Introduction
With today's technical possibilities various chromosomal aberrations can already be determined before birth.
Prenatal examination
In order to reduce the risk of the birth of a severely handicapped child, by means of amniocentesis or a chorionic villus biopsy during early pregnancy, the future mother can have the chromosome set of the embryo examined for chromosomal aberrations.
Sometimes, chromosomal aberrations can also be suspected in the 1st ultrasound examination based on a neck edema.
A neck edema (red arrow) corresponds to a collection of fluid that is present temporarily between the 11th and 14th week of pregnancy and can indicate a chromosomal aberration.
Fig. 24If there is evidence of an increased incidence of congenital abnormalities, monogenetic hereditary diseases or habitual abortions in the anamnesis, genetic counseling should by all means be offered.
The most recent examinations of ultrasound images made between the 11th and 14th weeks of gestation have shown that the nasal bone is visible in profile in 99.5% of the fetuses without chromosomal aberrations, whereas it is missing in 73% of the fetuses with trisomy 21
Clinical picture
Children with a deviating number or structure of chromosomes mostly have multiple abnormalities, often associated with mental retardation, or are in general unable to live. In the clinic a chromosome analysis is indicated when the following criteria are present in a patient and other pathogenic causes have been eliminated:
- Pre- and postnatal growth disorders
- Mental retardation
- Abnormalities
- Dysmorphism signs
Examples of such diseases are:
- Down syndrome or trisomy 21 (an additional chromosome 21). These children are mentally retarded, have typical somatic symptoms and frequently a cardiac defect.
- Trisomy 13 or 18. These children have multiple abnormalities that are mostly lethal.