Learn how and why chromosomal abnormalities occur (2023)

A chromosomal abnormality occurs when a fetus has the wrong number of chromosomes, the wrong amount of DNA within a chromosome, or structurally defective chromosomes. These abnormalities can result in the development of birth defects, disorders such as Down syndrome, or possibly miscarriage.

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Understanding genes and chromosomes

Your body is made of cells. At the center of each cell is a nucleus, and within the nucleus are the chromosomes. Chromosomes are important because they contain genes that determine your physical characteristics, your blood type, and even your susceptibility to certain diseases.Each cell in the body normally contains 23 pairs of chromosomes (46 chromosomes total), each of which contains approximately 20,000 to 25,000 genes.

Half of a person's chromosomes come from the egg of one biological parent, and the other half come from the sperm of the other biological parent.

What are chromosomal abnormalities?

Chromosomal abnormalities are differences in chromosomes that can occur during development. They can be "de novo" (unique to the fetus) or inherited from one parent. Anomalies are divided into two categories: numerical and structural.

numerical anomalies

Numeric refers to having a different number of chromosomes than expected; it can be more or less. This is also calledaneuploidy. Each scenario has a specific term:

(Video) What are chromosome abnormalities? A simple to understand guide

  • monosomy: One pair is missing a chromosome.
  • trisomy: There are three instead of two chromosomes.

structural abnormalities

When there is a problem with the composition of the chromosome, it is called a structural abnormality. There are several ways in which structural abnormalities can occur.

  • translocation: A part of a chromosome is transferred to another. (This can be a Robertsonian translocation, in which one chromosome is attached to another, or a reciprocal translocation, in which two chromosomes are swapped.)
  • elimination: There is a deleted or missing part of a chromosome.
  • duplication: a chromosome is copied, creating additional genetic material.
  • Ring: A ring/circle is formed when part of a chromosome breaks.
  • investment: a piece of chromosome breaks off and flips over, only to later reconnect to the original structure.

Why do chromosome abnormalities occur?

Chromosomal abnormalities occur because cell division does not proceed as planned. Typical cell division occurs by mitosis or meiosis.

When a cell with 46 chromosomes divides into two cells, this is called mitosis. The new cells must also have 46 chromosomes each. The human body is made up of cells formed by mitosis. During meiosis, a cell also divides into two halves, but each of these halves has 23 chromosomes. Meiosis produces sperm and eggs in the reproductive organs.

If mitosis or meiosis results in a different number of chromosomes than expected, this is considered a chromosome disorder.

risk factor's

There are a few factors that can potentially increase the chance of a chromosome disorder. One of those considerations is the age of the parents.

Women older than 35 years are at higher risk of developing a chromosomal abnormality.While there is conflicting research and more to learn about advanced paternal age (sometimes defined as 40 years or older), there is evidence of a possible increased risk of chromosomal abnormalities.

Additionally, environmental factors, such as fetal drug exposure, may also be involved in chromosomal abnormalities.

chromosome disorders

There are different types of disorders that can result from abnormal chromosomes. The following list is not exhaustive, but includes the conditions that give the fetus the best chance of surviving until birth.

Down syndrome

One of the best-known chromosome disorders is Down syndrome (also known as trisomy 21), which is caused by an extra copy of chromosome 21. Some of the common features of Down syndrome are developmental delay, short stature, slanting eyes top, low muscle tone and a deep crease in the center of the palm.

(Video) Chromosomal abnormalities

The causes of Down syndrome aren't entirely clear, but scientists have discovered a common link between them, among other things.older maternal ageand trisomy 21. The risk has been shown to increase exponentially as a woman ages, from 1 in 1,500 at age 20 to 1 in 50 at age 43.

One in 700 babies in the United States is born with Down syndrome.

turner syndrome

Turner syndrome (also known as gonadal dysgenesis), which only affects women, develops when one of the X chromosomes is completely or partially missing. This could make you infertile or shorter than average. Other features of the condition may include swelling of the feet/hands, excess skin on the neck, kidney and heart problems, and skeletal abnormalities. Turner syndrome can also lead to miscarriage or stillbirth.

