The last few weeks, we’ve been discussing some of the complicated history and science surrounding vaccination and immunity. The strategic and targeted defensive strategies employed by the immune system are by no means perfectly impregnable, but they represent several millennia of evolution under fire. Pathogens have always had a leg up on multicellular organisms—evolving more quickly and chaotically, unburdened by the constraints of form and function. They aren’t very sophisticated, but in terms of sheer brute force, there are already more viruses on earth than there are stars in the entire universe. We are besieged on all sides by these…
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So far, we’ve discussed the historical legacy of vaccines as man-made enhancements for our existing immune weaponry. And we’ve taken a look at some of the extensive defenses of the innate immune system that guard us day and night from the billions of natural viruses and bacteria roaming the earth. But like any fortress, there are vulnerabilities to be exploited. One way or another, pathogens can occasionally slip through and start using the body’s resources to replicate and cause major damage. In these cases, the immune system has to switch tactics from defensive to offensive. The first step is raising…
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For most of history and the long origin story of vaccines, we have known very little about the mechanics of how bodies defend against disease. The practice of variolation—purposefully exposing individuals to dried infected material to stimulate immunity—was borne out of the simple observation that people who survive sickness don’t tend to get sick again. The science of immunity didn’t really fall under much scientific scrutiny until the 19th century after Edward Jenner made his pivotal cowpox/smallpox vaccine discovery. Cowpox and smallpox were clearly different diseases with differences in severity, animal host, and mode of transmission. But, despite these differences,…
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In 2016, in a Mexican hospital, Dr. John Zhang and his team delivered a baby boy who had three genetic parents. The boy was conceived via in vitro fertilization (IVF) and a novel method called spindle nuclear transfer. Spindle nuclear transfer involves transferring the mixed DNA from the mother and father to a new donor egg from a third person. In this case, the boy’s mother had a rare neurological disorder called Leigh syndrome caused by a defect in her mitochondrial DNA (mtDNA). As I mentioned last week, mtDNA is passed directly from the mother through the mitochondria in her…
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These past few weeks, I have written about many different genetic disorders and risk factors that stem from inherited errors in the DNA or mistakes in the division of chromosomes. But this week, I want to pivot a bit to talk about disorders that originate in a special form of DNA called mitochondrial DNA (mtDNA). Most of the DNA in your cells is housed within the nucleus, a central organelle (literally “little organ”—organelles are the “organs” of your cell with their own specific function). The nucleus keeps the DNA separate from all of the enzymes and chemical reactions of the…
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Last week, I explained that most individuals have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes (for a total of 46 chromosomes all together). But a subset of people has chromosomal abnormalities in the form of an extra chromosome or a missing chromosome. Most chromosome abnormalities are fatal and result in early miscarriages, but some abnormalities are survivable. One of the most common survivable chromosome abnormalities is Down syndrome, in which there are three copies of chromosome 21 instead of two (known as a trisomy). The extra chromosome copy causes physical, mental, and developmental abnormalities. There are…
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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…
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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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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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