Incomplete penetrance of CRX gene for autosomal dominant form of cone-rod dystrophy.

Purpose: Cone-rod dystrophy (CRD) is an inherited retinal dystrophy that is transmitted via different modes of inheritance. Mutations in more than 30 genes have been identified to cause the disease. We aimed to investigate the genetic agents of two unrelated cone-rod dystrophy affected Iranian families with autosomal recessive inheritance patterns. Methods: Whole-exome sequencing (WES) was performed for identification of the disease-causing mutations in the probands of both families. The candidate mutations were further confirmed by Sanger sequencing. Samples from five available members of each family were then sequenced for the mutations present in the probands. Comprehensive ocular examinations for all members of the families carrying the mutations were completed by ophthalmologists. Results: We identified a novel premature stop codon c.310C>T in CRX gene in heterozygote form in two symptomatic and two non-symptomatic members of one family (family-A), and a known CRX mutation c.122G>A in homozygote form in another (family B). c.122G>A has been reported to cause late-onset autosomal dominant form of the disease in previous studies. However, the middle-aged heterozygous carriers of the mutation in this family showed normal phenotype. Conclusion: The CRX gene has been previously linked to the autosomal dominant form of cone-rod dystrophy. We report incomplete penetrance of CRX gene for autosomal dominant form of the disease. Incomplete penetrance of the mutations may be partly caused by the influence of other genes in the complex genetic network underlying retinal regulation.

Support for "Disease-Only" Genotypes and Excess of Homozygosity at the CYTH4 Primate-Specific GTTT-Repeat in Schizophrenia.

OBJECTIVE: 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. METHODS: 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. RESULTS: 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 exact <0.007). The frequency of the 11-repeat allele was estimated at 0.02 and 0.006 in the SCZ patients and controls, respectively (Mid p exact <0.006). CONCLUSION: 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.

Association of ß-Secretase Functional Polymorphism with Risk of Schizophrenia.

AIM: The NRG1-ERBB4 neurotransmitter signaling pathway plays a key role in the pathogenesis of schizophrenia (SZ). The intronic single-nucleotide polymorphism rs707284 in ERBB4 links to PI3K-AKT suppression in SZ. Another protein indirectly affecting NRG1-ERBB4 signaling is ß-secretase, which is encoded by the BACE1 gene, and activates NRG1 by proteolytic cleavage. In this study, we aimed to investigate the association of ERBB4 rs707284 and BACE1 rs490460 with the risk of SZ in an Iranian population. SUBJECTS AND METHODS: A total of 973 subjects, including 480 SZ patients and 493 healthy controls, matched by ethnicity, age, and gender, were recruited in a case-control study. Genomic DNA was extracted from peripheral blood of all subjects and genotyping of rs707284 and rs490460 was performed using polymerase chain reaction (PCR)-restriction fragment length polymorphism and tetra-primer amplification refractory mutation system (tetra-ARMS) PCR genotyping assays, respectively. RESULTS: A significant association was observed between the rs490460 T allele and SZ (p = 0.0002, odds ratio 0.69, 95% confidence interval 0.57-0.84). There was no association between the risk of SZ and rs707284. CONCLUSION: Our data indicate that rs490460 is associated with the risk of SZ. In silico analysis indicates that rs490460 may be a potential splicing site, which affects protein structure. Replication studies are needed to confirm our data.

A genetic variant in miRNA binding site of glutamate receptor 4, metabotropic (GRM4) is associated with increased risk of major depressive disorder.

BACKGROUND: Glutamate receptor 4, metabotropic (GRM4) expression is increased in the brain of patients with depression. The poorly conserved miR-1202 is downregulated in depression and is negatively correlated with GRM4. A variation located at the 3' UTR of the GRM4 gene may influence the interaction between miR-1202 and GRM4. The aim of this study was to determine the possible association between GRM4 3' UTR variant (rs2229901) and major depressive disorder (MDD). METHODS: A total of 500 subjects comprising 250 patients with MDD and 250 healthy controls were included in our study. The single nucleotide polymorphism rs2229901 was genotyped using PCR-RFLP method. Allele and genotype frequencies were compared between the two groups using chi-square test and logistic regression models. The impact of rs2229901 on GRM4/miR-1202 hybrid stability and local GRM4-3' UTR secondary structure were assessed using RNAsnp program. RESULTS: Genotype and allele frequency of rs2229901were significantly different in patients with MDD comparing to the control group (p=0.018 and p=0.007, respectively). The G-allele was more prevalent among patients with MDD. The rs2229901 variant was predicted to be structure-disruptive. LIMITATIONS: The relatively small sample size and lack of functional experiments are the major limitations of this study. CONCLUSION: Our results suggest that rs2229901 is associated with MDD risk. This variant probably impacts the interaction between GRM4 and miR-1202. Functional studies are needed to clarify the possible mechanisms by which rs2229901 influences MDD risk.

The analysis of association between SNCA, HUSEYO and CSMD1 gene variants and Parkinson's disease in Iranian population.

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.

c.376G>A mutation in WFS1 gene causes Wolfram syndrome without deafness.

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.

A genetic variant in CAMKK2 gene is possibly associated with increased risk of bipolar disorder.

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.