Targeted mutational sequencing of HARs in an autism cohort revealed a variant in a HAR at the CUX1 locus that was found to increase enhancer activity, leading to increased spine density with more stable synapses.146 This combination of comparative and human genetics is a powerful approach and provides compelling evidence that CUX1 and its associated HAR may be important in the evolutionary differences in neuronal morphology. This evidence concerns the gene HARS1 and autism.