Definition - What does Monosomy mean?

Monosomy is a chromosomal disorder (aneuploidy) where one chromosome from a pair is missing. Rather than having the normal 46 chromosomes, an affected person has 45 chromosomes. The only viable monosomy is Turner syndrome (TS), which affects the X chromosome and is also called monosomy X. Only females have two X chromosomes, therefore, only females develop this condition. Females with TS lack functional ovaries and cannot ovulate. Thus, infertility is a common problem encountered in females with monosomy.

TS is a common chromosomal abnormality, affecting about 1 out of every 2,500 female live births.

FertilitySmarts explains Monosomy

Normally, a sperm cell (that has 23 pairs of chromosomes) fertilizes an egg (that also contains 23 pairs of chromosomes) so that the resulting embryo will have 46 chromosomes. However, sometimes an error occurs during the formation of a sperm or egg cell causing it to have a sex chromosome that is partially or completely deficient.

Girls with monosomy typically have a short stature, a webbed neck, and a broad chest with widely spaced nipples (due to inadequate development of breasts). Because they lack well-developed ovaries, they never have menstrual periods and cannot conceive naturally.

With individuals suspected of having TS, a genetic test called karyotyping can be done, which helps detect the chromosomal pattern with a missing X chromosome. The karyotype in affected individuals is 45 X. Monosomy can also be diagnosed while a fetus is in the uterus of her pregnant mother by taking a sample from amniotic fluid and analyzing its chromosomal makeup. Additionally, embryos used for assisted methods of pregnancy can be screened for monosomy via preimplantation genetic diagnosis (PGD), in which cells from the embryo are removed and examined for any chromosomal abnormality. PGD allows selective transfer of only normal embryos.

Hormonal replacement therapy is required to induce puberty and menses in females with monosomy. These women can get pregnant using egg donation; the results are excellent with 46% of embryo transfers leading to a successful pregnancy. The affected women, however, are prone to some risks and require a careful follow-up and monitoring. On the contrary, children born to women with TS following egg donation carry no additional risks.

Share this: