1 In Vitro Diagnostic use (IVD): only in the countries specified on the title page of the instructions for use. In all other countries, this product is for Research Use Only (RUO).
2 In people of African descent, the percentage of SMA patients with a homozygous exon 7 deletion may be lower (Labrum et al. 2007). This assay does not detect other causes of SMA such as pathogenic point mutations.
Spinal muscular atrophy (SMA) is a severe, recessive, neuromuscular disease for which treatment options have recently become available. SMA is caused by a complete absence of functional copies of the SMN1
gene. In most populations, homozygous absence of the exon 7 DNA sequence of the SMN1
gene is observed in 95-98% of SMA patients. In most remaining cases, point mutations or partial deletions in the SMN1
gene are the cause of disease. For more information see Appendix 1: Background Information in the instructions for use.
In the SALSA MC002 SMA Newborn Screen PCR, amplification of exon 7 of the SMN1
gene and the closely related SMN2
gene is performed, followed by fluorescent probe binding to the amplicons and generation of a melt curve (Figure 1, Strunk et al. 2019). Fluorescence is only measured during melt curve generation.
Absence of the SMN1
-specific melt peak at 63°C is indicative of the absence of the SMN1
exon 7 DNA sequence. The presence of an SMN1
(63°C) and/or SMN2
(56°C) specific melt peak and an absent or low signal for the Q (quantity)-fragment specific melt peak (49°C) indicates successful assay performance and the use of sufficient sample DNA. The assay uses a crude DNA extract prepared from a 1.5 mm or 3.2 mm punch of a DBS card or purified DNA from peripheral blood. More information on the assay can be found in Appendix 2: SALSA MC002 SMA Newborn Screen in the instructions for use.
Figure 1. Summary of assay steps. (A) The exon 7 regions of SMN1 and SMN2 are amplified with a single set of primers, with one primer in excess. (B) A fluorescently-labelled probe binds to the amplicons. (C) The resulting melt curve indicates SMN1 and SMN2 sequence presence and DNA quantity.
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