Introduction
Gene defects have an essential part in the etiology of neurodegenerative diseases. Furthermore, the molecular pathways underlying the etiology and pathogenesis of many neurodegenerative conditions have been clarified due to the information acquired from genetic studies. With a focus on the similarities and differences between these syndromes, researchers investigate the current status of the genetic epidemiology of the most prevalent neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Lewy body dementia, frontotemporal dementia, amyotrophic lateral sclerosis, Huntington's disease, In this article, we will discuss the neurodegenerative disorders and associated genetics.
What Are Neurodegenerative Disorders?
Neurodegenerative disorders (NDD) are diverse conditions characterized by selective dysfunction and loss of neurons, glial cells, and the neural networks in the brain and spinal cord. It can affect many body activities, such as balance, movement, talking, breathing, mental functioning, and heart function. Many of these disorders are genetic. However, medical conditions, including alcoholism, tumors, or strokes, might be the root cause of the condition. Toxins, chemicals, and viruses are some other potential causes. Sometimes there is no known cause. NDDs are incurable and debilitating diseases that are becoming more common as the world's population ages.
What Are the Risk Factors for Developing Neurodegenerative Disorders?
Neurodegenerative disorders result from a mix of factors:
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Age: They become more likely as you age.
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Genetics: Family history can increase risk.
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Environment: Toxins, head injuries, and inflammation matter.
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Lifestyle: Unhealthy habits like smoking and poor diet can contribute.
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Vascular Health: Cardiovascular issues can play a role.
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Hormonal Changes: Shifts in hormones may matter.
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Mental Stimulation: Staying mentally active can help reduce risk.
What Is an Example of a Neurodegenerative Disorder?
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Alzheimer's disease.
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Parkinson's disease.
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Lewy body dementia.
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Amyotrophic lateral sclerosis.
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Huntington's disease.
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Spinal muscular atrophy.
What Are Alzheimer’s Disease and Its Associated Genetics?
Alzheimer's disease is the most prevalent progressive, irreversible cause of dementia. It is characterized by gradual memory and cognitive loss and the accumulation of Aβ deposits and neurofibrillary tangles in the brain. Family history is the most crucial risk factor for the disease. Alzheimer's disease is classified into two types, which include-
Late-Onset Alzheimer's Disease - LOAD is an Alzheimer's disease that manifests at age 65 or older and accounts for most AD patients. No specific gene has been identified as the direct cause of late-onset Alzheimer's disease. However, a person's risk is raised if they have a genetic variation of the apolipoprotein E (APOE) gene on chromosome 19. There are various alleles or variants of APOE.
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APOE ε2 is a rare gene that may offer some protection against the disease. This allele generally causes Alzheimer's disease to appear later in life than it would in someone with the APOE ε4 gene.
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APOE ε3 is the most common allele and neutralizes the condition, neither decreasing nor raising the risk.
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APOE ε4 is linked to an increased risk of Alzheimer's disease and an earlier age at which the disease manifests. The disease risk is increased by having one or two APOE ε4 alleles.
Early-Onset of Alzheimer's Disease - EOFAD accounts for a small proportion of all AD cases and mainly manifests in people under age 65, with autosomal dominant transmission within affected families. The following three single-gene changes are linked to the development of early-onset Alzheimer's disease-
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Amyloid precursor protein (APP) on chromosome 21.
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Presenilin 1 (PSEN1) on chromosome 14.
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Presenilin 2 (PSEN2) on chromosome 1.
Mutations in these genes cause the generation of abnormal proteins linked to the disease.
What Are Parkinson’s Disease and Its Associated Genetics?
The second most prevalent adult-onset neurodegenerative condition is Parkinson's disease. Numerous genes have been linked to Parkinson's disease, and some of the vital genes are listed below-
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SNCA- SNCA is responsible for the production of the protein alpha-synuclein. This protein forms Lewy bodies in the brain tissue of people with Parkinson's disease. Early-onset Parkinson's disease is associated with mutations in the SNCA gene.
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PARK2- The PARK2 gene produces the protein parkin, which usually aids cells in protein breakdown and recycling.
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PARK7- Mutations in this gene produce a rare type of Parkinson's disease with early onset. The PARK7 gene has the antioxidant DJ-1 protein, which protects against mitochondrial stress.
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PINK1- PINK1 produces a protein kinase that protects mitochondria (structures within cells) against stress. Early-onset Parkinson's disease is associated with PINK1 mutations.
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LRRK2- LRRK2 produces a protein kinase. Parkinson's disease with a late onset has been associated with mutations in the LRRK2 gene.
Depending on the genes involved, different inheritance patterns exist among inherited cases of Parkinson's. It is inherited from only one parent if the LRRK2 or SNCA genes are involved. A disease can occur when just one copy of a gene is mutated, known as an autosomal dominant pattern.
What Are Lewy Body Dementia and Its Associated Genetics?
Lewy body dementia (LBD) is the most prevalent form of degenerative dementia in older adults and a complex brain disorder. It is characterized by parkinsonism, recurring visual hallucinations, and increasing cognitive impairment. It has genetic variations in genes involved in pathogenic pathways leading to similar neurodegenerative diseases. It includes the amyloid precursor protein gene (APP), PD α-synuclein gene (SNCA ), presenilin one gene (PSEN1), and presenilin two genes (PSEN2 ).
What Is Huntington’s Disease and Its Association in Genetics?
Huntington's disease is a degenerative brain condition caused by a single faulty gene on chromosome 4. It is a "dominant" condition, which means that anyone who gets it from a parent will eventually have the disease. It is characterized by neuronal degeneration in the basal ganglia and cortex, which clinically results in chorea, psychiatric symptoms, and dementia.
What Are Prion Disorders?
Prion disorders contain a rare and heterogeneous spectrum of clinical and histological characteristics that are unique in the group of neurodegenerative diseases in that they can be familial. For example., Creutzfeldt-Jakob disease (CJD). , fatal familial insomnia (FFI), Gerstmann-Sträussler-Scheinker syndrome (GSS). Most variants are identified by fast-developing neurodegeneration and amyloid plaques composed of prion protein aggregates, most likely caused by self-propagation of abnormal or misfolded PrP.
Conclusion
Genetics is essential for understanding neurodegenerative disorders such as Lewy body dementia, Alzheimer's, Parkinson's, and Huntington's disease. Among all these, specific genes are critical for forming these disorders. Therefore, a thorough understanding of the genetic basis of neurodegeneration will be required to design and develop effective early prediction and preventive or treatment measures, to significantly lower the incidence of these devastating conditions.