Klinefelter syndrome

Klinefelter syndrome, also known as XXY syndrome, is the result of an extra X chromosome in males. It is associated with high rates of sterility and sexual dysfunction. It usually goes unnoticed until puberty, when it is characterized by weak muscles, tall stature, little body hair, and small genitalia.

trisomy 13

trisomy 13oPatau syndrome, is caused by an extra copy of chromosome 13. The syndrome can cause severe intellectual disability, as well as heart defects, underdeveloped eyes, extra fingers or toes, cleft lip, and brain or spinal cord abnormalities. Patau syndrome occurs in one in every 16,000 births, and babies usually die within the first days or weeks of life.

trisomy 18

Trisomy 18, sometimes called Edwards syndrome, is caused by an extra copy of chromosome 18. The syndrome occurs in one in 5,000 live births. Edwards syndrome is characterized by low birth weight, a small and abnormally shaped head, and other life-threatening organ defects. Edwards syndrome is not treated and is usually fatal before birth or within the first year of life.

Triple X Syndrome

Also known as trisomy X or XXX syndrome, triple X syndrome (where there are three copies of the X chromosome) only affects females. The chromosome abnormality can make them taller than average, have weaker muscles, cause speech problems, or experience coordination problems.

Triple X syndrome affects 1 in 1,000 women.

(Video) Pathophysiology 16 Chromosomal abnormalities

XYY syndrome

XYY syndrome affects 1 in 1,000 men and is caused by the presence of an extra Y chromosome. The symptoms of XYY syndrome vary, but men with this disorder may be taller than average, have speech processing disorders, or have difficulty coordinating. It can also cause behavior problems, hand tremors, and weaker muscles.

fragile X syndrome

Fragile X syndrome or Martin Bell syndrome results from a genetic mutation on the X chromosome. It can cause mental and learning disabilities, social/behavioral problems, and developmental delays.

Cri-Du-Chat Syndrome

If a part of chromosome 5 is missing, it is classified as cri du chat (crying cat) syndrome or 5p (minus 5p) syndrome. The abnormality is so named because babies who have it can cry like a cat. Symptoms of cri-du-chat can include a small head, poor muscle tone (in babies), failure to thrive, low birth weight, heart defects, or intellectual disability.

pregnancy complications

Chromosomal abnormalities can cause complications during pregnancy. Two of these complications are spontaneous abortions and molar pregnancies.

spontaneous abortion

Chromosomal abnormalities are one of the mainCauses of spontaneous abortionsduring the first trimester. In an early miscarriage, chromosomal defects can prevent an embryo from developing normally. When this happens, the expectant mother's immune system may respond by spontaneously terminating the pregnancy, although some miscarriages still require medical or surgical assistance to allow the tissue to exit the uterus.

Research suggests that chromosomal abnormalities account for 50% or more of first-time miscarriages. In most cases, the error is a random abnormality and the person will have a healthy pregnancy later.

mill pregnancy

In other cases, a chromosome abnormality can lead to a rare condition calledmolar pregnancy. During a molar pregnancy, the tissues that are supposed to form a fetus develop into an abnormal growth in the uterus. There are two types of molar pregnancies:

(Video) CHROMOSOME ABNORMALITIES presented by Psychology Professor Bruce Hinrichs (Scientific Psychology)

  • complete molar pregnancy: A complete molar pregnancy occurs when the egg contains no genetic information and is fertilized by one or two sperm. Due to the lack of genetic information from the mother, the fertilized egg develops a placenta that looks like a bunch of grapes without an accompanying fetus.
  • Partial molar pregnancy: A partial molar pregnancy occurs when an egg containing genetic material is fertilized by two sperm. It causes the development of an embryo that has multiple copies of chromosomes, forms abnormal placental tissue, and usually does not survive.

Understanding abortion statistics

chromosome test

Fetal chromosome testing, while not routine, is available to expectant parents who choose to have it done. These tests include screening and diagnostic tests.

At the end of the first trimester, you may choose to have a screening test, which will give you and your doctor an idea of ​​how likely it is that your baby has a chromosome abnormality. These tests cannot diagnose a chromosome abnormality. Screening tests include ultrasound and blood tests such as B. A panel of biomarkers or tests for circulating placental DNA.

Although screening tests cannot diagnose a chromosome abnormality, there are tests that can. diagnostic tests such aschorionzote biopsymiAmniocentesisthey are more invasive but can diagnose abnormalities that previous screening tests may have indicated.

A word from Verywell

Learning about chromosome abnormalities can be overwhelming. While there are tests that can be done during the first trimester to provide information about development or complications, preconception genetic counseling can also offer more valuable information for anyone trying to have a baby.

High-Risk Pregnancy Overview


What makes you high risk for chromosomal abnormalities? ›

Risk factors include older age in the woman, a family history of genetic abnormalities, a previous baby with a birth defect or miscarriage, and a chromosomal abnormality in one of the prospective parents.

