Chromosomes are long, continuous molecules of DNA and protein. This is the specific form that genetic material takes in living things in the stage before mitosis (cell division).
Humans normally have 23 pairs of chromosomes in each cell. Twenty-two pairs are called autosomes and one pair made up of the sex chromosomes.
Chromosome abnormalities are diseases caused by abnormal chromosome structure or an abnormal number of chromosomes. for example, when chromosome 21 has three copies instead of two, this is known as Down syndrome. People with three copies of chromosome 18 (instead of two) will have Edwards syndrome.
What causes chromosome abnormalities?
Unlike genetic diseases, chromosome abnormalities are usually not hereditary. Although the chromosome defect is often found in the mother or father’s sex chromosomes, this condition is not hereditary since none of the parents suffer from the disorder themselves.
For example, people with a pair of joint 21 chromosomes in their cells will have children with Down’s syndrome, because one parent passes down two joint copies of this chromosome and the other parent passes on one copy – a total of three copies of chromosome 21 (also known as a trisomy). However, the parents themselves will not have Down syndrome since all their cells have a normal number of 21 chromosomes (two copies).
Similarly, according to one theory explaining the causes of Down syndrome, the reason for the extra chromosome appears to be two copies of chromosome 21 becoming “Stuck” together in aging eggs. If this theory is correct, it can help explain why advanced maternal age is linked to the chances of having a child with Down’s syndrome. It should be noted that in some cases, the chromosome abnormality occurs only after fertilization.
Common chromosome abnormalities
Common chromosome abnormalities include:
Down syndrome – the most common chromosome abnormality, also called trisomy 21. People with Down syndrome have intellectual disabilities, distinct facial features, childish behavior, a short life expectancy, heart defects, infertility and more.
Edwards syndrome – the second most common chromosome abnormality (1 in 5,500 live births). People with Edwards syndrome suffer from intellectual disabilities, a small lower jaw (Micrognathia), anatomical defects in their fingers, heart defects, a cleft palate and more. Around 50% of babies with Edwards syndrome do not live past the first week of their lives, and less than 10% of babies live past one year of age.
Patau syndrome – people with Patau syndrome have three copies of chromosome 13 instead of two in all their cells. Symptoms include spina bifida, polydactyly, kidney defects, abnormalities in the sex organs, severe intellectual disabilities, a cleft palate, umbilical hernia and more.
How are chromosome abnormalities diagnosed?
Common chromosomal abnormalities can be detected during the pregnancy. In cases of IVF, they can be detected in fetal cells.
Chromosome abnormalities are tested by dying the chromosomes and analyzing their number and structure. Fetal DNA segments in the mother blood can be isolated to examine the fetal genetic material during the pregnancy. Other methods that enable examining fetal DNA include CVS (chorionic villus sampling) or amniocentesis.
Chromosome disorders can also be diagnosed at a laboratory after birth. The disorders can also be diagnosed by identifying the unique clinical symptoms associated with each disorder.
What is the treatment for chromosome abnormalities?
Since each chromosomal disorder has different symptoms, treatment methods may vary. It is important to understand that chromosome abnormalities are incurable. Most treatment is based on supportive care. This means treatment is not designed to cure the disorder but reduce symptom severity and lower the risk of complications.
In addition, the goal of treatment is to improve patients’ quality of life. This can include corrective surgery for birth defects, psychiatric medication for mental health issues and behavioral disorders, special education for children with intellectual disabilities, speech therapy, occupational therapy, physiotherapy, animal-assisted therapy, nutritional counselling, and more.
Since there is no known cure for chromosomal disorders, treatment is usually chronic and is needed in all life stages. Medical supervision is important in patients with chromosome abnormalities, to ensure treatment effectiveness.