Table 5.

A summary of studies aimed to detect silent carriers.

Author	Methods	Result
Luo et al. (2014) [30]	Microsatellite analysis identified haplotype blocks and next-generation sequencing identified specific SNPs associated with the 2+0 genotype in those with Ashkenazi Jewish heritage.	Identified g.27134T>G in intron 7 and g.27706_27707delAT in exon 8 as polymorphisms associated with 2+0 carrier status. This also had predictive value in those of an African American, Asian, Hispanic, and Caucasian background.
Alias et al. (2018) [31]	Examined g.27134T>G and g.27706_27707delAT in a Spanish population	It was found that the presence of the SNPs increased or reduced the residual carrier risk in this population.
PCR-Based Technologies
Vidal-Folch et al. (2018) [32]	Used digital droplet PCR to simultaneously screen for SMN1 and SMN2 copy numbers as well as the g.27134T>G SNP.	Allowed for accurate screening of carriers without requiring standard curves. Interassay imprecision was <7.1% CV and interassay imprecision was <6.0% CV. Testing was 100% specific and sensitive in SMA.
Azad et al. (2020) [33]	Custom SNP-specific assay using TaqMan genotyping technology to determine CNV of SMN1, SMN2 and presence of g.27134T>G SNP	Results are 100% concordant with standard PCR in 21 pilot samples. Good reproducibility with a 1–4% CV for all genotypes.
Next-Generation Sequencing Technologies
Feng et al. (2017) [34]	Paralogous gene copy-number analysis by ratio and sum to detect SMN1, SMN2 copy numbers, and g.27134T>G SNP on short-read next-generation sequence	Results are 100% sensitive and 99.6% specific to detect 1 copy of SMN1, and 100% concordant detection of g.27134T>G SNP compared to RFLP assay. Carrier detection rates increased according to ethnic heritage; African American (70.5% to 90.3%), Ashkenazi Jewish (90.5% to 92.8%), Asian (93.3% to 93.6%), Caucasian (94.8% to 95%), and Hispanic (90% to 92.6%)
Ceylan et al. (2020) [35]	Used CODE-SEQ technology; an NGS assay of 18 pairs of coded oligonucleotides coupled with a unique probe to target SMA-related loci and reference regions	Results show 100% correlation with the MLPA results in all 80 samples tested for exon 7 SMN1 CN. Unable to test the accuracy in the detection of the g.27134T>G SNP as none were present in the sample.
Chen et al. (2020) [36]	Analysed read depth and used eight reference genome differences to identify copy number of SMN1 and SMN2 as well as g.27134T>G SNP.	Accuracy of 99.8% and 99.7% for SMN1 and SMN2 CN compared to qPCR and MLPA, precision of 100% for both SMA and 1+0 carrier status. Carrier detection rates increased with SNP by 21.3% in those with African heritage and 2% at most for all other heritages.
Li et al. (2022) [28]	Utilised long-range PCR and third-generation sequencing of full-length and downstream regions of SMN1 and SMN2.	Improved detection rates of SMA carriers in a Chinese population from 91% to 98%, including three SMN1 intragenic mutations and an in-frame mutation to SMN2.