*3.8. Stem Loops*

The median number of 5′UTR stem loops in ABCA genes was determined to be 3; the mode was 2. The minimum was 0 (*ABCA13*) and maximum 6 (*ABCA1* and *ABCA12*). Stem loops (hairpins) are the most frequent secondary structures, which naturally fold along single-stranded RNA molecules [48]. The strength of their effect on translation is dependent on the location within 5′UTRs as well as their stability; however, they mainly inhibit this process in eukaryotic cells [17]. The mechanism of stem loop influence on translation has been examined in detail in many studies [49,50] and the prevalence of stem loops in 5′UTRs is generally thought to be high [51,52]. However, the precise stem loop incidence in specific gene groups has not been calculated yet and we were not able to compare our results to the results of others. Our work, therefore, brings largely new information on this topic.
