Spinal muscle atrophyorspinal muscular atrophy(SMA) is a genetic disorder that can affect babies, children, and adults. A person with this disorder will feel weak in some parts of the body, especially the hands and feet.
SMA has different types and has various effects on sufferers. One of them can even cause death.
Definition of Spinal Muscle Atrophy
Spinal muscular atrophy(SMA) is a hereditary disease that attacks the nerves and muscles, causing the muscles to become increasingly weak. This condition mostly affects infants and children, although in some cases it can also develop in adults.
Symptoms and prognosis of SMA vary depending on the type. Gene replacement and disease modification therapies offer hope for a cure.
Types of Spinal Muscular Atrophy
Here are 4 main typesspinal muscle atrophy:
Type 1 or Severe
About 60% of people with this disorder have SMA type 1. This condition is also known as SMA type 1 disease.Werdnig-Hoffman.Symptoms appear at birth or within the first six months of the baby’s life.
Babies with SMA type 1 have difficulty swallowing and sucking. They do not have the same development as other babies of that age, such as lifting their heads or sitting up.
As muscles continue to weaken, children become more susceptible to respiratory infections and collapsed lungs (pneumothorax). Most children with SMA type 1 die before reaching the age of 2.
Type 2 or Intermediate
Symptoms of SMA type 2 or also known as SMA diseaseDubowitzappears when a child is between 6 and 18 months old. This type tends to affect the lower limbs. Children with SMA type 2 may be able to sit, but not walk. Most children with this type of SMA survive to adulthood.
Type 3 or Mild
Signs of SMA type 3 or also known asKugelbert-Welanderor adolescent-onset SMA appears after the first 18 months of a child’s life. Some people with type 3 have no signs of the disease until early adulthood.
Symptoms of SMA type 3 include mild muscle weakness, difficulty walking and frequent respiratory infections. Over time, symptoms may affect a child’s ability to walk or stand. SMA type 3 does not significantly shorten life expectancy.
Type 4 or Adult
The rare adult form of SMA usually doesn’t appear until the mid-30s. Symptoms of muscle weakness develop slowly, so most people with type 4 can still move around normally and live normal lives.
Symptoms of Spinal Muscle Atrophy
The signs that a child has SMA and when they first appear depend on the type of disease they have. Common symptoms include:
- Weak arms and legs
- Movement problems, such as difficulty sitting, crawling or walking
- Muscle twitching or shaking (tremor)
- Bone and joint problems, such as an unusually curved spine (scoliosis)
- Difficulty swallowing
- Difficulty breathing
Children withspinal muscle atrophyhave no problems with intelligence or learning disabilities.
Causes of Spinal Muscle Atrophy
Causes of all types spinal muscle atrophy is a mutation in the SMN1 gene. While the severity of the condition and the type that develops can be determined from the number of copies of the SMN2 gene.
Both the SMN1 and SMN2 genes provide instructions for making a protein called the survival motor neuron (SMN) protein. Normally, most of the functional SMN protein is produced from the SMN1 gene, with a small amount produced from the SMN2 gene.
Several different versions of the SMN protein are produced from the SMN2 gene, but only one version is functional, while the others are smaller and break down quickly. The SMN protein is one of a group of proteins called the SMN complex and is important for the maintenance of motor neurons.
Motor neurons send signals from the brain and spinal cord that tell skeletal muscles to tense (contract), allowing the body to move. Most people with SMA are missing part of the SMN1 gene, which interferes with the production of the SMN protein.
SMN protein deficiency causes motor neurons to die, and as a result, signals are not transmitted between the brain and muscles. Muscles cannot contract without receiving signals from the brain, so many skeletal muscles become weak and wasted. This condition is what causes the symptoms of SMA.
Typically, people have two copies of the SMN1 gene and one to two copies of the SMN2 gene in each cell, but the number of copies of the SMN2 gene varies. Some people have up to eight copies.
People with SMA who have multiple copies of the SMN2 gene are associated with less severe outcomes later in life. The SMN protein produced by the SMN2 gene can help compensate for the protein deficiency caused by mutations in the SMN1 gene.
