioning.
- Medications. To treat gastroesophageal reflux, constipation, or other potential complications of SMA, your child’s health team may prescribe one or more medications.
As your child gets older, their treatment needs will likely change. For example, if they have severe spinal or hip deformities, they may need surgery in later childhood or adulthood.
If you’re finding it emotionally difficult to cope with your baby’s condition, let your doctor know. They may recommend counseling or other support services.
Your baby’s physical therapist, occupational therapist, or other members of their health team may encourage you to invest in special equipment to help care for them.
For example, they may recommend:
- light-weight toys
- special bath equipment
- adapted cribs and strollers
- molded pillows or other seating systems and postural supports
What are the risk factors for infantile spinal muscular atrophy type i?
Infantile spinal muscular atrophy type I (SMA) is a genetic disorder that results in progressive muscle weakness in infants and children, typically before the age of 2. This disease is caused by a mutation in the SMN1 gene, which produces a protein called survival motor neuron. This protein is essential for normal nerve cell function.
1. The first signs of SMA typically begin between 6 and 18 months of age and include difficulty lifting the head or sitting without support, decreased movement, and difficulty feeding.
2. There are three types of SMA: type I, type II and type III, which differ based on their symptoms and severity. The most severe form is infantile spinal muscular atrophy type I, which causes paralysis before 12 months of age. All types of SMA are incurable but can be managed with physical therapy, occupational therapy and assistive devices to help with mobility issues such as walking or standing upright for long periods of time.
3. The risk factors for infantile spinal muscular atrophy type I are not well understood. It is believed that the most common cause of the disease is a mutation in the SMN1 gene, which encodes a protein called survival motor neuron (SMN) protein. The mutated gene prevents production of sufficient levels of SMN protein.
4. In some cases, infantile spinal muscular atrophy type I is inherited from a parent who carries a recessive copy of the SMN2 gene. This means that both parents must be carriers or have one mutant copy of the gene in order for symptoms to occur in their children.
It has also been shown that certain environmental factors may increase your risk of developing infantile spinal muscular atrophy type I. These include:
1. Exposure to viruses that can damage the nervous system, such as cytomegalovirus (CMV), rubella and varicella zoster virus (VZV)
2. Exposure to chemicals that are toxic for nerve cells, such as arsenic or mercury.
Poor head control and failure to sit up,Inability to stand with support,Inability to hold head up when lying on stomach,Difficulty swallowing food or liquids,Muscle weakness (can't lift arms or legs),Smaller muscles than normal for age
Progressive muscle weakness,Limbs that are slightly shorter than normal,Poor head control,Loss of reflexes, such as the ability to grasp things with your hands,Possible breathing problems