Chromosomal disorders can cause a range of health problems, from mild to severe. Down syndrome is a well-known disorder caused by an extra copy of chromosome 21, while missing or extra sex chromosomes can cause Turner or Klinefelter syndrome. Chromosome testing during pregnancy is recommended, but even with a diagnosis, it can be difficult to predict the severity of the disorder. Some chromosomal errors have no impact on a child’s life.
When the egg and sperm or sex cells first meet at the moment of conception, there is a meeting of the chromosomes that will help determine almost all things about a growing baby. Ideally this match works well, but sometimes mistakes happen and people get extra, deleted, or partially missing chromosomes. This can cause a variety of chromosomal disorders, many of which are so severe that the pregnancy ends in miscarriage. Unless miscarriages have been frequent, parents may never know that a lost child had chromosomal problems because it is not something that is usually evaluated. In other circumstances, chromosomal disorders do not cause death, but they can have a greater or lesser impact on a child’s life and health.
There are some well-known chromosomal disorders such as those involving the inheritance of a third copy of a chromosome. The best known of these is Down syndrome, also known as trisomy 21. It describes a state in which children obtain three copies instead of two of chromosome 21, resulting in a variety of conditions that can differ in the degree of expression. Some symptoms of this condition include mild to moderate retardation, facial expression changes, and an increased risk of congenital heart defects or disease. To confuse matters, some people have mosaic Down syndrome, in which only some cells possess the third chromosome, and this can change Down’s expression a lot or a little.
Unlike Down syndrome, there are chromosomal disorders in which an additional sex chromosome, such as the X or Y, is inherited, or in which part of a sex chromosome is missing. Missing sex chromosomes could cause chromosomal disorders such as Turner syndrome in girls, which causes infertility, slow growth, failure to reach puberty, and potential other organ defects. If caught early, this condition can be treated with things like hormones to help growth and achieve natural maturation. Conversely, women can inherit a third X, which may not be noticeable because it causes very few symptoms.
When guys get a second or third X, the result isn’t quite as good. Boys can develop Klinefelter syndrome, which can cause infertility or low levels of male hormones in adulthood. This could be treated with male hormones. There can be a number of other problems with the X or Y chromosomes, each of which results in chromosomal disorders.
Additional disorders could result from partially missing, completely missing, or malformed or inverted chromosomes. The conditions that could result depend on the number of chromosomes and sometimes there is no “disorder” associated with some chromosomal errors. People are usually advised by their doctors, especially if they are over 35, to have chromosome analysis or testing while a baby is in utero. There are some risks in testing, but also in not knowing. It is an issue that must be weighed carefully by every family.
Another important thing to note is that even with chromosomal disorders diagnosed, it is usually difficult to tell how severe the expression of that disorder will be. Some conditions such as trisomy 18 have a fairly predictable rate of decline, tending to cause death soon after a baby is born. It may be much more difficult to predict the degree of problems or function a child with other types of disorders, such as trisomy 21 (Down), will have.
This aspect of chromosome malfunction remains mysterious in many cases, making it difficult for parents to get a strong sense of what life might be like with a child who has chromosomal disorders. Additionally, there are many chromosomal errors with little or no expression. A mistake can simply be a mistake that has no impact on a child’s life.
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