Liquidity of gene co-expression trajectories across the lifespan highlights delayed maturation and the perinatal GABA switch in schizophrenia risk
Schizophrenia genetic and environmental risk factors play out largely in early life, biasing development toward a pathogenic trajectory that becomes clinically apparent in early adulthood, when the disorder typically onsets. Here, we convert snapshots of gene expression in postmortem brain at a moment in time into a dynamic lifetime series employing the "liquidity" metric, a novel tool to track the evolution of networks across time from a multi-systemic perspective. The landscape of normal prefrontal cortical development becomes increasingly "liquid" during the first two decades of post-natal life, with sharp discontinuities in known critical periods such as birth and adolescence. Neurotypical individuals free of apparent neuropathology with relatively elevated polygenic risk scores for schizophrenia exhibit a generalized delay in the dynamics of liquidity across these trajectories compared to below-average-risk individuals. Impacted biological processes strongly converge on delayed GABA-A receptor functional maturation, involved in establishing Excitatory/Inhibitory balance in brain during early development. Similar to patients with schizophrenia, neurotypical high-risk individuals show an increased expression ratio between the genes SLC12A2 (protein NKCC1) and SLC12A5 (protein KCC2) relative to low-risk, involved in the control of the equilibrium potential of chloride ions that regulates GABA-A function. These results provide evidence that genetic risk for schizophrenia is associated with a delayed maturational profile and delayed maturation of GABAergic signaling without detectable neuropathology and well before the age of clinical onset. Interestingly, the same effect is not observed in the hippocampus and is not observed with genetic risk for other neuropsychiatric and immune conditions. The dynamics of maturation of GABA-A signaling in the dorsolateral prefrontal cortex emerge as an early contributor to translating genetic risk into an altered developmental trajectory associated with schizophrenia.