No abstract

PRKACB (Protein Kinase CAMP-Activated Catalytic Subunit Beta) is predominantly expressed in the brain, and regulation of this gene links to neuroprotective effects against tau and Aβ-induced toxicity. Here we studied a (GCC)-repeat spanning the core promoter and 5′ UTR of this gene in 300 human subjects, consisting of late-onset neurocognitive disorder (NCD) (N = 150) and controls (N = 150). We also implemented several models to study the impact of this repeat on the three-dimensional (3D) structure of DNA. While the PRKACB (GCC)-repeat was strictly monomorphic at 7-repeats, we detected two 7/8 genotypes only in the NCD group. In all examined models, the (GCC)7 and its periodicals had the least range of divergence variation on the 3D structure of DNA in comparison to the 8-repeat periodicals and several hypothetical repeat lengths. A similar inert effect on the 3D structure was not detected in other classes of short tandem repeats (STRs) such as GA and CA repeats. In conclusion, we report monomorphism of a long (GCC)-repeat in the PRKACB gene in human, its inert effect on DNA structure, and enriched divergence in late-onset NCD. This is the first indication of natural selection for a monomorphic (GCC)-repeat, which probably evolved to function as an “epigenetic knob”, without changing the regional DNA structure.

The rs3129882, a noncoding variant in HLA-DR, was found to be associated with Parkinson's disease (PD) using several genome-wide association studies. The aim of this replication study was to explore the relationship between this variant and PD in Iranian population. Genomic DNA was extracted from peripheral blood samples, and the rs3129882 SNP was genotyped using a PCR-RFLP method in 520 PD patients and 520 healthy Iranian controls. Significant differences were found in allele frequencies between patients and controls (χ(2) = 4.64, P = 0.031). Under additive and dominant models, the association of the SNP with PD risk is significant, where the A allele was observed to be protective. The results suggest that rs3129882 polymorphism may be a risk factor for PD in Iranian. This is the first study reporting such an association in this population. More replication studies are needed to confirm this data.

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 and genotypes that deviate from those alleles are underappreciated features, which may have deep evolutionary and pathological consequences.

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.