Can you prevent chromosomal abnormalities in pregnancy? ›

The risk can be lowered by: Seeking medical care three months before becoming pregnant to discuss health problems and medicine use. Taking a daily prenatal vitamin that contains 400 micrograms of folic acid for three months before becoming pregnant.

Can you fix chromosomal abnormalities How? ›

In many cases, there is no treatment or cure for chromosomal abnormalities. However, genetic counseling, occupational therapy, physical therapy and medicines may be recommended.

What is the study of chromosomes and their abnormalities called? ›

Cytogenetics is the study of chromosomes and their role in heredity.

Can you prevent chromosomal abnormalities? ›

Taking a daily prenatal vitamin that includes at least 400 micrograms of folic acid can help prevent a variety of birth defects. You should be taking prenatal vitamins if you're of reproductive age, when you're actively trying to conceive and/or as soon as you find out you are pregnant.

How can you prevent miscarriage due to chromosomal abnormalities? ›

To avoid pregnancy with chromosomal abnormalities we recommend that Preimplantation Genetic Screening (PGS) be performed. PGS from IGENOMIX is an early genetic diagnosis of the embryo prior to its transfer to the uterus, and therefore prior to establishment of pregnancy.

What makes a woman high risk for chromosomal abnormalities? ›

These women are at increased risk: Maternal age of 35 or older at delivery. Family member or previous pregnancy with a chromosomal abnormality. Abnormality seen on ultrasound.

Do chromosomal abnormalities come from mother or father? ›

Although it is possible to inherit some types of chromosomal abnormalities, most chromosomal disorders (such as Down syndrome and Turner syndrome) are not passed from one generation to the next. Some chromosomal conditions are caused by changes in the number of chromosomes.

What Week Do miscarriages due to chromosomal abnormalities occur? ›

Even the chromosomal abnormalities that are viable, such as monosomy X and trisomy 21, are often lost during the first twelve weeks after conception. JTs were first described in miscarriages by Jacobs et al.

What foods prevent chromosomal abnormalities? ›

Preventing Birth Defects
  • Take a vitamin with 400 micrograms of folic acid every day. ...
  • Foods with folic acid include : okra, pinto beans, navy beans, mustard green s, kale, spinach, chicken liver, beef liver, orange juice, asparagus, broccoli, avocado, green peas, cauliflower, tomato juice, peanuts, and cantaloupe.

Which mother is at greatest risk of having a child with a chromosomal abnormality? ›

A woman age 35 years or older is at higher risk of having a baby with a chromosomal abnormality. This is because errors in meiosis may be more likely to happen as a result of the aging process. Women are born with all of their eggs already in their ovaries. The eggs begin to mature during puberty.

What causes chromosomal abnormalities in early pregnancy? ›

Chromosomal abnormalities occur because of cell division that does not go as planned. Typical cell division happens by either mitosis or meiosis. When a cell, comprising 46 chromosomes, splits into two cells, this is called mitosis. The new cells should also have 46 chromosomes each.

Are all my eggs chromosomally abnormal? ›

DNA or chromosome errors are found in 50-70% of older human eggs, along with 20% of eggs of women in their early 20s, says Dr Zielinska. A growing number of trisomic foetuses, which have 47 chromosomes instead of 46, have been reported in the past decade.

What is a chromosome doctor called? ›

A medical geneticist is a doctor who specializes in diagnosing and treating genetic disorders or conditions. Medical geneticists also counsel individuals and families at risk for certain genetic disorders or cancers.

What are the 3 most common chromosomal abnormalities? ›

Some of the most common chromosomal abnormalities include: Down's syndrome or trisomy 21. Edward's syndrome or trisomy 18. Patau syndrome or trisomy 13.

What are the 4 main causes of birth defects? ›

Smoking, drinking alcohol, or taking certain drugs during pregnancy. Having certain medical conditions, such as being obese or having uncontrolled diabetes before and during pregnancy. Taking certain medications, such as isotretinoin (a drug used to treat severe acne). Having someone in your family with a birth defect.

Do chromosomal abnormalities run in families? ›

Parents can pass chromosome changes to their children, or they can happen on their own as cells develop. What is genetic counseling? Genetic counseling helps you understand how genes, birth defects and other medical conditions run in families, and how they can affect your health and your baby's health.

What vitamin prevents birth defects? ›

Folic acid is very important because it can help prevent some major birth defects of the baby's brain (anencephaly) and spine (spina bifida). The neural tube forms the early brain and spine.

