Application of the Short Tandem Repeat Marker (D21S11) in the Molecular Diagnosis of Down Syndrome in Libya

Background: Down syndrome (DS) is the most common genetic anomaly linked to varying degrees of intellectual disability, distinct physical traits and health issues. PCR-based DNA diagnostic method is sensitive, robust and the most efficient for trisomy 21 diagnosis. Aim: This study aimed to demonstrate the sensitivity of DNA diagnosis of DS using the short tandem repeat (STR) marker D21S11. Methods: This study was conducted in Tripoli, Libya. Blood samples were collected from 55 individuals, of which 50 were successfully amplified and included in the analysis. In addition, 102 healthy controls were included to assess the sensitivity of the D21S11 marker for detecting chromosome 21 (Ch21) nondisjunction (NDJ). The GlobalFiler™ IQC PCR Amplification kit and a 3500 Genetic Analyzer were used to detect trisomy 21 by the D21S11 locus on Ch21. Results: Diagnosis of Ch21 trisomy was achieved in all 50 successfully amplified samples (100%), including one mosaic case. Of the 50 cases, 26 (52%) showed a diallelic pattern, 21 cases (42%) showed a triallelic pattern and 3 cases (6%) showed a monoallelic pattern. Conclusion: This study successfully diagnosed, for the first time, Ch21 NDJ in individuals with DS cases, including one mosaic case, using the STR marker (D21S11) and genetic analyzer in the Libyan population. This method may be applied to prenatal and postnatal diagnosis as well as preimplantation genetic diagnosis, as it is rapid, simple, accurate, and requires only a small amount of biological material compared with conventional cytogenetic analyses.