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Screening for two SMN1 variants associated with spinal muscular atrophy carriers of 2+0 genotype
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Spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality and is characterized by motor neuron loss in the spinal cord and lower brainstem, muscle weakness, and atrophy. The homozygous deletion of the SMN1 gene, the fully functional orthologue, is the most prevalent genetic cause of SMA. The SMN2 gene, which shares a high sequence homology with SMN1, primarily produces unstable, truncated messenger RNA (mRNA), and consequently a limited amount of fully functional protein. SMN2 gene copy number serves as a valuable prognostic biomarker for assessing the clinical severity of SMA, albeit not absolute. Heterozygous carriers of SMA typically possess one SMN1 copy on
one allele (1+0 genotype). Some carriers exhibit SMN1 deficiency on one chromosome but have two SMN1 copies in cis on the other (2+0 genotype), rendering them "silent" carriers, indistinguishable from noncarrier individuals (1+1 genotype) using current quantitative techniques. Notably, the SMN1 variants c.*3+80T>G and c.*211_*212del were associated with 2+0 carriers in Ashkenazi Jews and Spanish populations. In this study, we employ a suitable screening method to identify these variants, and evaluate their relationship with 2+0 carrier status within the Portuguese population. As the CGM-ULSSA serves as a national reference laboratory for SMA genetic diagnosis, implementing cost-effective screening methods for these variants could prove instrumental in enhancing genetic counselling.
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Survival of Motor Neuron 1 Protein / genetics Muscular Atrophy Spinal / diagnosis Spinal / genetics Genetic Carrier Screening Genetic Counselling