A massively parallel reporter assay of MECP2 cis-regulatory elements reveals genetic candidates for male-biased autism

One hypothesis is that hypomorphic variants in X-linked genes—genes where loss-of-function alleles cause syndromic neurodevelopmental disorders (NDDs) predominantly in females—produce milder, non-syndromic phenotypes in hemizygous males. We tested this by investigating cis-regulatory elements (CREs) of MECP2, a dosage-sensitive X-linked gene.

Using a massively parallel reporter assay in human neurons, we mapped transcription factor binding sites within MECP2 CREs and tested autism-associated variants for functional impact. We identified two noncoding variants that change CRE activity, each with a male-biased phenotype. One of these, a promoter variant, disrupts NFY binding and reduces MECP2 expression by ~30%, a magnitude that produces autism-like phenotypes in mice.