High prevalence of multilocus pathogenic variation in neurodevelopmental disorders in the Turkish population.

Neurodevelopmental disorders (NDDs) are clinically and genetically heterogenous; many such disorders are secondary to perturbation in brain development and/or function. The prevalence of NDDs is > 3%, resulting in significant sociocultural and economic challenges to society. With recent advances in family-based genomics, rare-variant analyses, and further exploration of the Clan Genomics hypothesis, there has been a logarithmic explosion in neurogenetic "disease-associated genes" molecular etiology and biology of NDDs; however, the majority of NDDs remain molecularly undiagnosed. We applied genome-wide screening technologies, including exome sequencing (ES) and whole-genome sequencing (WGS), to identify the molecular etiology of 234 newly enrolled subjects and 20 previously unsolved Turkish NDD families. In 176 of the 234 studied families (75.2%), a plausible and genetically parsimonious molecular etiology was identified. Out of 176 solved families, deleterious variants were identified in 218 distinct genes, further documenting the enormous genetic heterogeneity and diverse perturbations in human biology underlying NDDs. We propose 86 candidate disease-trait-associated genes for an NDD phenotype. Importantly, on the basis of objective and internally established variant prioritization criteria, we identified 51 families (51/176 = 28.9%) with multilocus pathogenic variation (MPV), mostly driven by runs of homozygosity (ROHs) - reflecting genomic segments/haplotypes that are identical-by-descent. Furthermore, with the use of additional bioinformatic tools and expansion of ES to additional family members, we established a molecular diagnosis in 5 out of 20 families (25%) who remained undiagnosed in our previously studied NDD cohort emanating from Turkey.

Genes that Affect Brain Structure and Function Identified by Rare Variant Analyses of Mendelian Neurologic Disease.

Development of the human nervous system involves complex interactions among fundamental cellular processes and requires a multitude of genes, many of which remain to be associated with human disease. We applied whole exome sequencing to 128 mostly consanguineous families with neurogenetic disorders that often included brain malformations. Rare variant analyses for both single nucleotide variant (SNV) and copy number variant (CNV) alleles allowed for identification of 45 novel variants in 43 known disease genes, 41 candidate genes, and CNVs in 10 families, with an overall potential molecular cause identified in >85% of families studied. Among the candidate genes identified, we found PRUNE, VARS, and DHX37 in multiple families and homozygous loss-of-function variants in AGBL2, SLC18A2, SMARCA1, UBQLN1, and CPLX1. Neuroimaging and in silico analysis of functional and expression proximity between candidate and known disease genes allowed for further understanding of genetic networks underlying specific types of brain malformations.

The relation of PON1-L55M gene polymorphism and clinical manifestation of Behcet's disease.

PURPOSE: Behçet's disease is a multisystem disease characterized by recurrent oral and genital ulcers, relapsing uveitis, mucocutaneous, articular, gastrointestinal, neurologic, and vascular manifestations. Paraoxonase is believed to play an important role in protection of LDL and HDL particles from oxidation, in antioxidant effect against lipid peroxidation on cellular membranes, and in anti-inflammatory process. Lipid peroxidation and free oxygen radicals have been thought to play a role in pathogenesis of BD. The association of paraoxonase gene polymorphisms with Behçet's Disease in a group of Turkish patients with clinical manifestations and healthy controls has been investigated. PATIENTS AND METHODS: Paraoxonase (PON-1-L55M) gene polymorphism was investigated in 50 Behcet patients and 50 healthy individuals with a PCR/RFLP method. RESULTS: There were significant differences between patients and the control group in allele frequencies of the PON1 L55M polymorphism (p=0.04). Also, when patients were compared with the control group according to clinical manifestations, this statistical significance was getting sharper. Compared with the PON55 L allele, the M allele was associated with greater than 3.5 fold (OR 3.5, 95% CI 1.3-8.9) increased risk of ocular (OR 2.4, 95% CI 1.1-5.3), 2.4 fold joint and 3.1 fold (OR 3.1, 95% CI 1.1-8.4) central nervous system manifestations of BD. CONCLUSION: The PON L55M gene polymorphism seemed to play a role in the pathogenesis of BD.

Interleukin 18 gene polymorphism is a risk factor for multiple sclerosis.

Proinflammatory cytokines with immunosuppressive properties play an important role in the pathogenesis of multiple sclerosis (MS). Interleukin 18 (IL-18) is one of the most important innate cytokines produced from macrophages in the early stages of the inflammatory immune response. The purpose of this study was to determine whether there was any relationship between IL18 gene polymorphisms and MS. IL18 genotyping were performed in 101 MS patients and 164 control subjects by using the PCR-restriction fragment length polymorphism (PCR-RFLP) method. The frequency of MS patients with the CC genotype of the IL18 gene at position -137 was significantly higher than with the GG genotype [p = 0.01, odds ratio (OR) 3.17]. In haplotype analysis of two SNPs in the IL18 gene, frequency of the CC haplotype was significantly higher in MS patients (p = 0.002, OR 3.0). However, the genotype distribution of the IL18 -607 C/A polymorphism in the MS patient group was not significantly different from that of the control group. These data suggest that IL18 gene polymorphisms at position -137 might be a genetic risk factor for MS in the Turkish population.