Over the past year, the SciWhys column has explored a number of different topics, from our immune system to plants, from viruses to DNA. But why is an understanding of topics such as these so important? In short, using science to understand our world can help to improve our lives. In this post and the next, I want to illustrate this point with an example of how progress in science is providing hope for the future for one family, and many others like them.
By Jonathan Crowe
Carys is an angelic-looking two-year old, with a truly winning smile. At first sight, then, she seems no different from any other child her age. Yet Carys’ smile belies a heart-rending reality: Carys has Rett syndrome, a disorder of the nervous system that is as widespread in the population as cystic fibrosis, yet is recognised to only a fraction of the same extent. (I, for one, had never heard of it until just a few months ago.)
Rett syndrome is a delayed onset disorder — something whose effects only become apparent with time. When Carys was born, she appeared perfectly healthy, and developed in much the same way as any other healthy infant. Just as she began to master her first few words, however, she lost the power of speech, and soon lost the use of her hands too. The effects of Rett syndrome were beginning to be felt.
Over time, Rett syndrome robs young girls of their motor control: they lose the ability to walk, to hold or carry objects, and to speak. But there be other complications too: there may be digestive problems; difficulties eating, chewing, and swallowing; and seizures and tremors. It is a truly debilitating disorder.
So what causes Rett syndrome? What’s happened inside the body of young girls like Carys? We know that the syndrome is caused by as little as a single error (a mutation) in a single gene. (As I mention in a previous post, it’s quite unsettling to realise that just one error in the tens of millions of letters that spell out the sequence of our genomes is sufficient to cause certain diseases. Sometimes there’s very little room for error.) The normal, healthy gene (called MECP2) contains the instructions for the cell to manufacture a particular protein; the mutated gene produces a broken form of this protein, which no longer functions as it should.
But how can a single protein affect so many processes – from speech to the movement of limbs? The answer lies in the way the protein interacts with other genes, particularly in brain cells. Essentially, the protein acts like a cellular librarian by helping the cells in the brain to make use of the information stored in their genomes (their libraries of genes). If the protein is broken, the cells can no longer make use of all of the genetic information needed for them to work properly (a bit like trying to use an instruction manual with some of the pages blacked out), so normal processes begin to break down. The broken protein doesn’t just affect the ability of the brain cells to use one or two other genes, but a whole range of them – and that’s why the effects of Rett syndrome are so wide-ranging.
But the story of Rett syndrome runs deeper than this. The mutation that causes Rett syndrome occurs in sperm; it happens after the sp
By: Lauren,
on 5/31/2011
Blog: OUPblog (Login to Add to MyJacketFlap)
JacketFlap tags: *Featured, allen wilcox, fertility and pregnancy, how to get pregnant, ovulation, wilcox, chromosome, menstrual cycle, how to have a boy, pregnancy myths, sex positions, menstrual, Health, myths, baby, sex, pregnancy, sperm, barbara kingsolver, nih, fertility, cycles, epidemiology, due date, Add a tag
By Allen J. Wilcox
On making boy babies, and other pregnancy myths
In her novel, Prodigal Summer, Barbara Kingsolver celebrates the lush fecundity of nature. The main character marvels at the way her ovulation dependably comes with the full moon.
It’s a poetic image – but is there any evidence for it?
Actually, no. It’s true that the length of the average menstrual cycle is close to the length of the lunar cycle. But like so many notions about fertility, an effect of the moon on ovulation is just a nice story. The menstrual cycle is remarkably variable, even among women who say their cycles are “regular.” This is not surprising – unlike the movement of stars and planets, biology is full of variation. The day of ovulation is unpredictable, and there is no evidence (even in remote tribal cultures) that ovulation is related to phases of the moon or other outside events.
We humans are susceptible to myths about our fertility and pregnancy. These myths also invade science. One scientific “fact” you may have heard is that women who live in close quarters synchronize their menstrual cycles. The paper that launched this idea was published forty years ago in the prestigious journal Nature1. Efforts to replicate those findings have been wobbly at best – but the idea still persists.
Another scientific myth is the notion that sperm carrying the Y male chromosome swim faster than sperm carrying the X female chromosome. It’s true that the Y chromosome is smaller than the X. But there is no evidence that this very small addition of genetic cargo slows down the X-carrying sperm. As often as this idea is debunked, it continues to appear in scientific literature – and especially the literature suggesting that couples can tilt the odds towards having a baby of a particular sex.
