My daughter is a XXX -- that is, she has an extra X chromosome. She is 18 years old, of normal intelligence, tall, loosejointed but well-proportioned. She has miscarried twice in the last six months. Could this be related to her chromosomes?

Pat

Women with a triple-X sex chromosome abnormality may be fertile. While there appears to be an increased risk of a miscarriage or a genetically abnormal child, the extent of this risk has not yet been defined.

Studies of fertile 47XXX women showed, surprisingly, a low incidence of chromosomal anomalies in their babies. To explain this, some scientists have theorized that fertile triple-X women may produce normal eggs by the way their cells divide during the process of egg formation. In women with normal chromosomes, a 46-chromosome cell would split into two germ cells (the beginnings of eggs), each of them 23X (23 chromosomes with one X chromosome). In a triple-X woman, a single 47XXX cell could split to form a normal 23X germ cell and an abnormal 24XX germ cell. The abnormal 24XX will likely die off, while the 23X will go on to form a normal egg.

Women with the mosaic pattern 46XX/47XXX -- in which some cells contain a normal chromosomal makeup and others are abnormal -- seem to have a somewhat higher risk of bearing chromosomally abnormal offspring or miscarrying. This may reflect a tendency to form abnormal egg cells, with an extra X or no X chromosome at all.

As your daughter has already had two miscarriages, this may indicate that she has a mosaic pattern. I would recommend a consultation with a genetic counselor who could better tell her the odds of successful pregnancy with her condition. It would be most helpful to examine the chromosomes from any pregnancy loss that she would incur to see if that explains the loss.