C282Y and H63D Polymorphisms in Hemochromatosis Gene and Risk of Parkinson's Disease: A Meta-Analysis

Common and rare variants in HFE are not associated with Parkinson's disease in Europeans

A recent study suggested that the p.H63D variant in HFE, a gene involved in iron homeostasis, may modify α-synuclein pathology, the pathological hallmark of Parkinson's disease (PD). If indeed this gene and specific variant are involved in PD, we expect to find differential distribution of HFE variants when comparing PD patients and controls. We analyzed genome-wide association study (GWAS) data from 14,671 PD patients and 17,667 controls and full sequencing data from additional 1647 PD patients and 1050 controls, using logistic regression models, and burden and Kernel tests. The HFE p.H63D variant was not associated with PD, nor did all the other common variants in the HFE locus. We did not find association of rare HFE variants with PD as well in all types of burden and Kernel tests. Our results do not support a role for HFE in PD risk.

The roles of iron and HFE genotype in neurological diseases

Iron accumulation is a recurring pathological phenomenon in many neurological diseases including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and others. Iron is essential for normal development and functions of the brain; however, excess redox-active iron can also lead to oxidative damage and cell death. Especially for terminally differentiated cells like neurons, regulation of reactive oxygen species is critical for cell viability. As a result, cellular iron level is tightly regulated. Although iron accumulation related to neurological diseases has been well documented, the pathoetiological contributions of the homeostatic iron regulator (HFE), which controls cellular iron uptake, is less understood. Furthermore, a common HFE variant, H63D HFE, has been identified as a modifier of multiple neurological diseases. This review will discuss the roles of iron and HFE in the brain as well as their impact on various disease processes.

MicroRNAs and Target Genes As Biomarkers for the Diagnosis of Early Onset of Parkinson Disease

Among the neurodegenerative disorders, Parkinson's disease (PD) ranks as the second most common disorder with a higher prevalence in individuals aged over 60 years old. Younger individuals may also be affected with PD which is known as early onset PD (EOPD). Despite similarities between the characteristics of EOPD and late onset PD (LODP), EOPD patients experience much longer disease manifestations and poorer quality of life. Although some individuals are more prone to have EOPD due to certain genetic alterations, the molecular mechanisms that differentiate between EOPD and LOPD remains unclear. Recent findings in PD patients revealed that there were differences in the genetic profiles of PD patients compared to healthy controls, as well as between EOPD and LOPD patients. There were variants identified that correlated with the decline of cognitive and motor symptoms as well as non-motor symptoms in PD. There were also specific microRNAs that correlated with PD progression, and since microRNAs have been shown to be involved in the maintenance of neuronal development, mitochondrial dysfunction and oxidative stress, there is a strong possibility that these microRNAs can be potentially used to differentiate between subsets of PD patients. PD is mainly diagnosed at the late stage, when almost majority of the dopaminergic neurons are lost. Therefore, identification of molecular biomarkers for early detection of PD is important. Given that miRNAs are crucial in controlling the gene expression, these regulatory microRNAs and their target genes could be used as biomarkers for early diagnosis of PD. In this article, we discussed the genes involved and their regulatory miRNAs, regarding their roles in PD progression, based on the findings of significantly altered microRNAs in EOPD studies. We also discussed the potential of these miRNAs as molecular biomarkers for early diagnosis.

Excessive early-life dietary exposure: a potential source of elevated brain iron and a risk factor for Parkinson's disease

Iron accumulates gradually in the ageing brain. In Parkinson's disease, iron deposition within the substantia nigra is further increased, contributing to a heightened pro-oxidant environment in dopaminergic neurons. We hypothesise that individuals in high-income countries, where cereals and infant formulae have historically been fortified with iron, experience increased early-life iron exposure that predisposes them to age-related iron accumulation in the brain. Combined with genetic factors that limit iron regulatory capacity and/or dopamine metabolism, this may increase the risk of Parkinson's diseases. We propose to (a) validate a retrospective biomarker of iron exposure in children; (b) translate this biomarker to adults; (c) integrate it with in vivo brain iron in Parkinson's disease; and (d) longitudinally examine the relationships between early-life iron exposure and metabolism, brain iron deposition and Parkinson's disease risk. This approach will provide empirical evidence to support therapeutically addressing brain iron deposition in Parkinson's diseases and produce a potential biomarker of Parkinson's disease risk in preclinical individuals.