Choosing your baby’s sex
Many couples have a definite preference for the sex of their baby. The baby’s sex is established at conception, which has led to a lot of advice on things to do around the time of conception to favor one sex or the other. Recommendations include advice on timing of sex in relation to ovulation, position during sex, frequency of sex, foods to eat or avoid, etc. The good thing about every one of these techniques is that they work 50% of the time. (This is good enough to produce many sincere on-line testimonials.) Despite what you may read, there is no scientific evidence that any of these methods improves your chances for one sex or the other, even slightly. The solution? Relax and enjoy what you get.
When will the baby arrive?
Everyone knows that pregnancies last nine months – but do they? Doctors routinely assign pregnant women a “due-date,” estimated from the day of her last menstrual period before getting pregnant. The due-date is set at 40 weeks after the last menstrual period. You might think the due-date is based on scientific evidence, but in fact, 40 weeks was proposed in 1709 for a rather flaky reason: since the average menstrual period is four weeks, it seemed “harmonious” for pregnancy to last the equivalent of ten menstrual cycles.
So what are a woman’s chances of actually delivering on her due date? Fifty percent? Twenty percent?
Try four percent. Just like the length of menstrual cycles (and every other aspect of human biology), there is lots of variation in the natural length of pregnancy. If the due-date is useful at all, it is as the median length of pregnancy – in other words, about half of women will deliver before their due-date, and about half after. So don’t cancel your appointments on the due-date just because you think it’s The Day – there’s a 96% chance the baby will arrive some other time.
1. McClintock MK. Menstrual synchorony and suppression.
By: Lauren,
on 5/11/2011
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JacketFlap tags: Health, birth, pregnancy, sperm, cleavage, Thought Leaders, kamal, embryo, *Featured, how to get pregnant, birth rate, oxford journals, human reproduction, in vitro, in vitro fertilization, ivf, louise brown, menstrual cycle, ohss, ovarian, fertilization, vitro, regimens, sunkara, sesh, Add a tag
By Dr Sesh Kamal Sunkara
In vitro fertilization (IVF) involves the retrieval of an egg and fertilization with sperm in the laboratory (in vitro) as opposed to the process happening within the human body (in vivo), with a natural conception. IVF was first introduced to overcome tubal factor infertility but has since been used to alleviate all types of infertility and nearly four million babies have been born worldwide as a result of assisted reproductive technology.
The birth of Louise Brown in 1978, the world’s first IVF baby was from a natural menstrual cycle without the use of any stimulation drugs. As success rates were low with natural cycles in the early days of IVF, ovarian stimulation regimens were introduced into IVF to maximize success rates. The aim was to retrieve more eggs to overcome the attrition in numbers at fertilization, cleavage, and implantation. However, with the introduction of ovarian stimulation regimens the complication of ovarian hyperstimulation syndrome (OHSS) arose.
There have been several discussions among IVF clinicians on what the ideal number of eggs should be to optimize IVF outcome and minimize risk of OHSS. We analysed a large database of over 400, 000 cycles provided by the Human Fertilisation and Embryology Authority (HFEA) in order to establish the association between egg number and live birth rate in IVF.
We found that live birth rate increased with increasing number of eggs retrieved up to 15 eggs and plateaued from 15 to 20 eggs with a decline in live birth rate beyond 20. The analysis of the data suggested that around 15 eggs may be the optimal number to aim for in a fresh IVF cycle in order to maximize treatment success whilst minimizing the risk of OHSS. We also established a nomogram which is the first of its kind that allows prediction of live birth for a given egg number and female age group. This is potentially valuable for patients and clinicians in planning IVF treatment protocols and counselling regarding the prognosis for a live birth occurrence, especially in women with either predicted or a previous poor ovarian response.
The full paper and supplementary data has been made publicly available here, as published in Human Reproduction by Sesh Kamal Sunkara, Vivian Rittenberg, Nick Raine-Fenning, Siladitya Bhattacharya, Javier Zamora and Arri Coomarasamy. Above table appears with full permission from Human Reproduction and Oxford Journals.