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.

Background We aimed to identify the disease-causing mutations in a consanguineous family featuring intellectual disability and parkinsonism. Methods Full phenotypic characterization, followed by genome-wide SNP genotyping and whole genome sequencing, was carried out in all available family members. Results The chromosome 2p23.3 was identified as the disease-associated locus, and a homozygous PTRHD1 mutation (c.157C>T) was then established as the disease-causing mutation. The pathogenicity of this PTRHD1 mutation was supported by its segregation with the disease status, its location in a functional domain of the encoding protein, as well as its absence in public databases and ethnicity-matched control chromosomes. Conclusions Given the role of 2p23 locus in patients with intellectual disability and the previously reported PTRHD1 mutation (c.155G>A) in patients with parkinsonism and cognitive dysfunction, we concluded that the PTRHD1 mutation identified in this study is likely to be responsible for the phenotypic features of the family under consideration.

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.

The association of rs11240569 polymorphism in SLC41A1 gene with reduced risk of PD was replicated in our population.

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.