Understanding Chromosomal Abnormalities

Understanding Chromosomal Abnormalities

If your child has a chromosomal abnormality, you’ve probably been given a crash course from a geneticist on what it means. Below are some simplified information to review types of chromosomal abnormalities and aberrations and what it all means. Please comment below and share your experience with us, or give us a feedback about this article. If you think some tips are not included here, please let us know so that we could share them with the rest.

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- Chromosomes are located in the nucleus (command center) of a cell. They are thread-like structures that hold DNA. DNA carries genetic information and instructions that tell the body what to do.

- Genes are made up of sections of DNA, and so they also carry genetic information. Genes carry info that determines a person’s characteristics, such as what they look like and health conditions they might be prone to, such as cystic fibrosis. So, chunks of DNA make up genes, and genes are located on structures called chromosomes.

- Typical human beings have 23 pairs of chromosomes. One copy of each chromosome comes from each parent, for a total of 46 individual chromosomes. Why don’t we just say 23? Because the two chromosomes are slightly different from each other because one chromosome comes from mom and one comes from dad. Think of it as a inheriting a pair of socks from your parents – one is mom’s, one is dad’s. They’re both socks but they have slightly different properties – like different colors or sizes or materials – but they work together as a pair. That pair of socks, or chromosomes, contain the genetic information for a child. This is why a child inherits some traits from each parent.

- Each chromosome has a point which divides it into two sections, or “arms” of different lengths. The short arm is called the “P” arm and the long is called the “Q” arm. That’s why geneticists identify abnormalities with the letter, telling you, for example, your child has an abnormality on Chromosome 8P – meaning the short arm of chromosome 8, or an abnormality on 7Q, the long arm of chromosome 7.

- During reproduction, a sperm fertilizes an egg. Sperm and egg both contain genetic information in the form of chromosomes, and the chromosomes combine, one from each parent, to form the DNA of the child. The fertilized egg begins to copy itself into new cells, duplicating the chromosomes for every new cell. Sometimes the chromosomes don’t copy correctly or were not formed correctly and this can lead to problems. Some chromosomal abnormalities lead to miscarriage, some may cause various diseases, disorders or disabilities and some have no known effect at all.

- Inversion: Sometimes a section of a chromosome is flipped upside down. That’s called an inversion, and it’s actually fairly common in the general population, but most people don’t know they have it because it doesn’t usually have an effect.

- Duplication: Sometimes part of a chromosome gets copied twice and so a chromosome ends up longer than it should be because it has as extra copy of one section. The chromosome will have twice as many of some genes as it should. That’s called a duplication. The effects of duplication can vary widely, depending on the genes copied.

- Deletion: Sometimes a section of the chromosome gets left out, often from the ends of a chromosome, and means the chromosome is shorter than it should be. This is called a deletion. This also has a huge variety in how significant the effects can be, depending on what genes are omitted.

- Trisomy: Sometimes a baby inherits two chromosomes from one parent, instead of just one. This is called a trisomy because the child ends up with three chromosomes. Down syndrome and Klinefelter syndrome both result from a trisomy.

- Missing chromosome: Sometimes a child doesn’t receive both chromosomes and one is left out or is only partially copied. This can result in Turner Syndrome, for example, when a child receives only one X chromosome and the other sex chromosome is absent.

- Mosaicism: Sometimes a person has a mixture of cells containing two different sets of genetic information. This is called mosaicism. It can have a variety of effects on a person, from causing mild, moderate or significant problems to having no effect at all. It could also lead to harmless effects, such as people who have eyes of two different colors. In fact, all typical women have mosaicism. Typical women have two X chromosomes and typical men have an X and a Y chromosome. One chromosome comes from each parent. Only one copy of the X chromosome is needed for a cell to function, so one copy gets turned off in each cell. Each cell randomly chooses which copy to turn off, so cells could have either X chromosome functioning. In women with “normal” chromosomes, this mosaicism has no detrimental effect.

