With regards to CHRM1 levels in people with schizophrenia, current data suggests that the lower levels of CHRM1 are not associated with a gene variant (Scarr et al., 2009) but could be due to changes in gene methylation (Scarr et al., 2013a) which is affected by environmental factors (Smigielski et al., 2020). This evidence concerns the gene CHRM1 and schizophrenia.