Natural selection at the RASGEF1C (GGC) repeat in human and divergent genotypes in late-onset neurocognitive disorder.
Abstract Expression dysregulation of the neuron-specific gene, RASGEF1C (RasGEF Domain Family Member 1C), occurs in late-onset neurocognitive disorders (NCDs), such as Alzheimer’s disease. This gene contains a (GGC)13, spanning its core promoter and 5′ untranslated region (RASGEF1C-201 ENST00000361132.9). Here we sequenced the (GGC)-repeat in a sample of human subjects (N=269), consisting of late-onset NCDs (N=115) and controls (N=154). We also studied the status of this STR across various primate and non-primate species based on Ensembl 103. The 6-repeat allele was the predominant allele in the controls (frequency=0.85) and NCD patients (frequency=0.78). The NCD genotype compartment consisted of an excess of genotypes that lacked the 6-repeat (divergent genotypes) (Mid-P exact=0.004). A number of those genotypes were not detected in the control group (Mid-P exact=0.007). The RASGEF1C (GGC)-repeat expanded beyond 2-repeats specifically in primates, and was at maximum length in human. We conclude that there is natural selection for the 6-repeat allele of the RASGEF1C (GGC)-repeat in human, and significant divergence from that allele in late-onset NCDs. STR alleles that are predominantly abundant in human and genotypes that deviate from those alleles are underappreciated features, which may have deep evolutionary and pathological consequences in human.