Turner syndrome
Turner syndrome occurs when one of the two X chromosomes that are found in females is completely or partially missing. It therefore only occurs in females. The process tends to occur randomly (can be either from the father or the mother) and does not predict additional risk in future siblings.
This may seem odd as you will be aware of the process of X-inactivation (Lyonization) whereby one X chromosome is inactivated in each cell. This might lead you to suspect that having only one X chromosome is okay. The reason having just one X chromosome is an issue is that in X-inactivation not all genes are inactivated in the inactivated X chromosome.
Features include:-
Girls with Turner syndrome typically have a reasonably normal intelligence (mean full scale IQ of 90), however, they may have difficulty with nonverbal, social, and psychomotor skills.
This may seem odd as you will be aware of the process of X-inactivation (Lyonization) whereby one X chromosome is inactivated in each cell. This might lead you to suspect that having only one X chromosome is okay. The reason having just one X chromosome is an issue is that in X-inactivation not all genes are inactivated in the inactivated X chromosome.
Features include:-
- Short stature
- Webbed neck
- Broad chest (widely spaced nipples)
- Gonadal dysfunction (amenorrhoea and infertility)
- Congenital heart disease (cardiac malformation in approx 1/3 of cases)
- Hypothyroidism
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Girls with Turner syndrome typically have a reasonably normal intelligence (mean full scale IQ of 90), however, they may have difficulty with nonverbal, social, and psychomotor skills.
