NEW YORK (Reuters Health) - Paternal age is directly related to the risk of Down's syndrome when maternal age is 35 years or older, according to a report published in the June issue of The Journal of Urology.

The effect of maternal age on the risk of Down's syndrome is well established. In contrast, relatively little is known about the impact of advanced paternal age, Dr. Harry Fisch, from Columbia-Presbyterian Medical Center in New York, and colleagues, note.

To investigate the effect of paternal age on Down's syndrome risk, Dr. Fisch's team analyzed data from the New York State Department of Health birth defect registry from 1983 to 1997.

During the study period, a dramatic rise in the number of children born to parents who were both 35 years of age or older occurred, the authors note. The number of older mothers and fathers increased by 111% and 60%, respectively.

When mothers were younger than 35 years, paternal age had no effect on Down's syndrome risk, the researchers report. With older mothers, however, fathers who were at least 40 years of age were twice as likely as men 24 years or younger to have a child with Down's syndrome.

The highest risk of Down's syndrome occurred when both mother and father were 40 years of age or older. In this setting, the rate of the genetic disorder was 632 cases per 100,000 births.

Exactly how maternal and paternal factors work together to increase the risk of Down's syndrome is unclear, the authors note. In terms of paternal factors, it may be that sperm from older men are more likely to contribute an extra chromosome than sperm from younger men. As for maternal factors, advanced age may impair the ability to recognize and abort a chromosomally abnormal fetus.

The current findings may also have implications beyond Down's syndrome, Dr. Fisch's team states. "The adverse effect of advanced paternal age on Down's syndrome may represent a paradigm for other genetic abnormalities in children of older fathers that must be addressed in future studies."

J Urol. 2003 Jun;169(6):2275-8

Copyright © 2003 Reuters Limited. All rights reserved. Republication or redistribution of Reuters Limited content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters Limited. Reuters Limited shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon.