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Inherited Disorders and Birth Defects

Mosaicism 45/46xy



I found out by mishap that my son was karyotype 45x/46xy in utero. He is 7 years old now and is a normal boy. I was told at genetic counseling when he was born, that all I could do was to wait and watch what happens at puberty. My question is, has medicine changed and should we be sitting back watching and waiting or should we be seeing a endocrinologist now? He is normal stature. We see nothing out of the ordinary. We have kept this a secret from everyone because we didn`t want anyone seeing him as different. I often wonder if we should be doing something. At birth they checked his blood and the karyotype was confirmed. They also sent away tissue from his foreskin but the sample was not useable. So we don`t know where the cells with the abnormal karyotype are. Thanks for your response.


As you know, chromosomal mosaicism is when a person has two or more cell lines with different chromosomal constitutions. This usually happens shortly after conception as the cells are dividing. Different tissues of the body may have different proportions of the normal number of chromosomes and abnormal number of chromosomes. In your son's case, he has some cells that have 46 chromosomes (44 autosomes (non-sex chromosomes) and 2 sex chromosomes - an X and a Y AND some cells that have 45 chromosomes (44 autosomes and 1 sex chromosome - an X chromosome). So he is missing the Y chromosome in some of the cells in his body. As you mention, you do not

When this finding is diagnosed prenatally (you situation), the baby is reported to be a normal male in more than 90% cases. In the small number of cases that have problems associated with this type of chromosomal finding - the baby may have other problems such as short stature or abnormalities of the genitalia.

We would expect your son to continue to grow and develop normally as he is doing now. The only other problems that sometime occur are the possibility of the testes developing a cancer and infertility. Some males with 45X/46XY have been found to be infertile. However, you cannot evaluate this until puberty.

If you are concerned, you should talk to your doctor about these issues.

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Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University