Can pills made from powdered scorpions and cockroaches REALLY stop you dying from a heart attack?

Genome: The Autobiography Of A Species In 23 Chapters

Harpercollins, 352 pages, $26.00, 1999 0060194979ISBN: 0-060-19497-9

Matt Ridley begins his book with a simple truth. "The human genome—the complete set of human genes—comes packaged in twenty-three separate pairs of chromosomes." We all know that. Nonetheless, Ridley has made the obvious seem novel by arranging his book around chromosomes. The idea came out of a conversation Ridley had with David Haig, an evolutionary biologist who said that chromosome 15 is his favorite because it has all sorts of "mischievous genes on it." That set the author thinking. "I had never thought of chromosomes as having personalities before…. But Haig's chance remark planted an idea in my head…."

Ridley decided to use each chromosome as the starting point for a story about particularly interesting genes and what we know (and don't know) about them. As a literary construct it works well. The book is, in its way, a selective text on human genetics that by and large avoids sounding like a classroom lecture. Genome is a treasure trove of fascinating bits of data, and it begins logically enough with history and moves along, chromosome by chromosome. Chromosome 4 is called Fate, because a certain gene that inevitably causes disease resides there. Chromosome 5, Environment, delves into the relationship between genes and things that turn them on or off. Chromosome 11 is home to genes that affect personality; chromosome 20 is the starting point for a discussion of prions, scrapie, mad-cow disease and the politics that go with them.

Early in the century, DNA had, as Ridley rightly says, "few fans," despite prescient speculation by a handful of scientists that genes are made of DNA. DNA was first isolated in 1869 from the pus-soaked bandages of wounded soldiers in Germany by a Swiss doctor named Friedrich Miescher. Several years later, Miescher guessed that DNA is the stuff of heredity, "just as the words and concepts of all languages can find expression in 24–30 letters of the alphabet." But the idea was not taken seriously until much later.

As Ridley takes up his story, chromosome by chromosome, his skill as a journalist–author is apparent. (Ridley was a science journalist at The Economist before he became a full-time book writer.) Take the case of chromosome 4, which is home to the gene for Wolf-Hirschhorn syndrome, a rare and deadly disease that leads to early death, and to the gene for Huntington disease, which causes slow but certain neurological devastation in patients in mid-life.

Using Wolf-Hirschhorn as his case study, Ridely tackles the concept that genes cause disease. "Wrong. We all have the Wolf-Hirschhorn gene," he writes. The disease develops in individuals who do not have it. "Their sickness is caused by the fact that the gene is missing altogether." The same gene, when mutated, causes Huntington chorea. It is only because we know what happens when the gene is missing or mutated that we think of it as a "disease gene." Some day, when through genomic science we learn what its normal function is, the gene may acquire a new identity altogether.

However, we do know a lot about how the mutated gene leads to Huntington disease, and it is a good way to examine the importance of genetic repeats and human polymorphisms. The gene contains but a single 'word'—CAG—which is repeated over and over again. If your gene says "CAG" no more than 10 or 15 times—that is, if you have 10–15 'repeats'—you have a healthy version. If it says "CAG" 39 times or more, "you will in mid-life slowly start to lose your balance, grow steadily more incapable of looking after yourself and die prematurely." The higher the number of CAG repeats, the earlier the onset of disease. The relationship between genetic language and health is pretty compelling, and Ridley does a superb job of making it vividly clear.

But when Ridley ventures into a discussion of the human genome project and ongoing efforts to sequence the human genome, his analysis is brief, very superficial, and misinformed. For example, he writes that the whole-genome 'shotgun' method for sequencing, "ignores the 97% of the text that is silent," concentrating on expressed genes alone. He confuses the whole-genome shotgun technique, which has been used successfully to completely and accurately decipher almost half of the genomes sequenced so far, with the Expressed Sequence Tag (EST) technique for gene discovery. Suffice it to say that Ridley's talent for writing genetic science is not matched by his writing about current genomic science. Fortunately his attempts are limited and only slightly distract from an otherwise good introduction to genetics.

Trisomy 21 Causes Down Syndrome

One could argue that the presence of extra copies of chromosome 21 in DS patients is only a correlation between an abnormality and the disease. However, scientists have developed trisomic mouse models that display symptoms of human DS, providing strong evidence that extra copies of chromosome 21 are, indeed, responsible for DS. It is possible to construct mouse models of DS because mouse chromosomes contain several regions that are syntenic with regions on human chromosome 21. (Syntenic regions are chromosomal regions in two different species that contain the same linear order of genes.) With mapping of the human and mouse genomes now complete, researchers can identify syntenic regions in mouse and human chromosomes with great precision.

As shown in Figure 4, regions on the arms of mouse chromosomes 10 (MMU10), 16 (MMU16), and 17 (MMU17) are syntenic with regions on the long q arm of human chromosome 21. Using some genetic tricks, scientists have induced translocations involving these mouse chromosomes, producing mice that are trisomic for regions suspected to play a role in DS. (Note that these are not perfect models, because the trisomic regions contain many mouse genes in addition to those that are syntenic to human chromosome 21 genes.) These experiments have shown that genes from MMU16 are probably most important in DS, because mice carrying translocations from MMU16 display symptoms more like human DS than mice carrying translocations of MMU10 or MMU17.

Additional experiments have tried to identify particularly important genes within this region by transferring smaller segments of the interval on MMU16. For example, the three mouse models depicted on the right in Figure 4 carry different portions of MMU16, and all display some symptoms of DS. Of the three, the most faithful model of DS is the Ts65Dn mouse, which carries 132 genes that are syntenic with human chromosome 21. This particular mouse demonstrates many of the symptoms of human DS, including altered facial characteristics, memory and learning problems, and age-related changes in the forebrain.

These results are both daunting and promising. On one hand, they suggest that there will be no magic bullet for treating DS, because large numbers of genes are most likely involved in the condition. On the other hand, the results suggest that mouse models will be useful in developing treatments for the many DS patients around the world.

Figure 4: Regions of synteny between human chromosome 21 (HSA21) and mouse chromosomes (MMUs) 16, 17, and 10.

There are three partial trisomy mouse models of human trisomy 21, all trisomic for a portion of MMU 16. The gene content of these partial trisomies is shown on the right.

Family Of Girl With Wolf-Hirschhorn Syndrome Aims To Raise Awareness Of Rare Disease

Family of girl with Wolf-Hirschhorn Syndrome aims to raise awareness of rare disease - CBS Chicago

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Raising a child with special needs can sometimes feel isolating, especially with a diagnosis of a rare disease that not many know about. The Hill family in Naperville knows that life after the birth of their twins. Their daughter Mary had stolen their hearts and given them a reason to reach out to use to raise awareness about her condition.

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