- Diagnosis: Some chromosomal abnormalities are fairly common and can be easily diagnosed through prenatal testing. Some cells from the fetus cross over into the mother’s blood stream during pregnancy, so some abnormalities can be detected just by testing the mother’s blood. As of now, other abnormalities cannot be diagnosed prenatally except by amniocentesis or chorionic villus sampling (CVS). Both of these procedures are invasive and involve some risk of miscarriage. After birth, chromosomal abnormalities can be diagnosed by blood test, and analysis can be fairly simple to very detailed. Some insurance companies do not cover genetic testing in the U.S. and it can be very expensive. If your insurance won’t cover it, inform your doctor and ask them to help you negotiate a price with the lab. They will often help you and give you a discounted rate.

- The genetic code is important, but is by no means the only thing that determines a person’s abilities, health or long-term outlook. Environment is hugely important. For instance, some people are genetically more prone to certain health problems, but we know that health can be vastly changed by lifestyle factors. Two people with the same genetic problem might have very different outcomes based on their diet and exercise, for example. The same is true of people with chromosomal abnormalities. Interventions such as therapies, alternative education techniques and growing up in a home that is loving, interactive and supportive can have profound effects on a person’s outcome.

- The scientists involved with the Human Genome Project have estimated that humans have between 20,000-25,000 genes. Scientists are working to figure out what individual genes do and building a database, but as of now, scientists do not know what most of them do. There is also a lot of “junk DNA” that scientists think is probably obsolete genetic material that no longer has a purpose and doesn’t actually do anything. Some genes do the exact same thing as other genes. If some of those genes are deleted or duplicated, does it really make that big of a difference? They don’t know – no one does.

- Genetics is a very new field and there is ton that doctors and scientists do not know. Diagnosing chromosomal abnormalities is still new and there has been hardly any study of most of the rare abnormalities. Even then, there is a huge variation among how much an abnormality will affect a person. There are many, many cases of doctors saying all the things a person with chromosomal abnormalities will never do – and that person proving all the “experts” wrong. My child has a rare abnormality and she is already doing more than doctors said she would, and I’ve met many other families who say the same. When a doctor tries to tell you all the limits a person with an abnormality will have, take it with a grain of salt. They can’t predict the future and they truly don’t know.

- Chromosomal abnormalities are natural and happen by chance. A parent has absolutely no control over it and abnormalities can occur in the sperm or the egg. No parent is ever “to blame” for an abnormality. Sometimes a parent can unwittingly pass on an abnormal genetic trait from their own DNA, and sometimes, abnormalities just randomly happen. Typically, a greater number of abnormalities occur in older parents, but any parent of any age can (and will) produce at least some abnormal sperm and eggs. Many of these abnormalities will result in miscarriage, but some will result in a child who is a little different.

- DNA is made up of four chemical bases, adenine, thymine, guanine and cytosine – A, T, G, C for short. The way these bases are arranged on the DNA determines genetic information. Humans with typical chromosomes have billions of sets of DNA bases and 99 percent of them are identical to the DNA of every other human. However, scientists are estimating that there is variety in about 1.4 million DNA bases among humans. That means there is a great deal of variety among humans. There really is no “normal”.

- Human evolution has come about as a result of genetic mutations – slight changes – to DNA. That means that we would never have evolved to become human beings without the people who are genetically a little different from the rest – the ones with the “abnormalities”. The only reason we’re not singled-celled amoebas is due to genetic abnormality. We owe our very existence to people with genetic abnormalities. Abnormalities are natural - they have a purpose. Abnormalities make beautiful people.

- If you or a loved one has a chromosomal abnormality, here is a final thought. The flowers, orchids, have a phenomenal amount of diversity among them and are some of the most highly evolved plants in the world. Natural orchid reproduction can be very slow so commercial orchid producers rely almost entirely upon genetic manipulation and fertilization. Orchid growers are always trying to produce new hybrid breeds that are unlike anything anyone has seen before, and the way they get those new breeds are to alter an orchid’s genetics to produce abnormalities in the chromosomes. The new hybrid orchids that are produced are truly unique, one-of-a-kind flowers. They are prized worldwide for their beauty and rarity, and they are so special precisely because they have abnormal chromosomes.

Please comment below and share your experience with us, or give us a feedback about this article. If you think some tips are not included here, please let us know so that we could share them with the rest.