Human fetal brain tissue from elective terminations of pregnancy (12–19 PCW) was provided by the Human Developmental Biology Resource (HDBR) (http://www.hdbr.org). Fetal age was determined by the HDBR through foot length and knee-to-heel length measurements. Fetal sex was determined by karyotyping and confirmed in this study through male-specific expression of genes on the Y-chromosome and heterozygosity for X-chromosome markers in females. No other phenotypic or demographic information was available. Brain tissue was obtained frozen and had not been dissected into regions. Total RNA was extracted from half of the available brain tissue from each fetus using Tri-Reagent (Thermo Fisher Scientific), while the other half of each sample was processed for genomic DNA using standard phenol-chloroform extraction.
