It is a rare NEUROMUSCULAR DISORDER, that results in loss of motor neurons and progressive muscle wasting.
(Motor neurons- are nerve cells responsible for carrying signals away from CNS that is towards muscle to cause movements.)
After Cystic fibrosis SMA is 2nd most common fatal autosome recessive disorder with an estimated incidence of 1 in 6000 to 1 in 10,000 live births.
SMA is occur due to an abnormality in the SMN1 gene, which encodes a protein SMN, which is necessary for the survival of motor neurons.
Individuals who are diagnosed with SMA have insufficient levels of SMN protein which leads to loss of motor neurons in the spinal cord, which produces weakness and wasting of skeletal muscles.
SMN2 gene is a disease-modifying gene.
INHERITANCE-
Genes are present on chromosome. Like chromosomes, genes are also inherited from both the parents half from mother and half from father.
Genetic conditions like SMA caused by fault in the genes.
Chromosomes carry DNA and genes are the specific region in DNA.
In case of SMA, there is SMN1 gene and SMN2 gene, SMN1 gene is more responsible for function as compared to SMN2 gene.
Generally, person carries two SMN1 gene copies, that is one from each parent, copies of SMN2 gene can vary from 0-8, mostly there are two copies but because of duplication number can increase.
Both SMN gene encodes for a protein known as SMN protein which is responsible for motor neuron function.
More than 95% of SMA is chromosome 5 related.
SMN genes ( both 1&2) are present on chromosome 5 at 5q13 region. SMN gene consist of 9 exons( exons are segment of DNA or RNA molecule containing information coding for a protein).
SMN1 gene produce 100% full length SMN protein, whereas SMN2 gene produce less than 20% full length SMN protein.
The absence or mutation of SMN1 gene copies lead to SMA.( eg. deletion of exons, missing gene etc.)
More the number of SMN2 gene, the more milder or less severe will be the course of SMA.
Chances of having a child with SMA depend on both the partners. Hence, with each pregnancy there is 25% chances of child having SMA. Having one child with SMA it does not get change , chances of having SMA is still there.
SYMPTOMS-
1)Most of the children with SMA tend to have delayed developmental milestones eg. lack of neck control movement in an infant
2) Muscle weakness- Is the primary symptom, usually affects both sides of the body. Degree of weakness usually depend upon which '' TYPE'' of SMA the person has.
Usually, muscles closure to the center of body ( proximal muscles) are more affected than the muscles which are away from the center (distal muscles).
for eg; muscles of thigh are more affected than the muscles of lower leg or feet.
3)SMA has a huge impact on functionality of person-
a. Sitting up-
In case of SMA type0&1 child can never develop the ability to sit up unsupported.
b. Standing
Children with SMA type2 rarely develop ability to stand.
In case of SMA type 3 will be able to stand, but can have problems in moving.
c. Walking
In case SMA type 0-2 will never develop ability to walk.
4) Respiratory problems like, problem in breathing could occur because of weak respiratory muscles.
Rare symptoms- i) Tremors (involuntary movement)
ii) Dysphagia
iii) Bed sores due to decreased physical movement and prolonged immobility.
iv) Respiratory infections due to weak breathing.
v) In severe cases, there can be weakness in hands, fingers, toes.
To know more about the Child Developmental Milestones Click here.
Types of SMA-
(A) SMA-Type 0
Most severe form of SMA.
- Type 0 affects the baby while still in womb by reduced fetal movement in later stage of pregnancy.
- Infants present with i) severe weakness,
ii) extremely weak muscle tone,
iii) respiratory failure
besides these symptoms child commonly have a weak cry, problems in swallowing, facial weakness, joint contractures, heart defects.
- Child can die before birth or within few months of life.
(B) SMA-Type 1 ( Werding- Hoffman disease)
Most common form of condition.
- Symptoms:-
1) Children with this type may have swallowing problems that can lead to difficulty in feeding and poor health.
2) Can also have breathing problems due to weakness of respiratory muscles. That is the reason due to which, most children with SMA Type-1 do not survive past early childhood because of respiratory failure.
3) Babies typically have general muscle weakness, weak cry, breathing distress.
4) Child with this type of SMA never learn to sit.
- Babies have 2-3 copies of the SMN-2 gene.
Note-
It is not necessary that the child with this type of SMA will die between 2-4 years of age, The survival rate can increase with proper respiratory care and nutrition.
(C) SMA Type-II-
- Symptoms are less severe than Type-1 SMA but can get worsen over time.
