What is a Robertsonian translocation?

Inside of each of your cells are thread-like structures made up of parts called chromosomes. These tightly wound threads are what people mean when they refer to your DNA. It’s a blueprint for cell growth that makes every cell in your body unique to you.

Imagine a jigsaw puzzle that snaps together to create a spiral staircase. That’s how your DNA is structured. Each piece of your DNA strand belongs in a specific place, ensuring that your cells can split apart and multiply with your DNA imprinted inside each one.

A “chromosomal translocation” is the term used to describe when two parts of the puzzle thread join in a way that doesn’t fit. A Robertsonian translocation is the most common kind of human chromosome translocation. About 1 in 1,000 babies born will have this translocation in their DNA. It doesn’t necessarily cause any problems.

A Robertsonian translocation effects acrocentric chromosomes. In an acrocentric chromosome, the narrow region where both halves of the chromosome join is near the very end of the chromosome. In a Robertsonian translocation, acrocentric chromosomes fuse together. This fusing joins two “long arms” of DNA into one.

To make studying genes and their mutations easier, scientists have assigned a number to each chromosome in the human DNA chain. The acrocentric chromosomes in this DNA chain are chromosomes 13, 14, 15, 21, and 22. Common translocation formations include:

  • chromosome 13 with chromosome 14 (the most common Robertsonian translocation and the most common chromosome rearrangement found in humans)
  • chromosome 13 with chromosome 21
  • chromosome 14 with chromosome 21
  • chromosome 15 with chromosome 21
  • chromosome 21 with chromosome 22

Robertsonian translocations involve the long arms of DNA chains fusing together. As cells multiply, this DNA error is copied over and over, and usually the short arms of the DNA chain are lost. The lost information can result in your DNA appearing one full chromosome short of the normal count of 46.

Since DNA chromosomes are linked together into 23 pairs, having an odd number of chromosomes can sometimes indicate that essential genetic information is missing from your DNA. A Robertsonian translocation can also result in an extra copy of one chromosome being included in your DNA. A DNA chain with missing or extra genetic information is referred to as imbalanced.

In most cases, there are no symptoms or visible signs of a Robertsonian translocation. Depending on where in your DNA the translocation occurs, it’s very likely that you won’t experience any side effects of your DNA chain being atypical.

Since chromosomes come in pairs, you can have a Robertsonian translocation that disrupts your DNA strand, but leaves you with all of the genetic information that you need for your cells to multiply correctly. That’s why many people with this condition go through life without ever knowing that they have it.

But even if a Robertsonian translocation doesn’t present a problem within your DNA, you may become a “carrier” of the translocation. This means there’s a possibility of passing missing or extra DNA on to your children. That’s where things get more complicated.

Multiple miscarriages, difficulty getting pregnant, and pregnancies in which the fetus develops a trisomy or other genetic abnormality could be a sign that you or your partner has this translocation.

If you or your partner carry a Robertsonian translocation, you may be at a higher risk for infertility or miscarriage. And when people with this translocation carry a child to term, the child may be at a higher risk for chromosomal imbalance.

If you’ve had more than one miscarriage or know you’ve been pregnant with a fetus that carries a chromosomal imbalance, your doctor may advise genetic testing for a Robertsonian translocation. If either you or your partner has this translocation, a risk assessment that analyzes the DNA you carry as well as genetic counseling may need to be considered for future pregnancies.

A monosomy is a genetic alteration in which one half of a chromosome pair is missing. Robertsonian translocations can result in pregnancies that carry monosomy 14 and monosomy 21. Both are considered nonviable.

A trisomy is a genetic alteration in which there is an extra copy of a chromosome in a DNA strand, throwing the chain off balance. A Robertsonian translocation can result in trisomy 14 or trisomy 21. Trisomy 21 is also known as Down syndrome.

Down syndrome is the world’s most common genetic disorder. If your Robertsonian translocation fuses another chromosome with chromosome 21, you may be genetically more predisposed to have a baby with Down syndrome.

Patau syndrome is a rare genetic condition that can cause heart defects and brain and spinal cord abnormalities. Patau syndrome is a result of an extra copy of chromosome 13 in a developing fetus’s DNA.

If your Robertsonian translocation fuses chromosome 13 with another chromosome, you may be a carrier for Patau syndrome. Most cases of this trisomy aren’t inherited, but it’s possible. In about 20 percent of cases of Patau syndrome, a translocation plays a part in the syndrome’s appearance.

Babies born with Patau syndrome rarely live more than one year. Other monosomies and trisomies that can occur with Robertsonian translocations are nonviable. This is why having a Robertsonian translocation goes along with a higher risk of miscarriage.

Typically, people born with a Robertsonian translocation are healthy and have average life expectancies. But finding out you have this genetic abnormality, and the possibility of it affecting your pregnancy or your children, can be confusing and stressful.

Viability outcomes for certain genetic conditions vary considerably. Factors such as maternal age and health history play into statistics about translocation carriers and their pregnancies.

Some chromosome imbalances, such as monosomies 14 and 21 and trisomy 14, don’t carry a good outlook. Trisomy 13 and trisomy 21 both result in genetic conditions that are viable, but can have serious effects. Then there are translocation outcomes that don’t carry any genetic consequence at all.

Speak with your doctor if you suspect or know that you have a Robertsonian translocation. Genetic counseling, breakthroughs in research, and clinical trials can all increase your odds of having successful pregnancies.