14. Turner syndrome.
| a. | is associated with 47 XXX | False |
| b. | 98% of affected pregnancies will fail to reach term | True |
| c. | is present in about 1% of conceptions | True |
| d. | may be suspected on scan evidence of cystic hygroma | True |
| e. | removal of gonads is advocated if a mosaic involving 46XY exists | True |
| f. | ~ 10% of neonates with Turner syndrome have heart defects | True |
The key facts you need for the DRCOG were covered in MCQ 4, question 24.
For further information see the Turner Syndrome Support Society.
Turner syndrome is usually 45XO.
In ~ 80% of cases it is due due to loss of a paternal X or Y chromosome during sperm manufacture- MRCOG stuff.
For the addict to the really small print, it means these girls could get an X-linked recessive disorder.
This could lead to a tricky MRCOG MCQ!
"X-linked recessive disorders only occur in the male."
Such conditions are Fragile X syndrome, haemophilia (MCQ11, question 11) etc.
A girl with an affected gene would normally be protected by having a normal gene in her other X chromosome.
Unlike her brother: he only has one X chromosome, so an affected gene would give him the disease.
The girl with Turner is in the same boat, so would have the disease if her X chromosome was affected.
Turner syndrome may be associated with mosaicism, in which different cells lines exist e.g. 45XO with 46XX or 46XY.
In the rare cases that there is some Y material and gonadal malignancy is quoted as occurring in 20%.
Gonadal malignancy is not a feature except in this rare situation.
About 1% of conceptions are believed to result in Turner syndrome, but the incidence at birth is only 1: 2,500.
The vast majority miscarry in the first trimester.
47XXX occurs in about 1:1000 births (See MCQ 4, question 37).
There is usually intellectual impairment but not severe handicap.
And a tendency to behavioural abnormalities, e.g. shyness and poor social development.
The diagnosis is not usually made in childhood as physical development is normal.
Most are fertile, but about 25% show ovarian dysfunction with early menopause, oligomenorrhoea and infertility.
Cystic hygroma, (see MCQ10, question 36) is a marker for Turner syndrome.
About 50% of cystic hygromas diagnosed on ultrasound will be linked to Turner syndrome.
Another 10 - 15% will be due to chromosomal abnormalities such as T13, T18 and T21.
Congenital heart defects occur in 10-15% of neonates with Turner syndrome, c.f. 0.8% of neonates overall.
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