The different types of spinal muscular atrophy may present differently but clinical symptomatology may be similar to some extent.
The following system-wise presentation is commonly in seen in SMAs:
Head and Neck: Sucking and swallowing ability is impaired.
Abdomen: Hypotonic abdominal muscles may be observed in supple babies.
Extremities: Occasional tremors of fingers and muscular fasciculation may be observed in chronic infantile forms of SMA. Pseudohyperthrophy of gastrocnemius muscle (calf muscle) may be seen in SMA II.
Neurologic: Developmental and motor function delay are evident in SMA type 2. Late stage SMA may present with poor deep tendon reflexes.
The following workup and testing methods are implored in cases of spinal muscular atrophy:
A genetic panel for SMN 1 sequencing and coding is amply suggested in cases of infantile SMA suspects . Amniocentesis of the fetal chorionic villi has a sensitivity rating of 88% to 99% in the prenatal diagnosis of SMA. Recent studies reveal that carrier detection rating for SMA may rise to 90% .
The laboratory determination of creatine kinase (CK) level may be a helpful tool in a comprehensive SMA work up. Type 1 SMA will arbitrarily present with a normal CK level while the other forms may show CK elevations.
The use of an electromyography (EMG) and nerve conduction studies may be helpful in the diagnosis of SMA. Muscles which are not clinically affected will show signs of denervation with EMG while nerve conduction remains normal.
There is no available cure for SMA to date. However, there are supportive treatment options to allay the discomforts that inherently affect the SMA patients:
The relative morbidity and mortality rates of SMA varies inversely with age of onset. The SMA type 1 in Werdnig-Hoffman disease carries the worst prognosis with a very high mortality rate. Life expectancy of the patient is usually unaffected with the milder forms of SMA (type 3 and type 4).
Some genetic studies point to prognosticate prenatal occurrence of SMA via amniocentesis. The findings of severe SMA by genetic studies may give some mothers the option for therapeutic abortion in some liberal countries.
The following clinical disorders are the established complications associated with spinal muscular atrophy:
Spinal muscular atrophy is transmitted via an autosomal-recessive gene from both parents, meaning the mother and the father will not convey any symptoms of the disease. The offspring will carry the SMA gene defect through a homozygous deletion type of inheritance.
The inherited genetic defects on chromosome 5q11.2-13.3 are generally associated with spinal muscular atrophy type 1 to 3 . Defects in genetic SMA are not exclusive to peripheral nerves but it involves the central nervous system (CNS) as well. There is a clinical variant of SMA, known as autosomal-dominant spinal muscular atrophy characterized by a predominantly lower limb weakness and muscle wasting .
In the United States, SMA represent the next most common autosomal-recessive genetic disorder following cystic fibrosis. The acute form of SMA in infants occurs in 1 out of 10,000 live births, while the chronic SMAs becomes evident in 1 out of 24,000 births. The chronic infantile type of SMA accounts to 50% of all cases .
Spinal muscular atrophy expresses in 1 out of 10,000 live births worldwide . The mortality rate of acute infantile SMA (type 1) reaches 95% with a 7 month mean survival average.
The familial spinal muscular atrophy is represented by two survival motor neurons (SMN1 and SMN2) . In more than 95% of SMA cases there has been an evident homozygous gene disruption in SMN1 on the small arm loci of chromosome 5q.
These pathologic phenomenon is grossly brought about by spontaneous mutation and gene deletion. The missing SMN1 in the genetic defect will allow SMN2 to generate the missing protein for the spinal cord development although it can only come up with 10% of the actual protein chain length .
Genetic counselling for carrier parents may avert the emergence of an affected sibling. The prenatal amniocentesis of the fetal chorionic villus may help attending physicians prepare for any untoward eventualities during the baby’s delivery. Prompt diagnosis and early intervention is the key in reducing morbidity and mortality.
Spinal muscular atrophy or SMA is a hereditary disease characterized by progressive musclar weakness due to deterioration of the lower motor neuron (anterior horn) cells of the spinal cord including the motor nuclei of the central nervous system (brainstem).
The pathology is mainly on the motor neurons connecting the spinal cord and the brain to the muscles of the body. The more common types of spinal muscular atrophy include: Werdnig-Hoffman disease or SMA type 1 (infantile type of acute onset), SMA type 2 (chronic infantile type), Kugelberg-Welander disease or SMA type 3 (chronic juvenile onset), and the SMA type 4 (adult onset).
Spinal muscular atrophy or SMA is a hereditary disease characterized by the progressive musclar weakness due to the deterioration of the lower motor neuron (anterior horn) cells of the spinal cord including the motor nuclei of the central nervous system (brainstem).
It is due to autosomal-recessive genetic inheritance.
Patients diagnosed with spinal muscular atrophy should be submitted to rigorous pediatric neurology follow-ups for the early classification of the disease.
Treatment and follow up
The third and fourth type of SMA may be compatible to normal living till adulthood. Offspring from patients who make it to adulthood may carry the recessive gene and should be subjected to parental genetic counselling in the future.