Circulating Organ-enriched microRNAs as biomarkers of Rett Syndrome

SUMMARY Rett syndrome (RTT) is a rare X-linked neurodevelopmental disorder caused by mutations in the MECP2 gene. The disease affects females almost exclusively, since male fetuses with a MECP2 mutation usually die before birth. Affected females appear normal at birth; disease onset is typically evident by 6-18 months and is characterized by neurological regression, motor stereotypies, irregular breathing, and other handicaps. Clinical severity appears to depend on multiple factors, including the type of MECP2 mutation, skewing of the X- inactivation and likely genetic modifiers of MECP2. Although diagnostic MECP2 genetic testing is available for RTT, peripheral biomarkers of RTT, including minimally invasive, blood-based indicators of disease severity and progression, are lacking. DiamiR, a molecular diagnostics company, has developed proprietary platform technology for early detection and monitoring of pathophysiological processes based on analysis of circulating organ-enriched, including brain-enriched, microRNAs (miRNAs) in plasma. Studies conducted to date at the company resulted in identification of promising miRNA biomarker candidates for neurodegenerative and other diseases, and here we propose extending the use of our technology to establish miRNA biomarkers of RTT. Loss of MECP2 results in synaptic dysfunction and marked dysregulation of miRNAs in the brain. We hypothesize that circulating miRNAs enriched in different brain regions, present in synapses/neurites, and detectable in plasma can detect pathophysiological processes associated with RTT development. In addition, analysis of levels of miRNAs enriched in liver, lung and muscle can be reflective of RTT associated changes in these tissues. An “miRNA pair” approach is used for data normalization, and a biomarker candidate is comprised of a ratio of two miRNAs. Two-three miRNA pairs are combined into a miRNA classifier for higher accuracy. Preliminary studies performed with four murine models and human patients identified miRNA pairs and classifiers differentiating both RTT mouse models from wild-type mice and RTT patients from age-matched control (AMC); certain miRNA pairs were common to mice and humans, indicating the similarity between the underlying pathological processes. The current study will be performed using plasma samples collected at the Rett Center at Montefiore Medical Center. Specific aims include: (1) assessing the feasibility of differentiating RTT from AMC by plasma levels of 38 pre-selected circulating miRNAs enriched in organs/tissues affected by RTT (brain, liver, lung, muscle) (60 RTT/60 AMC); and (2) evaluating the potential of circulating miRNAs for predicting disease severity and monitoring disease progression by analysis of plasma levels of the previously studied 19 miRNAs in the longitudinal set of samples collected 3 years later from the same study participants (30 RTT/30 AMC). SBIR Phase II will involve larger clinical studies to validate miRNA biomarker candidates. The assay will be initially developed as a clinical trial assay, and, upon accumulation of clinical data, as in vitro diagnostics.NARRATIVE Rett syndrome (RTT) is a rare (1 in every 10,000-15,000 live-born female babies) neurodevelopmental disorder caused by mutations in the MECP2 gene that is characterized by neurological regression, microcephaly, motor stereotypies, irregular breathing, and other handicaps. Although diagnostic MECP2 genetic testing is available for RTT, biomarkers of RTT, including minimally invasive, blood-based indicators of disease severity and progression, are lacking. In this SBIR, DiamiR applies its proprietary platform technology based on targeted analysis of organ-enriched microRNAs in plasma to develop a sensitive assay for RTT staging/prognosis and disease and treatment monitoring.