Microsatellites (MS) are non-coding regions of DNA that are found throughout the genome, characterized by the repetition of specific sequence motifs in varying lengths. Every individual carries two copies (alleles) of each microsatellite in their nucleated cells, which can differ in length depending on whether they originate from the mother or father. The pattern of microsatellite lengths across multiple loci constitutes an individual’s genetic fingerprint, which is unique for every person except identical twins. By analysing several microsatellites simultaneously, a unique DNA profile can be created for an individual within a population group, with an accuracy exceeding 99.999999%. Comparing microsatellite patterns between individuals, combined with established biostatistical methods, allows for highly reliable determination or exclusion of biological relationships. Microsatellite analysis is also widely applied in forensics and to rule out contamination in prenatal diagnostics.

Microsatellites also play an important role in various tumour diseases. Their repetitive structure makes them prone to a high mutation rate, which can result in microsatellite instability (MSI) in tumours. MSI refers to the presence of microsatellites with altered lengths that are not found in the corresponding germline DNA, typically caused by defects in the DNA mismatch repair (MMR) system. Variants in MMR genes can lead to faulty DNA replication during cell division in tumour tissues, producing variable microsatellite lengths detectable as MSI. Determining and detecting MSI is not only important for diagnosing and classifying tumours but also provides valuable prognostic and therapeutic insights.