Understanding Spinal Muscular Atrophy (SMA)
Spinal Muscular Atrophy known as SMA is a life interchanging and usually fatal genetic disorder that attacks motor neurons. Children with Type 1 have restricted movement, inconvenience breathing and feeding. Tragically whenever left untreated, children suffering from SMA may not make it to their subsequent birthday.
SMA is an autosomal passive neuromuscular disease portrayed by degeneration of alpha motor neurons in the spinal cord, bringing about progressive proximal muscle weakness and paralysis. The disease is characterized by generalized muscle weakness and atrophy prevailing in proximal limb muscles, and the aggregate is grouped into four grades of severity – SMA I, SMA II, SMA III and SMA IV – based on age of onset and motor function achieved.
It is an intriguing genetic neuromuscular disease caused by a mutation in the survival motor neuron (SMN1) gene. This gene is responsible for producing survival motor neuron (SMN) protein, which keeps up with the wellbeing and normal function of motor neurons. The degeneration of motor neurons prompts a gradual decrease in the mass and strength of muscles.
SMA influences the part of the nervous system that controls voluntary muscle movement. It has a deficiency of significant cells in the spinal cord called motor neurons, which are fundamental for muscle strength and movement. These motor neurons direct muscle activity by conveying signal from the central nervous system, which is the part of the body’s nervous system that includes the brain and spinal cord.
The deficiency of functioning motor neurons leads to progressive muscle weakness and atrophy, as muscles stop receiving signals from the central nervous system. SMA type-I is the most severe and common type, which accounts for about 50% of patients diagnosed with SMA. Classically, infants with SMA type-I have onset of clinical signs before six months of age and never acquire the ability to sit unsupported. If no intervention is provided, usually these babies do not survive beyond the first two years.
These affected patients have profound hypotonia, symmetrical flaccid paralysis and often no head control. Spontaneous mobility is usually poor and antigravity movements of limbs are not typically observed. In the most severe forms, reduced intrauterine movements suggest prenatal onset of the disease and present with severe weakness and joint contractures at birth and has been labeled as SMN o. Some of these children may also show up congenital bone fractures and extremely thin ribs.
Although SMA is characterized by certain signs and symptoms, there are other conditions showing up similar symptoms but with different genetic causes. Therefore, diagnosing SMA depends on genetic testing. Conditions with similar symptoms include:
• Spinal Muscular Atrophy with Respiratory Distress (SMARD) – SMARD affects the upper spinal cord neurons instead of the lower motor neurons. Kids with SMARD normally have low birth weight and experience side effects inside the initial 3-6 months, including extreme respiratory distress because of paralysis of the diaphragm.
• Distal Hereditary Motor Neuropathy – This is an incredibly rare autosomal dominant genetic disease, which implies that only one inherited copy of the abnormal gene is needed for the disease to happen. It influences the nerve cells in the spinal cord and presents as weakness and wasting that begins in the muscles of the upper and lower limbs and later spreads to different muscles.
• Kennedy’s Disease (KD) – Unlike Spinal Muscular Atrophy, which influences the motor neurons, KD influences both lower motor and sensory neurons and occurs only in males. It is a disease of the X chromosome.
Diagnosis of SMA can be confirmed by a physical examination which looks at your child’s present symptoms as well as a gene test such as the SMN (Survival Motor Neuron) test. In few cases, when the SMN gene test is not possible or does not show any abnormality, other tests such as an Electromyography (EMG) or a muscle biopsy may be used to confirm diagnosis.
At Chetna Foundation, our specialists provide expert care for patients with Spinal Muscular Atrophy.
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