SMA is a leading inherited cause of death in infants with an approximate incidence of 1/10,000.1 Over recent years, SMA has been widely researched in children. Here, two key experts give their perspective.
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WHAT IS SMA?
SMA is a neuromuscular disease, characterised by degeneration of motor neurons in the spinal cord, causing muscular weakness.2
Mutations in the SMN1 gene result in a shortage of the SMN protein, which is expressed in all cells and found in high concentrations in spinal cord motor neurons.3 The link between a lack of SMN protein and SMA pathology is not fully understood.2
SMA can be classified into subtypes, depending on age of onset and level of motor function achieved.2 SMA can result in early mortality depending on the type, with severely affected infants not surviving past six months of age.4
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“The disease has a wide clinical spectrum.”
Dr Nathalie Goemans
Head of the Neuromuscular Reference Centre, Paediatrics and Child Neurology, University Hospitals Leuven.
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Four subtypes of SMA have been described based on age of onset and level of motor function achieved.2 Find out more about types of SMA.
“All people with SMA have some copies of SMN2 and the number of copies determines the phenotype”
Dr. Eduardo Tizzano
Director of the Department of Clinical and Molecular Genetics, Vall d’Hebron Hospital.
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SMA develops due to the homozygous disruption of the SMN1 gene.1
The carrier frequency is estimated to be 1 in 30-50 in populations of European ancestry, and is considerably lower in some populations of African ancestry.5
SMA can be thought of as a disease of two genes; the SMN1 gene, which is the determinant gene, and the SMN2 gene, which is the modifier gene. Whilst loss of the SMN1 gene is responsible for the pathogenesis of SMA, the severity of the disease is related to the number of copies of SMN2, with more copies resulting in milder disease.3
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SMA is one of the leading genetic causes of infant death worldwide.4 Find out more about the biology and genetics of SMA.
SMA type 1 patients have an early onset of less than 6 months of age. They are unable to sit independently and demonstrate abnormal breathing patterns.
SMA type 2 patients have an age of onset before 18 months of age, and, although weak, with good supportive care and no treatment generally survive into early adulthood.4
SMA type 1 has the highest estimated incidence at birth,6 however – without treatment - the majority of patients with SMA type 1 do not survive beyond two years of age4 so SMA type 2 has a higher estimated prevalence in the population.6
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“Due to the shorter life expectancy, the prevalence is different.”
Dr Nathalie Goemans
Head of the Neuromuscular Reference Centre, Paediatrics and Child Neurology, University Hospitals Leuven.
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Delays in diagnosis cause stress for patients and their families and prevent early treatment,7 so early diagnosis should be prioritised. Learn more about diagnosing SMA.
“Patients are requesting information, and we have to give them the most accurate information possible.”
Dr. Eduardo Tizzano
Director of the Department of Clinical and Molecular Genetics, Vall d’Hebron Hospital.
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Improved supportive care has reduced early mortality in SMA type 1, but nearly half of surviving infants are dependent on non-invasive ventilation.8,9
Creating patient confidence in the multidisciplinary team is one factor in achieving improved patient outcomes.10
The management of treatment expectations can be facilitated with the use of a promise card, filled in by the patient. As lack of SMN protein is the cause of SMA, the primary treatment goal is to increase SMN protein in the patients.6
Learn more about Biogen’s offering for SMA in Children here
The characters shown are real patients and the required consent to use their stories has been obtained from the patients and families. Photographs are for illustrative purposes only.
References
1. Sugarman EA et al. Eur J Hum Genet. 2012;20(1):27–32.
7. Lin CW, et al. Delay in Diagnosis of Spinal Muscular Atrophy: A Systematic Literature Review. Pediatr Neurol. 2015;53(4):293-300.
8. Mercuri E, Finkel RS, Muntoni F, et al. Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord. 2018;28(2):103-115.
9. Finkel RS, Mercuri E, Meyer OH, et al. Diagnosis and management of spinal muscular atrophy: Part 2: Pulmonary and acute care; medications, supplements and immunizations; other organ systems; and ethics. Neuromuscul Disord. 2018;28(3):197-207.
10. Nunlist et al. Fam Pract Manag. 2016;23(6):21–24.
