Introduction
Genes perform more functions than just determining the color of the eyes or whether a person is tall or short. At the core of what defines a person as human lies their genes. Genes produce the proteins that run everything in the human body. Some proteins are visible, like the ones that compose hair and skin. Others work out of sight, coordinating the basic biological functions. Most of the time, every cell in the body contains exactly the same genes, but inside individual cells, some genes can be active while others are not. When genes are active, they can produce proteins, which is called gene expression. When genes are not active, they become dormant or unreachable for creating proteins.
Roughly one-third of the human genome, consisting of around 20,000 genes, is mainly active in the brain. The brain has the highest proportion of genes expressed in any part of the body, with at least a third of the approximately 20,000 genes in the human genome primarily expressed in it. These genes play a critical role in shaping the brain's development and function, and they ultimately regulate a person's movements, thoughts, emotions, and behaviors. Combined with the effects of the environment, changes in these genes can also determine whether a person is at risk for a particular disease and also the course it might follow.
What Role Do Genes Play in Memory Retention?
In a study data conducted, the researchers found that there are three types of repressive regulation going on with the genes. The first one was with the suppression of ribosomal protein-coding genes, the second one was in early translation repression of specific genes, and the third one was longer-term suppression that appeared later in a subgroup of genes by way of inhibition of estrogen receptor 1 signaling. The researchers also found that overexpressing the genes resulted in less memory retention as compared to forcing activation of estrogen receptor-1, which suggests that the receptor plays an important role in gene regulatory systems in the brain. These findings by the researchers suggest that one of the major functions of genes in memory retention is their suppression to prevent too much information from being stored, which further explains that genes in the hippocampus play an essential role in filtering out information that surrounds a learning event so that the brain will not be overfilled with unnecessary data.
Which Gene Is Responsible for Memory Decline?
Researchers have found genetic variants near the apolipoprotein E gene, which is known to harbor an increased risk of dementia, particularly Alzheimer's disease, was associated with poor memory performance, mostly in older people. Genetic variants associated with memory performance also predicted altered levels of expression of certain genes in the hippocampus, a key region of the brain for the consolidation of information. These were genes mainly involved in the metabolism of ubiquitin, which plays a crucial role in protein degradation. Human aging is characterized by increased interindividual differences in different areas of cognitive performance, like brain structure and brain function. There are multiple factors contributing to individual differences at neural and behavioral levels, which also include genetic predispositions and lifestyle factors. Recent evidence has shown that the effects of common genetic variations may increase in aging and contribute to inter-individual neural and cognitive differences, especially among older people.
What Is Apolipoprotein E (APOE)?
Apolipoprotein E is a lipoprotein that is involved in many steps of lipid homeostasis and injury repair in the brain. The e4 allele of apolipoprotein E is a strong risk factor for Alzheimer’s disease and is also associated with accelerated cognitive decline in normal aging. A meta-analysis revealed that e4 carriers have lower performance on several cognitive measures. Most importantly, apolipoprotein E-related effects were more pronounced in older individuals than younger ones with respect to global cognitive ability and episodic memory.
How Do Genes Contribute to Neurological Diseases?
The identification of the majority of single gene mutations that lead to rare neurological disorders such as Huntington's disease has been accomplished. In contrast, there is still so much to learn about the role of genetic variations in common neurological disorders and conditions, such as Alzheimer’s disease and stroke. It can be said that a few things are clear. The first thing is, for most people, a complex interplay between genes and the environment influences the risk of developing these diseases. Secondly, where specific genetic variations such as Single Nucleotide polymorphisms (SNPs) are known to affect disease risk, and the impact of any single variation is usually very small. To put it in simple words, most people affected by stroke or Alzheimer’s disease have experienced a combination of many ‘hits’ in the genome and in the environment.
What Are the Effects of APOE Gene on Cognitive Function and Dementia?
The effects of the APOE gene on cognition are explained below-
- APOE a4 Allele- Negative effects have been found with this gene on cognition with APOE e4 carriers. Compared to non-carriers, APOE e4 carriers exhibit worse cognitive performance and accelerated cognitive decline in healthy Alzheimer’s disease subjects.
- Promoter Polymorphisms of the APOE Gene- In addition to the risk for Alzheimer’s Disease, polymorphisms in the APOE gene promoter also affect cognition in older people.
- Genetic Association With the APOE Gene- Although the APOE gene explains some of the genetic risks associated with Alzheimer’s Disease, other genes may still modify the APOE e4 effect.
- Polygenic Risk Factors for Cognitive Decline- As cognition and Alzheimer’s Disease are highly heritable polygenic traits in humans, investigating polygenic effects on the phenotypes is also very important. Hence, researchers tend to integrate different genetic loci to construct polygenic risk scores (PGS), and the studies conducted confirmed that the polygenic genetic risk increases the incidence of Alzheimer’s Disease, the conversion rate of mild cognitive impairment to Alzheimer’s disease, and the risk of cognitive decline.
Conclusion
It can be concluded that genes do play a role in memory decline as well as memory retention. The APOE gene is a major factor for the same. But apart from this gene, there are many genes that affect cognitive function and also play a role in neurological diseases.