2) Usually face and eye
3) As the child grows, child can develop scoliosis.
- Although, SMA type-II has shortened life expectancy but with proper care one can live long.
(D) SMA Type-III-
Also known as Kugelberg Welander Disease.
- SMA type -III accounts for 30% of the overall SMA case.
- Symptoms usually appear between the age of 18 months and adulthood.
- Affected individuals achieve independent mobility.
(E) SMA Type-IV-
- is a mild form of SMA, accounts for 5% of SMA cases.
- The person affected with this form of SMA has 4-8 copies of the SMN2 gene.
- Affected individuals maintain mobility throughout their lives.
- Its symptoms include leg weakness, tremors in fingers.
The lifespan of the person remains
(F) SMA-LED-
Rare condition.
- SMA with lower extremity predominance characterized by, muscle weakness and wasting in lower limbs.
- Features- i)Affected individuals have waddling gait or unsteady walk.
ii) have difficulty rising from seated position and climbing stairs
iii) Joint deformities in knees, hip, feet and ankle can occur
iv) Some people may also have weakness in upper limb muscles.
- In most cases the symptoms came in infancy or early childhood, about one quarter of affected individuals do not develop muscle weakness until adulthood.
- People with severe symptoms may require a wheelchair for mobility.
It is caused by mutation in DYNC1H1 gene or BICD2 gene.
When this condition is caused by mutation in DYNC1H1 it is often known as SMA-LED Type 1 and when it is caused by mutation in BICD2 gene it is known as SMA-LED
Person have this type of SMA usually have a normal life expectancy.
Note-
Currently there is NO TREATMENT for this rare condition.
DIAGNOSIS-
(I) Carrier test-
used to identify asymptomatic person who is a carrier for this condition. Testing is usually initiated on the basis of family history.
(II) Prenatal test-
are test done on pregnant women, to detect any potential issues with baby before birth.
Prenatal test in case of SMA is available. Some are as follows-
a) Chronic villus sampling-
- test done between 10-13 weeks of pregnancy.
- DNA sample is taken from placenta.
- test done between 14-20 weeks of pregnancy.
- DNA sample is taken from amniotic fluid in your uterus.
Early diagnosis help in getting treatment which can prevent the condition to get worsen.
TREATMENT-
- There is no specific cure for SMA.
- Supportive management includes:
(i) Respiratory care,
(ii) ensuring adequate nutrition,
(iii) Treatment of gastroesophageal reflex,
(iv) Orthopedic care and rehabilitation,
(v) Counselling and family education,
(vi) Physiotherapy,
(viii) Occupational therapy
In severe cases, ventilators can also required.
- Gene therapy for SMA-
1)Nusinersen marketed as, Spinraza- is the first disease-modifying therapy approved for SMA and has shown many benefits.
2) Onasemnogene abeparvovec marketed as, Zolgensma - treats the person by replacing the
Genetic counseling-
Genetic counseling is a very important component for support of family with SMA.
It gives information about how genetic condition might affect someone and their family.
Genetic counsellor or other healthcare professional will collect personal and family history of the person. This information use to determine how likely it is that person or his/her family members has a genetic condition. On the basis of information, genetic counselor help one decide whether genetic test is required or not.
Therefore, if a couple has a history of SMA in their family and wanted to know whether he or she is a carrier for this disease or not, can go to the genetic counselors or if a couple had a child with SMA and is planning for another child can also refer to genetic counselors.
NOTE-
It is very important to indulge children or adults with SMA in various activities so that-
1) Joint stiffness can be prevent.
2) Joints can be strengthened
3) Blood circulation can be improved
4) Normal activity of person can be preserved.
It is very important to SPREAD AWARENESS about SMA as most of us are still unaware about it.
If we come together to spread this little information with everyone, it might help someone.
Advertising about SMA is also a great source for spreading awareness.
In many areas there is still, lack of digitalization i.e. people still not have access to internet, phones, computers etc. Therefore, it is very necessary to ORGANIZE CAMPAIGNS TO EDUCATE PEOPLE ABOUT SMA.
Here's a small note for everyone who has SMA-
Many of us can't even imagine that what kind of challenges you had faced or is facing even right now while reading this. You are definitily more than what people think about you.
YOU ARE AWESOME!! And remember you can do anything in your life.
To dear parents-
I can't even imagine that what kind of pain you have gone through, when you first time heard that your child is diagnosed with SMA. But you know what you all are, you are SUPERHEROES for your child.
Please do not loose hope, Everything will get better with time and you are very Strong.
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