Novel Genes

Some genetic brain disorders are due to random gene mutations or mutations caused by environmental exposure, such as cigarette smoke. Other disorders are inherited, which means that a mutated gene or group of genes is passed down through a family. They can also be due to a combination of both genetic changes and other outside factors.

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Some examples of genetic brain disorders include

Leukodystrophies
Phenylketonuria
Tay-Sachs disease
Wilson disease
Many people with genetic brain disorders fail to produce enough of certain proteins that influence brain development and function. These brain disorders can cause serious problems that affect the nervous system. Some have treatments to control symptoms. Some are life-threatening.Novel Genes And Brain Disorders Development Essay

When most people consider the genetic basis of disease, they might think about the rare, single gene disorders, such as cystic fibrosis (CF), phenylketonuria or haemophilia, or perhaps even cancers with a clear heritable component (for example, inherited predisposition to breast cancer). However, although genetic disorders are individually rare, they account for approximately 80% of rare disorders, of which there are several thousand. The sheer number of rare disorders means that, collectively, approximately 1 in 17 individuals are affected by them. Moreover, our genetic constitution plays a role, to a greater or lesser extent, in all disease processes, including common disorders, as a consequence of the multitude of differences in our DNA. Some of these differences, alone or in combinations, might render an individual more susceptible to one disorder (for example, a type of cancer), but could render the same individual less susceptible to develop an unrelated disorder (for example, diabetes). The environment (including lifestyle) plays a significant role in many conditions (for example, diet and exercise in relation to diabetes), but our cellular and bodily responses to the environment may differ according to our DNA. The genetics of the immune system, with enormous variation across the population, determines our response to infection by pathogens. Furthermore, most cancers result from an accumulation of genetic changes that occur through the lifetime of an individual, which may be influenced by environmental factors. Clearly, understanding genetics and the genome as a whole and its variation in the human population, are integral to understanding disease processes and this understanding provides the foundation for curative therapies, beneficial treatments and preventative measures.Novel Genes And Brain Disorders Development Essay

With so many genetic disorders, it is impossible to include more than a few examples within this review, to illustrate the principles. For further information on specific conditions, there are a number of searchable internet resources that provide a wealth of reliable detail. These include Genetics Home Reference (https://ghr.nlm.nih.gov/), Gene Reviews (https://www.ncbi.nlm.nih.gov/books/NBK1116/), the ‘Education’ section from the National Human Genome Research Institute (https://www.genome.gov/education/) and Online Mendelian Inheritance in Man (https://www.omim.org/). In this review, an understanding and knowledge of basic principles and techniques in molecular biology, such as the structure of DNA and the PCR will be assumed, but explanations and animations of PCR (and some other processes) are available from the DNA Learning Center (https://www.dnalc.org/resources/). The focus here will be on human disease, although much of the research that defines our understanding comes from the study of animal models that share similar or related genes.

The human genome and variation
The human genome and the human genome reference sequence
The complete instructions for generating a human are encoded in the DNA present in our cells: the human genome, comprising roughly 3 billion bp of DNA. Scientists from across the world collaborated in the ‘Human Genome Project’ to generate the first DNA sequence of the entire human genome (published in 2001), with many additions and corrections made in the following years. Genome sequence information for humans and many other species is freely accessible through a number of portals, including the National Center for Biotechnology Information (NCBI; https://www.ncbi.nlm.nih.gov/) and Ensembl (http://www.ensembl.org/), which also provide a wealth of related information.Novel Genes And Brain Disorders Development Essay

The majority of our DNA is present within the nucleus as chromosomes (the nuclear DNA or nuclear genome), but there is also a small amount of DNA in the mitochondria (the mtDNA or mitochondrial genome). Most individuals possess 23 pairs of chromosomes (Figure 2), therefore much of the DNA content is present in two copies, one from our mother and one from our father.