What is the most common chromosomal cause of miscarriage? ›

Single autosomal trisomies represent the largest class of chromosome abnormalities in spontaneous miscarriages. Trisomy 16 is the most frequent one (18.7% of the single autosomal trisomies), followed by trisomy 22 (18.5%), trisomy 15 (14.2%), and trisomy 21 (12.2%).

What are the chances of having a baby with chromosomal abnormalities? ›

While most babies are born healthy, approximately 3-5% will be affected with certain birth defects or genetic conditions. In all pregnancies, tests are offered that can tell if the pregnancy may be at high risk for a condition called a chromosome abnormality. Decisions about testing in pregnancy are personal.

What percentage of miscarriages are due to chromosomal abnormalities? ›

Approximately 10-15% of recognized pregnancies end in miscarriage. The main cause of miscarriage is attributed to chromosomal abnormalities in the embryos. Approximately 70-80% of miscarriages occur due to chromosomal defects in the embryo.

Who is most likely to have a chromosomal abnormality? ›

Maternal Age: Women are born with all the eggs they will ever have. Some researchers believe that errors can crop up in the eggs' genetic material as they age. Older women are at higher risk of giving birth to babies with chromosome abnormalities than younger women.

Can folic acid prevent chromosomal abnormalities? ›

Folic Acid Can Help Prevent Birth Defects

Folic acid can reduce certain birth defects of the brain and spinal cord by more than 70 percent. These birth defects are called neural tube defects (NTDs). NTDs happen when the spinal cord fails to close properly. The most common neural tube defect is spina bifida.

What age are eggs chromosomally normal? ›

Up to 35 years old, about 70% of your eggs are chromosomally normal, which then decreases to about 50%, and by the time you reach 40 you can expect about 10-15 % of your eggs to be chromosomally normal. Once an egg becomes abnormal, this can't be reversed and egg quality can't be improved.

Are all miscarriages due to chromosomal abnormalities? ›

About 80% of all pregnancy losses occur within the first trimester and are often caused by having missing or extra chromosomes, called aneuploidy. Sporadic errors during chromosomal division and duplication cause aneuploidy.

What is the most common chromosomal abnormality at birth? ›

Down syndrome remains the most common chromosomal condition diagnosed in the United States. Each year, about 6,000 babies born in the United States have Down syndrome. This means that Down syndrome occurs in about 1 in every 700 babies.

How do you know if you have chromosomal abnormalities in pregnancy? ›

The maternal blood screen is a simple blood test. It measures the levels of two proteins, human chorionic gonadotropin (hCG) and pregnancy associated plasma protein A (PAPP-A). If the protein levels are abnormally high or low, there could be a chromosomal disorder in the baby.

Why do I keep miscarrying? ›

What causes recurrent pregnancy loss? Most pregnancy losses result from chromosomal, or genetic, abnormalities, and are random events. The abnormality may come from the egg, the sperm, or the early embryo. Approximately 12-15% of all clinically recognized pregnancies end in miscarriage.

Can IVF prevent chromosomal abnormalities? ›

Genetic abnormalities are extra or missing chromosomes or parts of chromosomes, which is very common in human embryos and here's what can happen. 1. Sometimes, during culture of embryos after IVF, genetically abnormal embryos will not develop.

Who is at risk for having a baby with chromosomal abnormalities? ›

Risks for chromosome abnormalities by maternal age

The risk of chromosomal abnormality increases with maternal age. The chance of having a child affected by Down syndrome increases from about 1 in 1,250 for a woman who conceives at age 25, to about 1 in 100 for a woman who conceives at age 40.

Can sperm cause chromosomal abnormalities? ›

Thus there is consistent evidence for a relationship between these specific morphological sperm abnormalities and abnormal chromosomal constitutions.

What is the most common chromosomal abnormality conceived? ›

Down syndrome, on the other hand, is by far the most common chromosomal abnormality, affecting 1 in 800 babies. The risk of having a child with this condition increases with maternal age, rising exponentially after a woman reaches age 35.


1. Embryonic Chromosomal Abnormality & Miscarriage - Antai Hospitals
(RSA Institute - English Channel)
2. Chromosomal Abnormalities: Trisomy 21,18 & 13 – Embryology | Lecturio
(Lecturio Medical | Free Self-Assessments)
3. What Students Need to Know about Chromosomal Abnormalities.
(British BioMedicine Institute)
4. Chromosomal disorders
(Shomu's Biology)
5. Understanding the Chromosomal Abnormality known as Uniparental Disomy (shortened)
(National Cancer Institute)
6. Chromosomal Abnormalities, Aneuploidy and Non-Disjunction


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