People with type 1 SMA typically have one or two copies, those with type 2 typically have three copies, those with type 3 have three or four copies, and those with type 4 have four or more copies. Many other unknown factors also contribute to the variable severity of SMA.
Frequency of Occurrence
The disease affects 1 in 8,000 to 10,000 people worldwide. SMA type 1 is the most common type, accounting for about half of all cases. Types 2 and 3 are the next most common and type 4 is the least common.
Risk Factors
Children with SMA are also caused by genetic problems inherited from their parents. Therefore, consult a doctor when planning a pregnancy if you have experienced the following:
- Have had a child with SMA before
- Having a history of the same condition in the family
- Your partner has a history of the same condition in his or her family.
Your doctor may refer you to a genetic counselor to discuss the risk of the condition affecting future pregnancies and what tests you should have.
Diagnosis
Here are some ways your doctor can diagnose SMA:
- Blood tests : Enzyme and protein blood tests can check for high creatine kinase levels. Deteriorating muscles release these enzymes into the bloodstream.
- Genetic testing : This blood test identifies problems with the SMN1 gene. As a diagnostic tool, genetic testing is 95% effective in finding an altered SMN1 gene.
- Nerve conduction tests : An electromyogram (EMG) measures the electrical activity of muscles and nerves.
- Muscle biopsy : This is one of the least common procedures. It involves removing a small amount of muscle tissue and sending it to a lab for testing. A biopsy may show atrophy, or loss of muscle.
Prenatal testing can also determine if your unborn baby has the disease. Especially if you have a family history of SMA. It is important to note that the following tests increase the risk of miscarriage.
Prenatal testing for SMA includes:
- Amniocentesis : During amniocentesis, your obstetrician will insert a thin needle into your abdomen to remove a small amount of fluid from the amniotic sac. A lab specialist or pathologist will then check the fluid for SMA. This test is done after the 14th week of pregnancy.
- Chorionic villus sampling (CVS) : Your obstetrician removes a small tissue sample from the placenta through the cervix or abdomen. A pathologist examines the sample for SMA. CVS can occur as early as the 10th week of pregnancy.
Handling
There is no cure for SMA. However, there are several treatments that can be done depending on the type of SMA and its symptoms.
Many people with SMA benefit from physical and occupational therapy and assistive devices, such as orthopedic braces, crutches, walkers, and wheelchairs.
In addition, the following treatments may also help:
- Disease-modifying therapy : This therapy uses drugs that stimulate the production of the SMN protein. Nusinersen (Spinraza®) is a drug used for children ages 2 to 12. The doctor injects the drug into the space around the child’s spinal canal. A different drug, risdaplam (Evrysdi®), helps adults and children older than two months. It is taken orally.
- Gene replacement therapy : Children under two years of age may benefit from a single intravenous (IV) infusion of a drug called onasemnogene abeparvovec-xioi (Zolgensma®). This therapy replaces the missing or defective SMN1 gene with a functioning one.
Possible Complications
Over time, a person with SMA will experience progressive muscle weakness and loss of muscle control. Possible complications include:
- Fractures, hip dislocations and scoliosis (curvature of the spine).
- Malnutrition and dehydration due to feeding and swallowing problems which may require a feeding tube.
- Pneumonia and respiratory tract infections.
- Weak lungs and breathing problems that may require breathing assistance (ventilation).
Prevention
Spinal muscular atrophyis an inherited disease. If you or your partner carries the mutated gene that causes the disease, a genetic counselor can explain the chances of your child having SMA or being a carrier.
Therefore, you may be able to take steps before pregnancy to lower your risk of passing SMA to your child. The process of preimplantation genetic diagnosis (PGD) can identify embryos that do not have the mutated gene.
The way it works is that your doctor will implant a healthy embryo during in vitro fertilization (IVF) . This can ensure that your child will have two healthy SMN1 genes and will not get SMA.
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Republished with permission from theAsianparent Indonesia