The human nuclear genome encodes roughly 20000 protein-coding genes, which typically consists of both protein-coding (exon) and non-coding (intron) sequences. Our genome also contains roughly 22000 genes that encode RNA molecules only; some of these RNAs form components of the translation machinery (rRNA, tRNA) but there are many more that perform various roles within the cell, including regulation of expression of other genes. In fact it is now believed that as much as 80% of our genome has biological activity that may influence structure and function. The human genome also contains over 14000 ‘pseudogenes’; these are imperfect copies of protein-coding genes that have lost the ability to code for protein. Although originally considered as evolutionary relics, there is now evidence that some may be involved in regulating their protein-coding relatives, and in fact dysregulation of pseudogene-encoded transcripts has been reported in cancer. Additionally, sequence similarity between a pseudogene and its normal counterpart may promote recombination events which inactivate the normal copy, as seen in some cases of perinatal lethal Gaucher disease. Furthermore, some pseudogenes have the potential to be harnessed in gene therapy to generate functional genes by gene editing approaches. The distribution of genes between chromosomes is not equal: chromosome 19 is particularly gene-dense, while the autosomes for which trisomy is viable (13, 18, 21) are relatively gene-poor  Novel Genes And Brain Disorders Development Essay

The researchers found that this gene, C11orf46, is an important regulator during brain development. Specifically, it turns on and off the direction-sensing proteins that help guide the long fibers growing out of newly formed neurons responsible for sending electrical messages, helping them form into a bundle, which connects the two hemispheres of the brain. Failure to properly form this bundled structure, known as the corpus callosum, can lead to conditions such as intellectual disability, autism or other brain developmental disorders.Novel Genes And Brain Disorders Development Essay

“Although this work is early, these findings suggest that we may be able to develop future epigenome editing therapies that could help reshape the neural connections in the brain, and perhaps prevent developmental disorders of the brain from occurring,” says Atsushi Kamiya, M.D., Ph.D., associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine.

The study was published online in the September 11 issue of Nature Communications.

WAGR syndrome is also known as chromosome 11p13 deletion syndrome, which can result when some or all of the gene located in the region of chromosome 11p13 that includes C11orf46 is deleted by chance. The researchers used a genetic tool, short hairpin RNA, to cause less of the C11orf46 protein to be made in the brains of mice. The fibers of the neurons in the mouse brains with less of the C11orf46 protein failed to form the neuron bundled corpus callosum, as is found in WAGR syndrome.Novel Genes And Brain Disorders Development Essay

The gene that makes Semaphorin 6a, a direction-sensing protein, was turned on higher in mice with lower C11orf46. By using a modified CRISPR genome editing system, the researchers were able to edit a portion of the regulatory region of the gene for Semaphorin. This editing of the epigenome allowed C11orf46 to bind and turn down the gene in the brains of these mice, which then restored the neuron fiber bundling to that found in normal brains.

Other authors on the study include Atsushi Saito, Yuto Hasegawa, Yuya Tanaka, Mohika Nagpal, Gabriel Perez and Emily Alway of Johns Hopkins; Cyril Peter, Sergio Espeso-Gil, Tariq Fayyad, Chana Ratner, Aslihan Dincer, Achla Gupta, Lakshmi Devi and Schahram Akbarian of Mount Sinai; John Pappas of New York University; François Lalonde of the National Institute of Mental Health (NIMH), John Butman of the National Institutes of Health (NIH) Clinical Center; and Joan Han of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).Novel Genes And Brain Disorders Development Essay

This work was supported by grants from the National Institute on Drug Abuse (DA041208), NIMH (MH091230, MH094268, MH104341, MH117790), the National Center for Complementary and Integrative Health (AT008547), a Johns Hopkins Catalyst Award, the Brain & Behavior Research Foundation, NICHD (ZIAHD008898), an NIH Bench-to-Bedside Award and Office of the Director at NIH (S10OD016374). Novel Genes And Brain Disorders Development Essay

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