Sex differences in reproductive fitness contribute to preferential maternal transmission of 22q11.2 deletions

22q11.2 deletion syndrome (22q11.2DS) is one of the most common  genetic syndromes in humans. For the first time in history, most with  22q11.2DS are living to adulthood, and there is a 1 in 2 chance of  passing on the condition to a child. We compared the number of children born to adults with 22q11.2DS with the number born to their brothers and sisters without 22q11.2DS. Few with 22q11.2DS have children, apparently not related to heart defects but possibly because they find it hard to meet a partner. Those who do are more often women. There is a subgroup of women with 22q11.2DS who have about as many children as their sisters. This may be why more inherited cases are from a mother than a father. We also observed that men with 22q11.2DS are more likely to pass on the condition to their sons than daughters. (By Dr Anne S Bassett, http://jmg.bmj.com/content/early/2011/11/02/jmedgenet-2011-100440.abstract?papetoc )