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Prenatal onset spinal muscular atrophy
M J MacLeod1, J E Taylor, P W Lunt
1Department of Paediatric Neurology, Guy's Hospital, St Thomas Street, London, SE1 9RT, UK.
Insights
Severe spinal muscular atrophy (SMA) type I is linked to specific gene mutations. Reduced copy number of the centromeric survival motor neuron gene (SMNc) may influence disease severity in SMA patients.
Area of Science:
- Genetics
- Neurology
- Molecular Biology
Background:
- Spinal muscular atrophy (SMA) type I is a severe genetic neuromuscular disorder.
- Patients often present with significant weakness at birth and reduced fetal movements.
- Understanding the genotype-phenotype correlation is crucial for diagnosis and prognosis.
Observation:
- Five patients with severe SMA type I were analyzed.
- Clinical, electrophysiological, and histopathological features confirmed the diagnosis.
- Molecular diagnosis involved polymerase chain reaction and gene-dosage assays.
Findings:
- All patients lacked the telomeric survival motor neuron gene (SMNt).
- The centromeric survival motor neuron gene (SMNc) was present but in reduced copy number compared to controls.
- Reduced SMNc copy number may be a key factor in determining SMA type I severity.
Implications:
- SMA should be considered in the differential diagnosis of reduced fetal movements.
- Molecular genetic findings can clarify the clinical classification of SMA.
- This research highlights the importance of gene dosage in SMA pathogenesis.
Abstract:
Five patients with severe spinal muscular atrophy (SMA) type I, all of whom presented with reduced fetal movements in utero, severe weakness at birth, and short survival time were assessed to attempt to determine whether their phenotype could be explained by their genotype. The diagnosis was confirmed by clinical, electrophysiological and histopathological features. Polymerase chain reaction assays were used to define the molecular diagnosis. A gene-dosage assay was used to assess the quantity of centromeric survival motor neuron gene (SMNc) present. In all cases the telomeric survival motor neuron gene (SMNt) was absent. The SMNc gene was present but in reduced copy number compared with a control group of children with less severe type I SMA, so may be important in determining severity. In the differential diagnosis of reduced fetal movements, SMA should be considered. The clinical classification may in future be clarified by molecular genetic findings.