Last week we saw how the complex interplay of genetics and environment has impacted the inheritance of sickle-cell anemia. This week, I want to talk about a special subset of inherited diseases called sex-linked disorders. One of the most common sex-linked disorders is Duchenne muscular dystrophy (DMD), a debilitating muscular disorder linked to the X-chromosome. Sex-linked disorders, like DMD, come from genes in the sex chromosomes (X and Y in humans). Sex chromosomes are responsible for determining an individual’s biological sex, XX for female, XY for male (although there are other less common combinations that come from chromosomal aberrations—we’ll talk…
Comments closedCategory: Biochemistry
Last week, I discussed the genetic basis of cancer risk, specifically breast cancer. This week I want to start talking about direct genetic diseases, starting with a disease that has an interesting connection with malaria: sickle-cell anemia. Sickle-cell anemia affects millions of people worldwide, and it is particularly common in people with African or Mediterranean ancestry. Individuals with two sickle-cell disease (SCD) genes (one from their mother and one from their father) develop sickle-cell anemia, which causes their red blood cells to become warped and “sickle” shaped. These sickle cells are stiff and they tend to build up in the…
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The last few weeks, I’ve discussed how the efforts of the human genome project and next-generation sequencing have contributed to significant progress in the field of personalized medicine. Identifying the precise genetic basis of a disease can help scientists understand how the disease manifests, can help doctors diagnose and treat patients earlier, and could potentially unlock the ability to remove the disease through genetic editing. Many diseases have a genetic basis and not all of them are fully understood. Within this series, I will endeavor to uncover some of what scientists have learned about genetic diseases, disorders, and risk factors.…
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After the Human Genome Project was completed in 2003, scientists were looking for faster, cheaper, and more efficient sequencing methods than the Sanger Sequencing utilized in the 13-year project. In 2005, researchers at 454 Life Sciences (later acquired by Roche) developed the first Next-Generation Sequencing method called pyrosequencing. Since then, many other companies have developed their own Next-Generation Sequencing methods. The main Next-Generation Sequencing methods developed in the last two decades include a newer, improved pyrosequencing called Roche 454, Illumina’s Solexa Genome Analyzer series, and Ion Torrent sequencing. As scientists continue to develop newer and more efficient sequencing methods, it…
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Last week, I wrote about the potential of personalized medicine, and I briefly mentioned the role of genetic sequencing and the Human Genome Project (HGP) in making personalized medicine possible. This week, I want to delve a little deeper into what exactly goes into sequencing a genome. The HGP, which took 13 years to complete, was performed using a process known as Sanger sequencing. Sanger sequencing, invented in 1977 by Fred Sanger, is a laborious and costly process of sequencing. In the HGP, relatively tiny fragments of the human genome were sequenced multiple times and aligned together, piece by piece,…
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The last few weeks, I have written about the complex molecular immunity mechanism of CRISPR and how we can harness it to precisely edit genes in a gamut of cells. But the ability of CRISPR to treat genetic disorders, predispositions, and susceptibilities relies on our understanding of the genetic basis of disease. Since the completion of the Human Genome Project (HGP) in 2003, which sought to sequence the entire human genome, scientists have made great strides in connecting diseases and disorders with their genetic backgrounds. In the meantime, the invention of Next Generation Sequencing (NGS) in 2006 has drastically reduced…
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In November of 2018, Jiankui He, a Chinese biophysicist, announced to the world that he had created the first ever CRISPR-edited human babies. The experiment resulted in twin girls, Lulu and Nana, who developed from embryos with a modified version of the CCR5 gene meant to increase resistance to HIV. The experiment was riddled with breaches and blunders, and it quickly became an international scandal. At the end of 2019, He was sentenced to three years in prison for “illegal medical practices.” All of the flaws in He’s experiment highlight just how far we still have to go before embryonic…
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CRISPR-Cas9 has made genetic engineering easier, faster, and cheaper than ever before. A scientist interested in manipulating a particular gene only needs to search the gene’s sequence for a suitable PAM. Once a PAM is found, the corresponding Cas9 can be ordered or harvested from its bacterial strain (and as I mentioned last week, even if a PAM isn’t found, it is possible to engineer a Cas9 to recognize a new PAM sequence). An appropriate sgRNA (the crRNA:tracrRNA fusion molecule) can be designed by identifying the target sequence 20 nucleotides upstream of the chosen PAM. These sgRNA’s can be engineered…
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If you’ve ever seen the movie Gattaca, then you probably know something about the concept of genetic engineering. However fictionalized that movie may have seemed (my favorite part was a full genome sequence printed on one small tube of rolled up paper), it did bring up a lot of interesting ethical questions that are suddenly becoming more and more relevant. Widespread genetic engineering isn’t yet a reality, but it certainly could be within our lifetime. In the last decade, scientists have discovered a way to hijack the CRISPR-Cas9 system in bacteria to make efficient and targeted genetic editing possible. However, as we…
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The last few weeks, we’ve talked a lot about the immune system and how it builds and maintains immunity to viral pathogens, like Covid-19. This week, I’d like to shift a bit to a different form of immunity that doesn’t have anything to do with the coronavirus (I know, a blog post that’s not about Covid-19—shocking) but one that has had major implications in the field of genetic engineering: bacterial immunity to viral infection. I mentioned briefly in my post about viruses that a large subset of viruses infect bacteria, called bacteriophages. Although bacteria are far less complex than humans are, they…
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