Risk of mental defects at birth

Recent research suggests that families who have a child with Down's syndrome appear to have a higher-than-average risk of having another child with neural tube defects and vice versa. Neural tube defects (NTD), such as spina bifida, are a type of birth defect affecting the brain and the spine. Down's syndrome is the most common genetic cause of mild to moderate mental impairment, and occurs in about 1 in 800 live births. Most cases of Down's syndrome occur when chromosomes fail to separate properly during cell division, resulting in an extra chromosome being transmitted to one of the resulting cells. Folate is responsible for certain changes that enable the chromosomes to separate properly, and previous research has suggested that Down's syndrome risk increases in mothers who do not properly metabolise folate. In the study, researchers from the Tel Aviv University in Israel reviewed the medical history of children born to families at risk of having children with Down's syndrome or neural tube defects. They studied two series of families using information obtained from medical records about maternal age, pregnancy outcome and congenital malformations. The first were 493 families from Israel who were at high risk of NTD and the second, 516 families from Ukraine at high risk of Down's syndrome. All of the families featured in the study had one pregnancy that had resulted in either a neural tube defect or Down's syndrome and at least one other pregnancy. It was found that among the 493 families studied in Israel with one pregnancy resulting in a neural tube defect or hydrocephalus, 11 of their 1,492 other pregnancies resulted in Down's syndrome. Among the 516 Ukrainian families with a pregnancy resulting in Down's syndrome, seven of the 1,847 other children had a neural tube defect, a rate that is slightly higher than that seen in the general population. The risk of Down's syndrome increases with the age of the mother. The researchers noted that the rate of Down's syndrome in the families studied, however, was five times higher than one would expect from mothers of similar ages.

Research has shown that low folate levels in the mother may result in neural tube defects, and that taking folic acid can prevent such problems. The researchers suggest that some cases of Down's syndrome may also result from low folate, and supplements of folic acid may also help prevent Down's syndrome in babies whose family history includes a risk of neural tube defects. However, they and other experts caution that more research is needed before folic acid is recommended as a routine to prevent Down's syndrome in families at risk.

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