Search

The role of short tandem repeats (STRs) in the control of gene expression among species is being increasingly understood following the identification of several instances in which certain STRs occur identically, or expand differentially, in primates versus nonprimates. These STRs may regulate genes that participate in characteristics that are associated with the divergence of primates from sibling orders (e.g., brain higher order functions). The CYTH4 gene contains the longest tetranucleotide STR in its core promoter, at 7-repeats, and links to the evolution of human and nonhuman primates. Allele and genotype distribution of this STR were studied in patients affected by schizophrenia (SCZ) and controls.High-resolution data were obtained on the allele and genotype distribution of the CYTH4 STR and a novel C T single-nucleotide polymorphism (SNP) at its immediate upstream sequence in 255 patients with SCZ and 249 controls. Each sample was sequenced twice using the fluorescent dye termination method.Novel alleles were detected at the long extreme of the GTTT-repeat, at 10- and 11-repeats, in the SCZ cases and controls. Excess of homozygosity was observed for the entire range of alleles across the GTTT-repeat and the C T SNP in the SCZ patients in comparison with the controls (Yates corrected p 0.011). Three genotypes consisting of the 11-repeat allele (i.e., 11/11, 10/11, and 7/11) were detected only in the SCZ patients (i.e., disease-only genotypes), and contributed to 2.3% of the SCZ genotypes (Mid p exact0.007). The frequency of the 11-repeat allele was estimated at 0.02 and 0.006 in the SCZ patients and controls, respectively (Mid p exact0.006).This indicates that STR genotypes that are absent in the control group may be risk factors for SCZ. Future studies are warranted to test the significance of our findings.

Neurological disorders include a wide variety of mostly multifactorial diseases related to the development, survival, and function of the neuron cells. Single-nucleotide polymorphisms (SNPs) have been extensively studied in neurological disorders, and in a number of instances have been reproducibly linked to disease as risk factors. The RIT2 gene has been recently shown to be associated with a number of neurological disorders, such as Parkinson's disease (PD) and autism. In the study reported here, we investigated the association of the rs12456492 and rs16976358 SNPs of the RIT2 gene with PD, essential tremor (ET), autism, schizophrenia (SCZ), and bipolar disorder (BPD; total of 2290 patients), and 1000 controls, by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Significant association was observed between rs12456492 and two disorders, PD and ET, whereas rs16976358 was found to be associated with autism, SCZ, and BPD. Our findings are indicative of differential association between the RIT2 SNPs and different neurological disorders.

DNA variations in the fibroblast growth factor 20 gene have been reported to be associated with Parkinson's disease (PD). The rs12720208, a functional SNP located in the 3'UTR region of the gene, was reported as a risk factor for PD. A number of studies, which tried to replicate the result in different populations, failed to detect any associations. In this study, we genotyped rs2720208 SNP in 520 PD patients and 520 healthy controls both from Iran. Significant differences were found in allele and genotype frequencies between patients and controls (p

In this study, the role of known Parkinson’s disease (PD) genes was examined in families with autosomal recessive (AR) parkinsonism to assist with the differential diagnosis of PD. Some families without mutations in known genes were also subject to whole genome sequencing with the objective to identify novel parkinsonism-related genes. Families were selected from 4000 clinical files of patients with PD or parkinsonism. AR inheritance pattern, consanguinity, and a minimum of two affected individuals per family were used as inclusion criteria. For disease gene/mutation identification, multiplex ligation-dependent probe amplification, quantitative PCR, linkage, and Sanger and whole genome sequencing assays were carried out. A total of 116 patients (50 families) were examined. Fifty-four patients (46.55%; 22 families) were found to carry pathogenic mutations in known genes while a novel gene, not previously associated with parkinsonism, was found mutated in a single family (2 patients). Pathogenic mutations, including missense, nonsense, frameshift, and exon rearrangements, were found in Parkin, PINK1, DJ-1, SYNJ1, and VAC14 genes. In conclusion, variable phenotypic expressivity was seen across all families.

Wolfram syndrome is one of the rare autosomal recessive, progressive, neurodegenerative disorders, characterized by diabetes mellitus and optic atrophy. Several other features are observed in patients including deafness, ataxia, and peripheral neuropathy. A gene called WFS1 is identified on chromosome 4p, responsible for Wolfram syndrome. We investigated a family consisted of parents and 8 children, which 5 of them have been diagnosed for Wolfram syndrome. WFS1 gene in all family members was sequenced for causative mutations. A mutation (c.376G>A, p.A126T) was found in all affected members in homozygous state and in both parents in heterozygous state. The bioinformatics analysis showed the deleterious effects of this nucleotide change on the structure and function of the protein product. As all of the patients in the family showed the homozygote mutation, and parents were both heterozygote, this mutation is probably the cause of the disease. We identified this mutation in homozygous state for the first time as Wolfram syndrome causation. We also showed that this mutation probably doesn't cause deafness in affected individuals.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder. Both genetic and environmental factors are involved in the etiology of the disease. Many studies have revealed the susceptibility genes and variations for PD which need further confirmation. Here we evaluated the association of variations in SNCA, HUSEYO and CSMD1 genes with PD. A case-control study was conducted with 489 PD patients and 489 healthy controls. DNA was extracted from peripheral blood of all subjects and rs356220 and rs11931074 in SNCA, rs2338971 in HUSEYO and rs12681349 in CSMD1 were genotyped using PCR-RFLP method. The genotypes and allele frequencies were significantly different between case and control groups for rs356220, rs11931074 and rs2338971 but not for rs12681349. We provided further evidence that rs356220 is associated with increased risk of PD supporting previous studies in Caucasian-based and Japanese populations. The association of rs11931074 with decreased risk of PD was also significant. This study revealed the first evidence of the association of rs2338971 with increased risk of PD in the Iranian population. Nevertheless, these findings need further validation via more replication studies.

A recent large-scale study have reported that rs1063843, a single nucleotide polymorphism located in the CAMKK2 gene is highly associated with schizophrenia in European and Han Chinese populations. Increasing evidences show that schizophrenia and bipolar disorder have some common genetic variance. Here, we evaluated the association of this variant with schizophrenia and bipolar disorder in Iranian population. Genomic DNA was extracted from peripheral blood of 500 schizophrenic patients, 500 bipolar patients and 500 normal controls and all were genotyped for the rs1063843 using a PCR-RFLP method. The allele frequency of rs1063843 was significantly different in both schizophrenia and bipolar patients comparing to control group. For the first time, we showed that rs1063843 is highly associated with bipolar disorder, although more replication studies are needed to confirm our findings. Our results also support the findings of previous studies suggesting a significant association between rs1063843 and schizophrenia.

Primate-specific genes and regulatory mechanisms could provide insight into human brain functioning and disease. In a genome-scale analysis of the entire protein-coding genes listed in the GeneCards database, we have recently reported human genes that contain “exceptionally long” short tandem repeats (STRs) in their core promoter, which may be of adaptive/selective evolutionary advantage in this species. The longest tetra-nucleotide repeat identified in a human gene core promoter belongs to the CYTH4 gene. This GTTT-repeat is specific to Hominidae and Old World monkeys, and the shortest allele of this repeat, (GTTT)6, is linked with neural dysfunction and type I bipolar disorder in human. In the present study, we sought a possibly broader role for the CYTH4 gene core promoter GTTT-repeat in neural functioning and investigated its allelic distribution in a total of 949 human subjects, consisting of two neurodegenerative disorders, multiple sclerosis (MS) (n = 272) and Alzheimer’s disease (AD) (n = 257), and controls (n = 420). The range of the alleles of this GTTT-repeat in the human sample studied was between 6- and 9-repeats. The shortest allele, (GTTT)6, was significantly in excess in the MS and AD patients in comparison with the controls (p < 0.004). The 6/6, 6/7, and 7/7 genotypes were in excess in the MS and AD patients, whereas the overall frequency of all other genotypes (consisting of at least one longer allele, i.e., 8- or 9-repeat) was higher in the controls (p < 0.005), indicating a dominant and protective effect for the longer alleles against neurodegeneration. This is the first indication of the involvement of a primate-specific STR in neurodegeneration in humans. We propose an adaptive evolutionary role for the expansion of the CYTH4 gene core promoter GTTT-repeat in the human brain, which is supported by a link between the shortest allele of this repeat with neuropsychiatric disorders.