Closer Kinship Linked With Reproductive Success

In a paper published 7 Feb 2008 deCODE scientists establish a substantial and consistent positive correlation between the kinship of couples and the number of children and grandchildren they have. The study, which analyzes more than 200 years of deCODE's comprehensive genalogical data on the population of Iceland, shows that couples related at the level of third cousins have the greatest number of offspring. For example, for women born between 1800 and 1824, those with a mate related at the level of a third cousin had an average of 4.04 children and 9.17 grandchildren, while those related to their mates as eighth cousins or more distantly had 3.34 children and 7.31 grandchildren. For women born in the period 1925-1949 with mates related at the degree of third cousins, the average number of children and grandchildren were 3.27 and 6.64, compared to 2.45 and 4.86 for those with mates who were eighth cousins or more distantly related.

The findings hold for every 25-year interval studied, beginning with those born in the year 1800 up to the present day. Because of the strength and consistency of the association, even between couples with very subtle differences in kinship, the authors conclude that the effect very likely has a biological basis, one which has yet to be elucidated. The paper, 'An association between the kinship and fertility of human couples,' is published online in Science magazine at www.sciencemag.org.

This study provides the most comprehensive answer yet to the longstanding question of how kinship affects fertility in humans. Previous studies in other parts of the world have suggested that the two phenomena are positively correlated, though confounding variables, such as the impact of socioeconomic status on the size of families or age at marriage, have made the results difficult to interpret. The analysis of such a long-term series of data from Iceland effectively eliminates these variables by encompassing an entire population which has historically been highly homogeneous both culturally and economically. Moreover, the results are strikingly consistent from eras in which Iceland was a predominantly poor and rural country, to the present-day era of a highly urbanized society with one of the highest standards of living in the world.

The authors note that the findings are somewhat counterintuitive from an evolutionary perspective because closely-related parents have a higher probability of having offspring homozygous for deleterious recessive mutations, although closer parental kinship can also decrease the likelihood of immunological incompatibility between mother and offspring, for example in rhesus factor blood type. Perhaps most importantly, today's findings also suggest that the recent and dramatic demographic shift experienced in Iceland - from a rural society to a highly urbanized one - may serve to slow population growth, as individuals are exposed to a much broader range of distantly related potential mates. If so, this could be of relevance to slowing population growth in the many other - and much more populous - societies around the world undergoing transition from closely-knit rural societies to more urbanized ones. Indeed, the UN estimates that in the 2007-2008 period the majority of the world's population will, for the first time in human history, live in town and cities.

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'Miracle baby' conceived from 22-year-old sperm

A Canadian couple successfully conceived a baby boy after using sperm that had been stored 22 years, two months and two weeks - a likely record for Canadian fertility treatment. The longest-known storage period for sperm resulting in a live birth is 28 years, according to a 2005 data report in the American journal Fertility and Sterility. Jacek was born in Langley, Canada on 1 November 2007 thanks to Mike Kuzminski's discovery that a Calgary clinic, where he had stored sperm years ago prior to cancer treatment which rendered him infertile, had continued to store his sperm despite no contact or payment from Kuzminski in 22 years.Kuzminski, now a 43-year-old, was diagnosed with Hodgkin's lymphoma at 18. Because chemo and radiotherapy treatment caused 20 per cent of patients to become infertile in the 1980's - a risk that is significantly lower today - his doctor recommended that Kuzminski freeze his sperm. He did and then underwent three years of on-and-off treatment that led to his later-confirmed infertility. When he and his wife Kristin married in 2003, they had accepted that they would not be able to have children. Kuzminski had since forgotten he had frozen sperm before his treatment years ago until his sister reminded him. 'I had assumed that after 15 or 20 years the hospital had gotten rid of my sperm', he said but instead surprisingly found that the clinic had kept it and he owed Rs. 90,000 in storage fees.
Kuzminski seems to have benefited from Canada's current policy indecision regarding gamete storage time-limit guidelines for abandoned frozen sperm. He would not have been so lucky in the UK, where gametes are stored for a maximum of ten years, now with the option to request a five year extension.
Despite great anxiety regarding use of a limited supply of sperm and low success rates of fertility treatments, Jacek was born after undergoing only two intra-uterine insemination (IUI) procedures. They have enough sperm remaining for 19 more attempts but are focusing on their new parenthood and postponing consideration of whether they will try to have another child.

Insulin-secreting cells produced by stem cells

Scientists in the US have derived insulin-producing cells from human embryonic stem cells (hESCs), and have successfully implanted them into mice. The achievement, reported last week in the journal Nature Biotechnology, could help push forward research into therapies for diabetes. Type 1 diabetes, and some forms of type 2 diabetes, are caused by a deficiency of pancreatic beta cells. These are cells that produce insulin, the hormone that helps control blood glucose levels, and are part of clusters of hormone-producing cells in the pancreas called the islets of Langerhans. The disease is characterised by a lack of insulin and subsequent misregulation of blood glucose, a condition that can be fatal. Diabetes is currently the seventh leading cause of death in the US, with 200,000 deaths reported per year.
The scientists at Novocell Inc. in San Diego, led by Dr Emmanuel E. Baetge, the chief scientific officer, derived immature precursor pancreatic beta cells from hESCs. They then implanted them into mice whose own beta cells had been destroyed by chemical treatment. After 90 days, the mice had switched the precursor cells into mature beta cells that produced insulin again, which helped control blood glucose. The implanted cells were said to be 'functionally and morphologically similar' to normal beta cells.Transplanting human islet cells into diabetic patients from donated pancreases has been proven to help treat the symptoms of diabetes, but this technique relies upon donations, of which there is not a consistent supply. There is also a risk of transplanting infected or contaminated cells. The new technology could provide a readily available and renewable bank of clean cells for treatment when the patient needed it.
The scientists say that there is a long way to go before this can be taken into humans. There are safety issues still apparent as some of the mice in the study developed tumours, called 'teratomas'. Some critics are also concerned with whether the transplanted hESC derived cells would be destroyed by the recipient's body, just as their own original beta cells were.Experts, however, are in no doubt that this is an exciting advancement. 'This for the first time validates that you can use human embryonic stem cells to produce fully functional human islets', says Dr Baetge.