All living beings are made out of cells and inside those cells there is an area which contains all necessary information for that organism to work properly. In humans, this information is called DNA which is located inside a structure called the nucleus.
Inside the nucleus DNA usually looks like a bunch of threads, however, during certain points in the life of a cell (mitosis), these threads are organized in the form of sticks with a division in the middle, also known as chromosomes. Humans have a total of 46 chromosomes in most of their cells, 44 autosomal and 2 sexual (XX or XY). Since they come in pairs (2 similar copies of the same chromosome), experts usually refer to them by their pair number (so, chromosome # 1 refers to not one but 2 chromosomes and so on). Their number and structure needs to be carefully regulated to avoid situations as the ones we’ll be discussing in this article.
There are 2 main types of rare chromosomal abnormalities: Numerical, which are characterized by an excess or lack of entire chromosomes. A common example is having 3 instead of 2 chromosomes #21, a condition also known as Down syndrome. Structural abnormalities are more varied and are characterized by some form of physical alteration (missing parts, extra copies of some segments of DNA, being fused with other chromosomes, etc). Among all rare chromosome disorders, some are more frequent than others. Down syndrome is by far the most common with a 0.5 to 1% incidence, but there are others more rare, like Miller-Dieker syndrome or Jacobsen syndrome which either have an extremely low incidence (0.00001%) or their statistics are simply unknown. However, some even rarer disorders do exist, these are so unusual to see that frequently don’t have names, only descriptive technical codes like “Duplication (9)(p22pter) with Deletion (11)(q23.3qter)”. As technology becomes more advanced, our capacity to detect these rare disorders grows. Nowadays we know more about these disorders than ever before.
How does Rare Chromosome Disorders take place?
The precise mechanisms behind these disorders are not well-understood, not even in the case of Down syndrome. For now all we know is when they happen, when cells divide (mitosis). During mitosis DNA needs to be organized as chromosomes and is in this point where errors can occur.
When germline cells (eggs or sperm) experience these errors, children born from these cells will have them in every cell of their bodies. When they happen in any other type of cell, then the effects will be less extensive. Among potential consequences we found: infertility, cancer, incompatibility between tissues, etc. Certain factors can increase the probability for the appearance of chromosomal abnormalities. For example, women of a certain age are more likely to have children with these disorders and exposure to mutagens can also have this effect in both male and females.
What are the Symptoms?
Since we are discussing a group of rare conditions, naturally, each one will have its own set of symptoms, however, author do report some common trends:
Although these conditions tend to cause problems, some of them allow normal development and average intelligence, like those identified as: 2p, 6p, 6q, 8p, 11q, 18q, 20p and 21q.
Is it Curable?
This is not the kind of disorder you can treat. In some cases, symptoms can be treated to improve quality of life, but most of the time, you’ll have to choose an option from this list:
Counseling: A genetic counselor will explain all the features of your/ your children’s particular disorder, provide information about possible interventions to improve quality of life and determine how likely is the condition to be inherited.
Occupational therapy: This method guides people through a series of daily activities as a form of rehabilitation or treatment to deal with physical or mental disabilities.
Physical therapy: This can help by developing strength and improving coordination.
Medication: Because of the nature of some rare conditions, medications may be needed due to some associated condition like cardiovascular disease, the exact medication/ medication recommended will vary with with each case.
Which Doctor should be Consulted for it?
Most of these conditions become apparent during infancy, therefore, for those cases we recommend seeing a pediatrician with experience dealing with chromosomal disorders. Genetic counselors should also be consulted.
For specific conditions associated with chromosome disorders, other specialists can be consulted: Cardiologists, endocrinologists, pneumonologists, etc. Rare chromosomal conditions do affect a certain percentage of the population, however, their management is generally similar to many other of these disorders.