Emerging role of miRNA in attention deficit hyperactivity disorder: a systematic review

Attention deficit hyperactivity disorder (ADHD) is a neuropsychiatric disorder whose aetiology still remains elusive. Nevertheless, evidence supports a high genetic contribution that interacts with environmental factors, also known to modulate epigenetic processes. These epigenetic modulators are a class of non-coding RNAs, microRNAs (miRNAs), known as post-transcriptional regulators, which have emerged as prospective players in neuropsychiatric disorders since they play a role in brain development, synapse formation, and the fine-tuning of genes underlying synaptic and memory formation. Here, we review the current literature following a systematic search up until August 2016. The keywords used were "ADHD", "attention deficit hyperactivity disorder", "attention hyperactivity" in combination with "miRNA" or "microRNA". A total of 9 studies out of 34 met inclusion criteria. The results provide preliminary information, shedding light on two important aspects. First, it depicts that miRNAs modulate expression of genes (BDNF, DAT1, HTR2C, HTR1B, SNAP-25) linked to ADHD aetiology. Dysregulation of miRNAs affects regulatory mechanisms of aforementioned genes, which may affect neurodevelopmental processes leading to alterations. Secondly, altered peripheral miRNA levels are observed in both ADHD animal model and humans, suggesting a notion of utilizing circulatory miRNA in disease diagnosis. Therefore, deciphering the role of miRNAs in ADHD seems a promising step in understanding its aetiology.